Author Topic: Pinging from cylinder #5  (Read 27805 times)

Ulfi

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Pinging from cylinder #5
« on: May 05, 2008, 04:59:26 »
We still haven't sorted the uneven running between 0 and 2000 rpm (see "jerky driving"), but another problem has surfaced. The engine has a constant metallic pinging sound from cylinder 5 (sound like my Land Rover diesel when idling), the valve clearance and return spring has been checked and found not guilty. I hadn't paid much attention to it before my mechanic pointed it out, now it really annoys me. The previous owner says that the sound has been there for years.
A recent compression test didn't come up with any clues either.
What could this be?

Thanks in advance

Ulf

ja17

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Re: Pinging from cylinder #5
« Reply #1 on: May 05, 2008, 22:29:55 »
Hello Ulf,

Check to make sure the valve cover hold down straps are not touching the camshaft (they pull inward when the valve cover is tightened). If so you can get this kind of noise. Also if the valve cover bolts are too long, they can contact the camshaft making a tapping noise.

If these items are ok, remove each rocker arm and examine them for flat spots on their rubbing surface, or unusual rub marks on the bottom (where they pass over the upper spring retainer).

Joe Alexander
Blacklick, Ohio
Joe Alexander
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Ulfi

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Re: Pinging from cylinder #5
« Reply #2 on: May 06, 2008, 03:20:07 »
Thanks Joe! I'll have my mechanic check those things before they pull everything else apart - today it's been exactly two agonizing months since I delivered the car to my mechanic...and the weather forecast promises sun and 23 C the rest of the week...dang!

Ulf

Longtooth

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Re: Pinging from cylinder #5
« Reply #3 on: May 06, 2008, 05:16:51 »
If the sound is only on cylinder #5, and is due to a detonation problem, remove the spark-plug wire from #5 plug and see if the pinging sound goes away. If it does, then it's a detonation problem within the combustion chamber on #5... if so, check fuel line to #5 (insufficient fuel, too lean, or injector nozzel screwed up so fuel / air density is not uniform in #5, hence improperly igniting fuel in that chamber).  Also, check cam lobe on #5 intake. .. but if valve tappet clearances were properly set, then I wouldn't expect the cam lobe wear on #5 to cause the problem on a consistant long term basis ("The previous owner says that the sound has been there for years.")


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Ulfi

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Re: Pinging from cylinder #5
« Reply #4 on: May 07, 2008, 01:44:54 »
Thanks Longtooth - I was just about to elaborate on that as the sound stops the moment you remove the spark plug wire. Before taking any drastic measures like removing the engine (which is necessary to gain access to that cylinder) I'll try to replace the injector nozzle to see if it cures the problem.
So I believe you are correct in assuming that it is a detonation problem, let's see if the nozzle thing works...

Best regards

Ulf

Ulfi

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Re: Pinging from cylinder #5
« Reply #5 on: June 02, 2008, 03:06:52 »
Have now replaced the injector nozzle which didn't really improve matters at all - so it looks as if the only solution is to pull the engine out for a thourough examination. My question is: would you consider driving the car and ignoring the annoying sound for the summer and wait until September to fix it or am I staring at a potential disaster in doing so? I'm not really looking forward to the expense and having no Pagoda during the summer...but I wouldn't want to go through an expensive complete rebuild of the engine just because Iof my stupid impatience either...

Thanks in advance

Ulf

glennard

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Re: Pinging from cylinder #5
« Reply #6 on: June 02, 2008, 04:46:29 »
Does it change/go away/etc when you advance/retard the timing?  Could be connecting rod bearings?  Try 50 wt oil?(Castrol for 75K+ engines)
« Last Edit: June 02, 2008, 05:15:21 by glennard »

waqas

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Re: Pinging from cylinder #5
« Reply #7 on: June 02, 2008, 23:34:15 »
You might want to also remove the distributor cap and inspect the rotor and contact to cylinder 5.
Waqas (Wa-kaas) in Austin, Texas

Ulfi

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Re: Pinging from cylinder #5
« Reply #8 on: June 04, 2008, 05:21:34 »
The car will be with my mechanic on Monday, I'll have him check the timing (which I assume is ok, though...), take a look inside the distributor (which unfortunately I assume he has done already - see "jerky driving"). This could be related to the issue with the injection pump as the car has a considerable CO2-output when idling, perhaps this cylinder is getting too rich a mixture which has caused wear...
I'll keep you guys posted on this - thanks for your helpful advices so far!

