280SL 3.5L Engine swap requirements and contact

[justininia]

Good day to everyone.

We are in the middle of rebuilding a 1971 280SL with a 3.5L V8.  The chassis is painted and the engine is sitting waiting to get hoisted into the car.  Alas, we are already noticing some problem areas.  The passenger side exhaust manifold does not clear the steering arm or the firewall.  The power brake unit looks as though it needs to be moved 1.5" to the outside to fit correctly. 

We've heard of people making the switch which is why we are doing it.  I've been looking through the posts and seeing a lot of people reference the 3.5 engine swap but not finding anyone who has made the switch. (This is most likely due to my search criteria.) 

What I am hoping for is to find someone who has performed the engine installation and is willing to share the experience, good and bad, and be a point of contact for questions should they arise.  There looks to be several key areas that need addressing and a person with the actual experience would be extremely beneficial.  Is there someone with the experience who wouldn't mind being some electronic help?

Thanks for reading my post and happy motoring everyone.
Justin

[JamesL]

In essence I am about as much use as a chocolate fireguard in this thread but the one contribution I can make is:

Which 3.5?
http://www.sl113.org/forums/index.php?topic=15199.0

http://www.sl113.org/forums/index.php?topic=6046.0

http://www.sl113.org/forums/index.php?topic=2023.0

[GGR]

I didn't do a 3.5 swap in a Pagoda but I am in the process of fitting a 5.6. They are basically the same engines, the M117 having a bit higher block deck.

I know the 3.5 is period correct but if I were you I would seriously reconsider it: It is an iron block and is very heavy (I owned several W108/111 coupes fitted with one so I know it quite well). The Pagoda has this diving problem under hard braking and adding weight in the front is not going to help. Hatch & Sons claims the 3.5 is only 29lb heavier than the original M130 but I'm quite positive it's much heavier than that. The overall balance of the car will  also be affected and it will be nose heavy.

If I were you I would consider a later M116 (3.8 or 4.2) or M117 (5.0 or 5.6). They are basically the same engine but with an aluminum block. They are not heavier than the original M130 and they offer a bigger displacement. They can be dressed in D-jet trim to look period correct using the 3.5 or 4.5 D-jet hardware. I did it on a 5.0 M117 with very good results. otherwise the early K-jet system is very simple and reliable (This is the system I will be using on my 5.6 Pagoda).

To help answering some of your questions:

Some r107 (3.5 or 3.8?) came with  a right exhaust manifold which I believe will clear the steering arm/firewall. It has only one outlet when I guess yours have a double outlet. If you go the M117 route like me then the 560 SL manifold would also clear.

For the brake booster you have two options:

You can drill the firewall more on the left and shift the whole booster/pedal assy to the left. Or you can tillt the aluminum bracket by 45 degrees. this would require adaptor plates at both ends of the bracket to get the pedal assy and booster straight. I didn't decide which route to go for myself yet.

You may also use a smaller diameter booster, as found on some w114s for example.  I did that on my coupe conversion and it helped clearing the left cam cover.

Are you using an auto transmission or a manual transmission? If a manual one with the side shift system you will also have clearance problems in the trans tunnel. 

Keep us posted !

[justininia]

Thanks for the replies.

In looking at that r107 exhaust, it looks like it will work.  Now we just have to find one.  

We have the period correct engine to place in the car, heavy steel and all.  We are using the front cross member out of a 280SE and heavier springs and shocks which should address the weight issues.  It looks like the transmission (automatic) should fit but we have only measured, not actually placed the unit in the car.  

The brake booster is already rebuilt so it looks like we are going to move it over about 3/4" and add a reinforcing plate to the firewall.  That is the easiest part of the modifications as we also have a modified pedal assembly already.

Thanks for the help.  I am sure more questions will pop up as we get closer to fitting a drive shaft and who knows what else.

Justin

[GGR]

Apart from the very early fintails, front axle carrier is common to all these cars (108, 109, 110, 111, 112, 113). You may consider using some W108/111 3.5 front springs, or even some W108 4.5 ones. It will help the diving issue. You can adjust height with the thickness of the top rubber shim, if needed. The 280SE 6 cylinder car springs may be a bit too weak. You may also consider transfering the battery behind the passenger seat (use a dry cell one in the passenger compartment) or in the trunck to help re-balance the weight distribution of the car.

You may use a W108/109/111 3.5 or a W108/109 4.5 pedal assembly as the brake pedal will have the correct offset and will seat where it should after you move the booster over: these cars also had their boosters more to the left to accomodate the V8 and thus the pedal is ending more to the right to compensate.