Ulf

glennard

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Re: Pinging from cylinder #5
« Reply #9 on: June 04, 2008, 07:57:06 »
Have you disconnected the fuel line to #5 to see what happens with no gas to #5?

Longtooth

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Re: Pinging from cylinder #5
« Reply #10 on: June 05, 2008, 02:21:20 »
Ulfi, since sound goes away when not detonating on cyl #5 (applying no spark to #5), and injector nozzel was replaced with no change in sound, it's a detonation problem if it's a "pinging"... high pitched sound... or a worn bearing sleeve on rod at either piston pin or crank shaft end if it's a more thunk-thunk sound --- lower pitch sound.  Since you call it a "metallic pinging" sound it points to detonation occurring too soon on Cylinder #5.  

There are 2 reasons I'm aware of why detonation can occur too soon or unevenly on a given cylinder and not on the others.

1) combustion chamber or valves caked with carbon on that cylinder, hence excess and hot-spots of heat remains in the combustion chamber and forces uneven combustion advance during detonation.. hence pinging sound; Remove cylinder head and check valve faces, edges, and seats, top of piston for excessive carbon build-up and/or poor seating of intake valve.

2) Intake valve opening too soon or too late.. I think the former more than the latter, but I'm guessing about which is more likely the problem. Remove valve cover & check valve tappet clearance (gap) and for wear patterns on Cylinder #5 intake valve lobe. I know you (or your mechanic) found valve tappet clearance found 'not guilty', so this may be in fact not the cause... but it's the cheapest way to rule it out for absolute sure by double checking it against all the other tappet clearances before being forced to remove the head.... a far more expensive process.  

As to whether or not to keep driving it while sound persists, it's my humble opinion that an ounce of prevention is worth a pound of cure... meaning only that a detonation problem is putting excessive forces on the piston pin, rod, rod bearings, and top surface of piston.  Sooner or later one of those things are going to give and you're expense will triple in fixing the resulting damages.

I don't know if the crankshaft / rod bearing lobe can be accessed by removing the oil pan on this engine but if so it's another way to check the whether the bearing sleeves (rod to crankshaft) are excessively worn already on Cylinder #5 (without removing the engine).  I would doubt this as a primary source since my expectation would be that it would produce a more thunking (lower pitch) sound than a "pinging" sound, but if it's possible to check the lower bearing sleeves on the rod by removing the oil pan then it's a lot cheaper than removing the engine I think.  The sound is being generated somewhere between the combustion chamber and the crankshaft... I'd bet on the combustion chamber issues, but with length of time the sound has been prevelant (referring to prior owner's statement) it may be that some things have also worn more than normal even though not generating the sound directly itself.

It depends perhaps on whether your mechanic is more interested in racking up hours of labor than identifying your problem source with the fewest investigative hours possible.  Sorry to be distrusting of mechanics, but I've know more than a few who specialize in customer's ignorance of things to rack up the hours to go to great lengths and expense when a far lower labor hour method will suffice with equal ability to identify (and even enable fixing) the problem.


Ulfi

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Re: Pinging from cylinder #5
« Reply #11 on: June 06, 2008, 01:35:45 »
quote:
Originally posted by glennard

Have you disconnected the fuel line to #5 to see what happens with no gas to #5?



Will try it tomorrow (have sent wife and kids away so I'm free to fiddle), but I assume that it will do the same as disconnecting the spark plug cable - that the sound will disappear...but let's see...

Ulf

Ulfi

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Re: Pinging from cylinder #5
« Reply #12 on: June 06, 2008, 01:39:26 »
The nozzle that I replaced was covered in gunk and oily deposits, so you might be on to something - have printed your reply for my mechanic to use (he seems like a pretty fair guy, by the way - Denmark is a small country where it is easy to ruin your own reputation/business if a unfavorable rumour gets started).

A very nice weekend to you!

Ulf

Longtooth

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Re: Pinging from cylinder #5
« Reply #13 on: June 06, 2008, 03:21:12 »
Ulfi, sorry 'bout my mechanic statement... I was referring to my experience in US.

The oily gunk and deposits on the fuel nozzel you replaced adds to the probability that the combustion chamber in Cyl #5 is fouled with excess carbon deposits which changes the combustion process within the chamber, leading to one very well known source of "pinging"... uneven explosion during combustion.  It doesn't prove it, but is additional evidence of a detonation source problem along with the fact that removing the spark eliminates the sound.

Given that the prior owner told you the pinging sound was "always" there, the question then becomes what condition exists or existed to create the excess carbon deposits in the 1st place.  A fouled plug or poor spark at the spark-plug gap would aid this process over time..... and once the carbon deposits were established, the likelyhood of an improved spark or plug condition wouldn't materially undo the deposits.  A quick check of the spark plug deposits would tell you whether the currently used plugs are also getting fouled prematurely or at all in Cyl. #5.  If so then it's may be due to a poor seal on the oil ring (either worn, cracked, or sealed to the piston ring gap).

If, on the other hand, the spark plug points are not being fouled on your current plugs and driving, then there would be no reason to suspect a worn or broken oil ring having caused the initial combustion chamber assumed excess carbon deposits, so it could be simply that at one time the prior owner had a poor plug or contact to it for some period of time while the carbon built up in the chamber... and since then he "always heard the sound".  

If the distributor cap hasn't been replaced, you can check the contact for roter to Cyl. #5 contact on the distributor cap for signs of arcing.... an indication of an inefficient transfer of electrical conduction from rotor to the Cyl #5 distributor contact.... anothe poster suggested this previously.... waqas.

The point is that something's causing the Cyl #5 chamber to foul or having at one time been caused to foul and assumedly then having create excess carbon build-up within the chamber... on piston surface, valve edges, etc.  ... leading to the uneven detonation in that cylinder without being created in the others.

By the way, the higher than normal CO2 emissions would be expected from a poor detonation condition in one cylinder (which is producing ~17% of the total emission if all cylinder's combustion were evenly distributed and equal... so if Cyl. #5 is less efficient in combustion process, then it's going to produce greater levels of C02 than the others, leading to higher than normal C02 emissions ... certainly not the only reason for higher CO2 emissions by a long shot, but still in the direction of expectations with poor / uneven detonation process in Cyl #5.

In other words, all the symptoms described thus far are consistant with a detonation problem, uneven detonation more specifically, in Cyl. #5.   If the combustion chamber is found indeed to have excess carbon build-up on valves &/or piston head, then the issue that will have to be dealt with ultimately is the source and cause.

Ultimately the source will be due to either just poor spark (see distributor cap issue above) which caused the excessive carbon build up in the 1st place... having a good spark won't fix it, so the excess carbon has to be removed in any event, or given the fouling condition noted on the fuel nozzel, a possible oil ring seating, wear, or crack in that ring of that cylinder.  If the latter is found ultimately to be the source, then all other cylinder's are equally suspect in having similar wear, or aging to lead to cracking or sticking to the piston ring gap it's supposed to slide & rotate in (though not sufficient to have created enough fouling and carbon build-up to cause "pinging" yet).

By the way, another source for excess oil in the combustion process are the valve guides... excess wear.... which would definitely lead to excess carbon build-up on the valve edges.  If that's the case then the head needs to be reconditioned... new valve guides, valves, and valve seats ground.