I would be curious to see how you modified the front right of the engine bay. I have fitted the alternator higher on my 5.6 and I think it will clear the sheet metal around the air filter housing, but I'm nor sure yet. Could you post a picture of that area? I see on the one you posted that you removed that part around the air filter. How are you going to hold the radiator?

Thanks.

[justininia]

Good day!

We have a 116 and 117 set of exhaust manifolds with the only discernable difference being the drop for deck height.  The R107 manifolds look like the right fit for the job.  Would the manifolds from the aluminum 116 or 117 directly bolt up to the cast iron 116 engine?

Still working on modifying the mounting space for the brakes.  We heated the pedal arm and bent it rather than try the SE pedal assembly.  We are also playing the guessing game on how far over to move the booster unit.  My preference is just far enough to slip a socket onto the valve cover.  It makes the brake unit the last to install but that isn't the end of the world.

I'll get some pictures this afternoon.  Right now, all that has been modified in the engine compartment is removin that Sheila.  We are going to see if the radiator can be machined for a larger cooling capacity but hope to use the original radiator and mounts.

Cheers,
Justin

[GGR]

Aluminum block M117s are fitted with heads with different port sizes and are also centered differently (compare exhaust gaskets to see what I mean). Heads fitted on iron block M116 and M117 and aluminum block M116 all have the ports sized and centered in the same way. In short, on an iron block M116 3.5 you can use other M116 (iron and aluminum block) exhaust manifolds and iron block M117 4.5 manifolds. You cannot use aluminum block M117 (5.0 and 5.6) manifolds. The latter will bolt on but the ports won't align properly and you will loose power.

For the booster, you should have at least two fingers clearance to allow for engine and front end mounts play. As mentioned earlier, you can fit a smaller diameter booster to help with the clearance.

Another point: W113 engine arms locate the engine a bit lower compared with sedan engine arms. I presume you are using 3.5/4.5 W108/109 engine arms. As a result your engine may sit a bit higher than it should. You should work on this and make sure the engine is properly located as it will also influence the location of the brake booster.

[RCREEM]

Guten tag!

First off, thank you very much for all the help so far.  It has truly been welcomed.  Justin and I are working together on my car to get it up and going.  He's been kind enough to post the questions for me.

With the 116 arms on, there is only about an inch of clearance from the bottom of the engine to the front cross member.  With lower arms, I would think the deterioration of the motor mounts might cause it to ride on the steel.  We have a set of M130 (PN: 127 xx...) engine arms from a 113 chassis.  Those arms are longer and don't seem to fit plus they have the platform for the oil cooler. 

We decided on 2.125" to the driver's side should offer enough clearance for the brake booster from the engine and provide enough space for the remaining items that get routed through the firewall.  We also discovered that means moving the bracket under the steering column to support the pedal assembly.  Not a tremendous problem just the proverbial "one more thing".  Now off to get a 25/32 drill bit for the pedal arm.

Again, thank you for all the help you've provided thus far.

Dick

[GGR]

First off, thank you very much for all the help so far.  It has truly been welcomed.

You're welcome !

With the 116 arms on, there is only about an inch of clearance from the bottom of the engine to the front cross member.  With lower arms, I would think the deterioration of the motor mounts might cause it to ride on the steel.  We have a set of M130 (PN: 127 xx...) engine arms from a 113 chassis.  Those arms are longer and don't seem to fit plus they have the platform for the oil cooler. 

What chassis are your engine arms coming from? W108/109/111? or 107? or 116? They are not the same. Again, I presume you are using the 108/109/111 V8 ones.

What I was trying to say is that the Pagoda engine sits lower than in the sedans relative to the front axle carrier. I don't know by how much, I would need to compare W113 and sedan L6 engine arms. I believe the difference may be between 1 and 2 cm. You may want to reproduce this difference as much as possible so as not to have too much misalignement/angle with the driveshaft (otherwise you may end up with some vibrations). The W108/109/111 engine arms will put your crankshaft rotation axis at the same lavel as on sedans. If you feel you don't have enough clearance with the front axle carrier you could fit some shims in between the front axle mounts and the chassis rails to have the axle sit a tad lower (let's say by 1 cm; 6.3s have 2cm shims there). Don't lower it too much as you still want all the steering couplings to clear under the engine. If your car sits too high as a result you can fit thinner rubber shims on top of the front springs or shorten the springs ( but I think you will be OK because the 3.5 motor is way heavier than the L6 and you're using L6 springs so they will compress more).

Anyway, it should be a step by step process and you should then adjust accordingly at each step. I hopefully be there soon with my 5.6, though I will start the conversion from the rear first.

Keep us posted ! 