Coincidentally, perhaps, when I bought my 250SL in '84, Cyl #5's spark plug was fouling so much that I had to clean it or replace the plug every thousand miles or so... after driving the car for about 5-6k miles it got so bad that I had to clean the plug every 500 miles or so... a process I quit doing by not driving the car for the next 15 years or so... just parked it one day after work in it's spot in the garage and forgot to drive it again for 15 years.  When I finally had the engine rebuilt, the oil ring in cylinder #5 was cracked... the mechanics (a pure MB shop specializing in the SL's and other 60's era MB's) told me that Cylinder #5 for some reason is the one most prone to problems with ring wear... they thought it was due to Cyl #5 heat dissipation or Cylinder warpage being geater than in the others.  I don't know if their statement has merit in fact or whether they were just trying to get me off their back with any old explanation that sounded good... but ...this is on the 7 main bearing 2.5 liter engine.  It's certainly possible for the engine heat dissipation to be uneven from one cylinder to another and for one in particular to have issues, but I can't say this is a fact for the 2.5 or 2.8 liter 7 main bearing engine or not.  Food for thought though.
« Last Edit: June 06, 2008, 03:37:44 by Longtooth »

graphic66

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Re: Pinging from cylinder #5
« Reply #14 on: June 06, 2008, 06:22:25 »
You might try decarbonizing your engine using the aerosol decarbonizer available for marine applications. Yamaha makes one, OMC makes one called engine tuner, there are also generic versions. The stuff is great at dissolving carbon buildup. You spray it in the intake while running and shut the hot engine down and pull the spark plugs and squirt it in the cylinders. Let it set overnight. Start it up the next day and run the engine until hot. You should then change the oil. OMC also makes a fuel additive to help stop the carbon buildup. I use the aerosol in all my engines at every oil change. It is also a great carb cleaner and parts cleaner. It melts carbon and varnish buildup right off. It might be worth a try.

glennard

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Re: Pinging from cylinder #5
« Reply #15 on: June 06, 2008, 11:03:07 »
How about pulling number 5 plug wire?  What happens?  Still pings?




quote:
Originally posted by glennard

Have you disconnected the fuel line to #5 to see what happens with no gas to #5?


Cees Klumper

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Re: Pinging from cylinder #5
« Reply #16 on: June 06, 2008, 16:15:48 »
quote:
Originally posted by cees klumper

"Thanks Longtooth - I was just about to elaborate on that as the sound stops the moment you remove the spark plug wire."

quote:
Originally posted by glennard

How about pulling number 5 plug wire?  What happens?  Still pings?



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Ulfi

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Re: Pinging from cylinder #5
« Reply #17 on: June 10, 2008, 04:14:47 »
Longtooth: Do you think the condition of that cylinder could be caused by the problems with the injection pump as described in "Jerky Driving"? That issue is still not sorted completely, but we managed to find a setting that will do for the summer and then replace the pump with a reconditioned unit after the summer.
I replaced the spark plugs with Bosch-units supplied as parts of a service kit from SLS, the old ones were not that fouled and all looked the same...
Crossing my fingers that it is not an oil ring as this means taking the entire engine out...
Graphic66: I'll give that aerosol a go in the weekend

Best regards

Ulf

Longtooth

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Re: Pinging from cylinder #5
« Reply #18 on: June 14, 2008, 02:58:19 »
Ulfi, if spark plugs from all cylinders looked same as on #5, and none were especially fouled, then the oil ring isn't an issue as cause of a possible carbon build-up within combustioin chamber/piston head and thus detonation (pinging) problem on Cyl #5.

This doesn't preclude a carbon build-up hasn't occurred within Cyl #5 due to some prior condition with previous owner however.  So that's still the primary source of the problem based on your other statements.  In particular, you said

"The nozzle that I replaced was covered in gunk and oily deposits... "

and that it's replacement didn't change the pinging sound.  I haven't pulled any of my injection nozzels so can't offer any relative assessment of whether or to what degree the nozzels are covered in gunk and oily deposits however even on normal running engines --- you might want to check other cylinder's injection nozzels (at least 2 of the other 5) to see if they're not nearly as 'dirty' as the one you replaced in Cyl #5.  Graphic66's suggestion is a good (and cheap/easy) way to determine if carbon build-up reduction in Cyl #5 changes the pinging sound or condition.  