[RCREEM]

Our "donor" car(s) were a '71 300 SEL which gave its core 3.5 M116 engine and a rebuilt auto trans.  We also dismantled a '72 280SE 4.5 junker and are using its complete front suspension assembly, incl springs, slotted rotors with the bigger brake pads, etc.  We have gone clear through it, so its pretty solid, and we hope it will have enough support with the 4.5 springs.  The motor support arms are from the W109 /3.5 engine.  The 113 is a '70 280SL chassis, but had no running gear when we rescued it (as a stripped hulk that had been "ebayed for parts"), so we don't have any way to compare the engine height in the chassis.  We have a couple of L6 engines, but both are out of sedans, incl the "127" part number support arms.  We really appreciate your in-depth explanation about the height in-chassis and will look into shimming the front sub-frame assembly down.  We don't have the (later model) auto trans in yet, but we are concerned about drive line angle.  Your info helps explain why the Hatch cars have custom support arms and transmisson mount!

We rebuilt and mounted the brake pedal box assembly with the offset pedal from the 280SE 4.5 today and moved the booster 1 1/2" left.  That should clear and looks to be about "two fingers"!  Appreciate that advice, too!

Hope you'll also keep us up to date on your 5.6 adventure!

Dick & Justin

[GGR]

I'm not sure the 4.5 front brakes have bigger brake pads, but the rotors are vented which is surely a big plus. You may consider carbon/kevlar pads, they do a good job on my Coupe and people have good experience with them on this board.

I will be using "flatter" engine mounts to position the engine lower by one to two centimeters. I have used generic hot rod engine mounts fitted on the original back plates. I did not fit the engine on the front axle yet, so I don't know if I have enough clearance with the oil pan. If not I will see if I need to lower the front axle carrier. If I were you I would start by fitting the engine on its mounts without lowering the front axle carrier yet, and see if the flex disk works ok or if it is distorted. For that you need to have the car sitting on its wheels and turn the driveshaft. If the flex disc is distorted it will be quite obvious. Don't do this with wheels pending because the engine will sit lower due to front axle carrier mounts play. I'm saying this because I had the opposite problem on my Coupe conversion: I had to have the engine sit a bit higher for the tri-Y downpipes to clear the steering linkages etc. and I ended up with a bit of growling noises in 5th as the flex disk was distorting a bit. Agaist all odds the solution was to lower the trans mount a bit when logic would have dictated the contrary. So it's better to work on shimming at the end, also because you will have the steering system in place so that you can make sure you're not creaing another problem there.

The 4.5 front springs are the stiffer of the series so I think they will be the best suited for your application. You may end up having to shorten them a bit to have the car sit where it should, but you also will see this in the end when the car is completed.

I suppose you will be using the 4.5 3.27 rear axle too which is thee best suited for your application.

One trick: the SL auto shifter has its "P" position at the bottom, while it is up on the sedans. So just rotate the shifting arm on the trans by 180 degrees to have it work with the Pagoda shifter.

English is not my mother tongue so I do not always see immediately all the different meanings of the words I'm using. Sorry for the booster clearance explanation !

[GGR]

Another point you may consider is that clearance between the driver side exhaust manifold and the steering box is very tight. lowering the engine may have the manifold hit the steering box. A combination of grinding on the manifold, the steering box a slightly tilting the engine to the passenger side may help you with clearance. You may also consider shifting the engine arms left with right. They are not the same length so it may shift the engine a bit towards the right. Again, check all the clearances with the weight of the car on the wheels as otherwise the front axle will sit lower than in driving conditions.

[justininia]

Good day and thanks for all the information, GGR.

We set the engine and transmission in the car over the weekend and with a little wiggling, got it bolted to both motor mounts.  Moving over the brake assembly required us to build a new little bracket under the dash to mount the brake pedal assembly.  The brakes are ready to go, steering is reassembled and ready to be put in post wiring and ducting, and then onto engine components.

One thing we are still out looking for is a set of engine shock absorbers.  We have a set off the 4.5 (280SE) but the shock is too large for the distance covered and the bracket that mounts to the engine isn't at a good angle.  I've reached out to a few salvage yards to find a 3.5L set but haven't had any luck yet. 

Another issue is going to be finding a radiator with enough cooling capacity or trying to fit one of the SE radiators in the car.   I understand why you were interested in that right side of the engine bay now.  Fitting in a larger radiator will most likely force it to be mounted lower to allow the hood to properly close. 

Progress... 

Thanks again for all the advice and information.
Justin

[GGR]

I did not use the engine shock absorbers on the Coupe conversion and I'm not planning to use them on the Pagoda conversion. I never really understood their function other than restraining the engine from bouncing around when hitting potholes (suspension pushes the axle carrier up which in turn pushes the engine up). This may be a problem on Pagodas as clearance with the hood is thight and there is a risk of damaging it. This is why there are stop plates mounted on the top of the axle carrier mounts. Using stiffer engine mounts like I will be doing may also help reducing engine movements.

Other than that I don't know where you can find 3.5 engine shocks. All the ones I've seen were shot and they cost an arm and a leg new.

Regarding the radiator, I would compare the capacity of the 280SL with the one of the 3.5. Put them flat on the floor, fill them with water and then compare capacity by emptying each in a bucket and measuring water volume. If capacity is similar, Which I belive it might be, I would just use the 280SL radiator. You may want to have it boiled and cleaned at a radiator shop and make sure the clutch fan is in good shape to contain overheating. You may have to swap oil cooler from left to right as all the piping is on the right on the 3.5. If you need to use another radiator, I would consider an r107 one rather than one out of a sedan, as the latter do not have the expansion tank system.

What engine mounts did you use?

How is your clearance between right exhaust manifold and steering box?

How is your clearance between alternator and metal sheeting around where the original air cleaner was located?

[justininia]

Good morning!
 
We've been busy over the past week trying to get some of the parts installed.  We've managed to get the steering column in, the wiring started, and the trim work begun.  As always, a few hiccups to slow proceedings down but we are gaining ground.

To answer your questions:
1.  The motor mounts are out of the 300SEL (I can't find the part number readily).  They are the squarish rubber mounts, a little lower in profile than the stacked cones the SL uses.  The arms are 116 and seem to hold things at a useable height. 
2.  Approximately 1.1 inches between the steering box and the manifold.  It's a little tight back in there and hard to take a good measurement but that is as near as I could get the caliper.
3.  We've not yet fitted anything in the space yet.  The metal shield is still out of the car and I've been contemplating reversing the bow of the metal.  That would enable us to keep a roughly Mercedes feel to the piece, protect the computer, and get the radiator mounted.  The air cleaner is going to sit on top of the engine so it shouldn't need as much space.  Just contemplating at this time.

The quest continues for the engine shock shock absorber brackets.  We managed to get a PN off the Mercedes EPC site and now it is just a matter of tracking them down.  When I have a moment, I will get some pictures of our progress uploaded for viewing.

Have a great week!

[justininia]

Good day to everyone.

Just thought I would drop a quick note on our progress.  We've gotten the steering assembly in all the way to the wheel.  If I make vroom vroom noises and turn the wheel back and forth, I can almost feel the wind in my hair.   

The wiring loom is getting placed and we are testing several items for fit - gauges, relays, lights, etc.  We got the convertible cover latches installed and working.  Some interior work has been done and a few of the carpet pieces put in for fit and appearance.  The brake calipers are all on with pads and rotors.  As a distraction we occasionally search through all the chrome pieces to see what is missing, what can be buffed, and what is going in for re-chroming.

Next steps:
1.  Figure out the accelerator linkage.  The engine sits fairly tight to the firewall.  Since the linkage pushes up first, then to the front of the car, a custom linkage is going to be needed.  We have a 300SEL to look at for determining fit but there is considerably more space in the engine compartment of that car.
2.  Transmission mount.  I've not gotten underneath to actually see this issue so I can't speak fully on the problem at hand.
3.  Drive shaft fitting.  The drive shaft is out for modification at the moment but when it returns we will install it and verify everything is in alignment.
3.  Finish the front and rear wiring.  The engine has several relay mounting brackets that need to be located in the compartment yet.  Since we moved the brake booster over, the bracket and relay set that fits into the space will need modified.
4.  Radiator fitting.  The radiator fitting is waiting until the radiator returns from being tested and repaired.  The oil cooler was sent in at the same time.  Once it's back, we will get the RH bracket fabricated and installed.
5.  Install the alternator, power steering pump, and AC components.  Then pray the hood closes. 
6.  Fix the heating and cooling controls.

It all seems like small stuff but it certainly takes up quite a bit of time.  I will try and update our progress as we make some.

Hope everyone has a great day.
Justin

[stickandrudderman]

Some pictures would be nice!

[justininia]

Here are some photos so far -

[justininia]

Good day, everyone!

A bit of a status update.  I've been busy occupying myself with a bit of speedometer and tachometer repair work.  We happen to have a 160 MPH speedometer for a 300SEL laying about and thought it would be fun to switch the guts into the SL housing.  Before I can do that, I had to repair the gearing that turns the odometer in the speedometer so it can be swapped with the unit that is geared correctly for the differential.  I'm still working on how to pull the needle without destroying it but everything should change over correctly with some minor modifications (like switching the position of the odometer gear and drilling a hole in the face for the turn knob).  It's going to take a call to Palo Alto to get a bit of the know-how before moving forward.