It is possible that your "jerky driving" symptom and the pinging sound in Cyl #5 are related, though I'm not sure this wouldn't relate more to a general problem on fuel or spark delivery than a problem with just one cylinder.  A single cylinder problem in detonation or lack of spark will give a rough idle, and at speed, a lower power with rough running, but still running, engine... not "jerky" engine.  The only way it might appear to be "jerky" if only one cylinder was being affected is if that one cylinder were intermittantly firing or intermittantly getting fuel or spark.  If intermittantly getting a spark, then it would also tend to build up more gunk and carbon deposits in that cylinder... a possible means for the prior owner having created the condition if it exists in fact.  An intermittant fuel delivery problem (lack of it) on one cylinder wouldn't provide any increase in carbon build-up or gunk which would lead to the detonation pinging problem you're experiencing on that cylinder though.  

Remember that the problem is a detonation (combustion process) problem... carbon build up within the chamber modifies the advance of the combustion process, causing the pinging sound.  If carbon build up has occurred on the intake valve seat or seating surfaces then some fuel is getting into the chamber sooner than the valve timing requires, and this also modifies how the combustion process proceeds. Similarly if the exhaust valve seats or surfaces are not letting the exhaust valve close completly... as fuel/air is being injected there's an escape path out the not fully closed exhaust value.  However, in either caes I'd expect to see some reduction in compression on that cylinder... so if as you've stated there's no compression differences of Cyl #5 from the others, then I'd rule out any seating problems with either valve.

The key symptom is still that when you disconnect the ignition line to spark plug #5 the pinging sound disappears... no spark, no combustion, no pinging... hence detonation problem. Classically this is due to too much advance on the ignition timing or to a combustion problem within a given cylinder which is due to something within the chamber that changes the design of the combustion process... carbon build-up being the one most common (others would relate to something that changed the shape of the combustion chamber.. notably a damaged piston head... which might also include a bent rod or damaged piston pin).

Just for diagnostic purposes, what happens if you retard the spark more than spec's?  Does the pinging sound in Cyl #5 dissappear before the engine starts to stall entirely?  If you reverse it and advance the spark more than spec's does the pinging sound change at some level of advance -- become more or less?  .. or do other cylinder's join in starting to ping also?

If cyl #5 remains the dominant one in pinging under either of the above circumstances , I'd begin to suspect a cam lobe wear problem on the intake lobe for Cyl #5.  If the lobe is worn on that cylinder, then the intake valve opens too late or begins opening later than spec'ed and / or by lesser magnitude, and closes earlier than spec'ed.  While I fully admit that I don't understand how that would change the combustion process, it certainly would at some level... perhaps just enough so that when properly timed, that one cylinder is affected enough to cause pinging.  

The only reason I'd not expect this as a source is that I assume all cam lobe wear would be approximately equal across all cylinders, but if, at some time in the past something was mal-adjusted for a period and caused cyl. #5 lobe to wear more than the others, then this could have occurred.  Since the tappets are being set to a given clearance at a given timing (position of rotation) on each valve, a wear problem on one lobe (wear more than others) wouldn't be detected... remember it's the shape of the lobe that opens and closes a valve... the maximum opening magnitude is determined only by the location of the high-point of the lobe... but it's high point has to be coincident with the time it's supposed to be at maximum opening.  A valve adjustment process and spec's assume the cam lobes are within spec's in shape.

Anyway, I don't know how to check a cam lobe for whether it's worn out of spec's in shape or not, but I do know that an excessively worn (damaged thru wear) lobe can be seen.  I also assume however, that the mechanic involved would have looked at the cam lobes as he /she were adjusting the valves, checking for valve spring breaks, etc... and should have seen evidence of excessive wear on the intake (or possibly exhaust) valve lobe for Cyl. #5 if that were the case.

This is a perhaps silly suggestion, but is mechanic sure that the injection nozzel is inserted correctly... i.e. that there were no symptoms on the threads of the replaced nozzel that indicated it might have been cross threaded or not fully seated?  If there were some cross threading in the intake (female side) then the new nozzel would also have been affected when inserted.  Just a thought to wring out any of the most obvious things.

Shvegel

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Re: Pinging from cylinder #5
« Reply #19 on: June 19, 2008, 01:20:14 »
A couple of points if they have not been made.

A compression test should reveal high compression on number 5 if it was pinging due to excess carbon.

The injector nozzle is in the intake runner and not the combustion chamber. Gunk on the nozzle does not mean gunk in the combustion chamber.

If the noise is going away when you pull the wire I am afraid what you might be hearing MIGHT be one of two things.

1 A loose connecting rod big or small end.

2 piston slap which is the piston rocking over on ignition causing the piston crown to strike the side of the cylinder. Piston slap is usually caused by high mileage cylinder/piston wear or overheating Which would be very unusual in only one cylinder.

Regardless your mechanic could look in the cylinder with a borescope and see if there is a carbon buildup or perhaps valve/piston contact. Or you might try turning the engine over by hand until piston 5 is on the down stroke and reaching in the spark plug hole with a wooden dowel and pushing down on the piston top and see if the piston moves down which would indicate a loose rod or what is termed a "Rod Knock". This isn't a definitive test but if it is loose enough you might find it.

The reason a rod knock will go away when you remove the ignition lead from the sparkplug is that it no longer has the force of the explosion in the combustion chamber the drive the piston into the rod when the spark plug fires.





« Last Edit: June 20, 2008, 10:40:08 by Shvegel »

Ulfi

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Re: Pinging from cylinder #5
« Reply #20 on: June 23, 2008, 02:16:53 »
Thanks Shvegel - very helpful and also a good excuse to call my mechanic...

Ulf

Ulfi

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Re: Pinging from cylinder #5
« Reply #21 on: June 23, 2008, 02:19:27 »
My mechanic claims that if the pinging is caused by a loose connecting rod end or piston slap, the only solution is a complete overhaul (at a huge cost) and not merely fixing that cylinder - what is your opinion on that?

Ulf

Shvegel

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Re: Pinging from cylinder #5
« Reply #22 on: June 25, 2008, 20:14:24 »
Sorry to say he's right. By the time you replaced/repaired a connecting rod or one bad piston you would have done:

Removed engine from vehicle.

Removed cylinder head.

Removed oil pan.

If it is a bad piston you would have to take the engine the rest of the way apart to machine the cylinder to accept a new piston or find a used stock bore piston to put in.

If it is a connecting rod problem you might have to send the crankshaft out to be machined and the engine again would be completly apart.

So your at the point where you are $2,500 US dollars(or 6 Euros...only kidding) into the project plus parts or close to 40 percent of the cost of the rebuilt engine You will have 5 more pistons that have gone up and down as many times as the one that failed and your valves will probably be worn as well.

At this point I would consider a second opinion or even a first if your mechanic in unwilling or unable to offer a concrete diagnosis. I am not saying that I or anyone else could say what is causing it beyond a shadow of a doubt but sometime equipment or experience with a particular engine can help.

All that said later Volvo 240's are known for piston slap and it doesn't effect the engine at all. If it is a rod knock however you are taking a risk that it might fail suddenly and ruin the engine completly. I don't know the market price for a used SL engine but I bet it's not cheap.

 



« Last Edit: June 25, 2008, 20:30:18 by Shvegel »

waqas

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Re: Pinging from cylinder #5
« Reply #23 on: June 26, 2008, 00:03:09 »
I think you should eliminate all other possibilities before doing anything drastic (like engine rebuild).  Patrick has listed a couple of things to try out... might be a good idea to first have your mechanic do these first before anything major...


quote:
Originally posted by Shvegel

Regardless your mechanic could look in the cylinder with a borescope and see if there is a carbon buildup or perhaps valve/piston contact. Or you might try turning the engine over by hand until piston 5 is on the down stroke and reaching in the spark plug hole with a wooden dowel and pushing down on the piston top and see if the piston moves down which would indicate a loose rod or what is termed a "Rod Knock". This isn't a definitive test but if it is loose enough you might find it.

Waqas (Wa-kaas) in Austin, Texas

Ulfi

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Re: Pinging from cylinder #5
« Reply #24 on: June 27, 2008, 02:13:46 »
We're talking 10.000 USD for a rebuild - and that's not including removal and refitting of the engine + I still have the injection pump issue to deal with...
I'll give him until late next week and then get a second opinion, as I simply can't afford the rebuild at the moment.
I'll keep my fingers crossed that it's an easy fix, but looks like we are running out of cheap options here...

Ulf