Got all the interior pieces upholstered trim pieces ready to go in the interim and a goodly portion of the chrome is out for recoating.

We are currently working on getting the drivetrain in alignment.  The transmission mount is sitting up a touch high and needs a bit of modification to get the right lines.  Out of the alignment, we have noticed that the fan sits about 4" above the radiator line.  I cannot foresee the hood closing in such a state.  One option would be to cut down the fan blades.  That would need to be professionally done and balanced again.  If anyone else has suggestions, fire away. 

I will try and shoot some pictures of the fan so the problem can be seen.

Have a great day!
Justin

[GGR]

You should fit the hood tentatively and see wwhere things fall. In my case the fan was too close to the hood with the 3.5 engine mounts. I fitted some lower mounts and clearance with the hood is now OK.

[justininia]

Good afternoon, everyone.

Update time for those folks following our progress.

In the past week, I have been working on replacing the rear wood deck (behind the seats).  Trivial compared to everything else but getting the hardware and the planks ready is just another task in the very long list still remaining.  After having built the mirror image of the actual pieces, I remade all the pieces and have them drying from the sealing process.  Hopefully that is wrapped up in the next day or two.

In positioning the engine, we ran across another issue - the drive shaft and transmission were striking the left side of the tunnel.  The engine could be pried over a little but not enough to make the parts clear the sides correctly.  Inspecting the lot turned up a problem with the front cross/axle.  The front we had came from a donor 280SE.  The part has what appears to be three degrees of twist in it, causing the engine to mount slightly crooked.  We've since taken that front out and have begun the process of fitting in one that is straight.  Not a fun way to spend time but it seems we are now moving in the right direction again.

We've also been fabricating a right-side radiator mount that is narrower than the original.  The new one should allow the computer to be mounted behind it and still maintain the stability and strength of the original. 

The gas tank is mounted and most of the wiring loom is now in place.  Other fun progress has been mostly in the interior, fitting gauges and dash pieces.  A lot had to go out for repair and dye work.  We've since been making sure everything fits and before too long expect to fit in the windshield (and its enormous gasket).  Lots of pieces also headed out for chrome work and now need to be installed or reassembled. 

The problem of fan clearance still remains and our solution will likely be to use a low profile electric fan, common in many modern cars.  Until we sort out the front axle issues and properly fit the engine, this issue won't be addressed.

I will get some more pictures for the folks interested after I get the radiator bracket installed.

Cheers,
Justin

[GGR]

3.5 left and right engine arms aren't the same length. Make sure you did not intervert tham as this will influence the position of the engine laterally speaking.

[justininia]

That was our first thought as well but the problem was a twisted cross.  We pulled it out and replaced with another one that measured better and everything is fitting better.  The driveshaft fits in the tunnel correctly now.

Now that the car is back to having the front, we are on to making linkages.  We have an automatic transmission in the car with the 290SL shifter assembly.  I think I found the wrong linkage for the car because when I get it lined up on the shifter, it goes about 4 to 5 cm past the bracket on the transmission.  It may be a matter of the gear the transmission is in (I haven't fiddled with it much.)

We've also been fitting some of the front grille pieces, prepping the parts that need re-chroming and polishing other parts.  The front bracket for the radiator is almost ready.  We need to do a little modification to the oil cooler but it is almost done. 

This week is the start of brake lines and some other fun work.  More posts with progress.

Cheers!

3.5 left and right engine arms aren't the same length. Make sure you did not intervert tham as this will influence the position of the engine laterally speaking.

[GGR]

You can turn the arm 180 degrees on the transmission so as to use the SL shifter with P at the bottom (the 3.5 one is in the top).

[justininia]

Ah, the holidays are a great time for getting nothing done...

We've been back on task since the start of the year.  The chores we've done are
-Fitting the fuel lines including running the line to the driver's side front or a fuel filter (similar to the placement on a 300SEL)
-Fitting the brake lines
-Running the rear wiring loom
-Building a battery brace to sit behind the passenger side shock tower
-Building a bracket to mount the computer next to the modified radiator bracket
-Mounting a vacuum unit to the firewall
-Cutting down the overflow tank bracket and mounting it to the firewall beside the wiper motor
-Working on re-installing the heating duct work and flaps
-Fitting the grille surround and the grille pieces
-Rebuilding the heater controls

Right now we have the engine out of the car and will be prepping for painting the engine bay.

I will try and post some photos of the recent modifications when I get a chance.

Justin