Pistons - availability?

[Erik]

Hello,

My engine, 127981-12-004430 (230 SL - 1966) needs a complete rebuilt.
I am looking for a supplier of pistons and valves and that seems to be a problem.

Can anyone recommend a place to order these parts at a reasonably price?

Thank you,
Erik
Belgium

[mdsalemi]

Erik,

I understand that the 230 SL pistons are anything BUT reasonable in price.  Check our vendor list.  The pistons for later engines are lower in price.  Whoever will sell you the pistons will sell you other engine parts as well.

[ja17]

Hello Erik,

Yes, unfortunately, Michael is correct. The parts for the 230SL engines are getting to be hard to find an very expensive.

The "good price" for the 230SL piston assemblies (pistons, rings, wrist pins) seems to be around $300 US per cylinder !! This is for original equipment.  Many places will quote higher prices.

Cylinder heads, and some crankshaft bearings are expensive and hard to find also.

Keep searching, you may get lucky and find someone with some NOS  at better prices.

[Benz Dr.]

There are three different pistons used on 230Sl engines but I suspect that yours would be the early version. If they've never been changed, I usually go by the casting number on the connecting rods. Standard bearings are not available and you have to go to .25mm or .50mm under size.
I believe early pistons are 4 ring with 24mm pin bushings. These are the flat top normal compression pistons. They're normally made just a little a bit shorter to compensate for machining ( decking ) the top of the block which is something we always do to true it up. The rest of the parts are generally available or used cores can be found if you have problems with anything you have.

[jacovdw]

Dan is correct.

There are essentially 3 versions of piston for the 230SL. However, you need to make a distinction between automatic and manual gearbox engines to determine the correct version.

Erik's engine number indicates an automatic gearbox variant with a serial number 004430.

That means that the engine calls for the 3rd generation piston.

If it is a manual gearbox variant, then it would call for the 1st generation piston.

Erik, have you tried SLS for the parts?

[George Des]

There were also at least two original manufacturers of these-Mahle and Kolbenschmidt. Best to shop around on these. When I got my oversized set for a rebuild 7 or 8 years ago, the prices varied greatly.

George

[Benz Dr.]

There are three different pistons used on 230Sl engines but I suspect that yours would be the early version. If they've never been changed, I usually go by the casting number on the connecting rods. Standard bearings are not available and you have to go to .25mm or .50mm under size.
I believe early pistons are 4 ring with 24mm pin bushings. These are the flat top normal compression pistons. They're normally made just a little a bit shorter to compensate for machining ( decking ) the top of the block which is something we always do to true it up. The rest of the parts are generally available or used cores can be found if you have problems with anything you have.

 Regardless of it being standard or auto it should still have the early version pistons in it because the VIN is quite early. I would NOT use the third or late version in it and would locate early connecting rods instead. The late pistons are the stepped type and they lower compression ratio considerably - maybe down to 130 PSI which would be rebuild time for normal pistons. I've seen flat top piston 127 engines run as high as 165 PSI so I'd be lookling only at those.

The only way to know for sure is to look at the connecting rod casting number and the size of the pin bushing. There were quite a few early version engines made, not so many mid engine versions and quite a few late versions. I'm not sure if the mid engine version piston is even available any more.

[UKSteve]

Well, this is an interesting thread. If I knew then what I know now.....

I rebuilt my 230 1967 block 2 years ago.
The shop re-bored to + 40 thou, and supplied me with stepped pistons. (Mahle)
I assumed this was to account for the extra volume as a result of the re-bore.
So I guess I've ended up with a low compression engine. hmm
(I'll have to get a compression tester to confirm)
Frankly, I just didn't know any better and hadn't discovered the forum at that time.
My cylinder head had been overhauled about 5000 miles earlier by Roger Edwards.

Question for Dr Benz:
Assuming I have low compression, do I just live with it, or are there some things I can do to improve the situation?
I've just finished a summer tour of the south west of the UK.
Over about a thousand miles of very varied terrain, I've averaged 23 MPG (imperial). Plug clour is good and the engine revs freely and smooth.
But significant hills really slow me down, and I suspect a lack of power (torque?)
Are the tuning specs the same for engines with stepped pistons?

Thanks
Steve

[Benz Dr.]

Your suspicions are correct. I have no idea why they went to stepped pistons as a re bore won't increase compression ratios all that much. You are probably down into the 8 to 1 area right now so you won't need premium fuel - regular will do just fine. I would throw all the ignition timing at it that you can. Maybe as much as 10 degrees BTDC and as long as the engine doesn't ping under load at low RPM's it should be OK.

  Start looking for an early set of connecting rods and pistons in the size you need. You can always use the old stepped ones for pencil holders at work.

[UKSteve]

Thanks Dr Benz, Its good to have some clarity.
Maybe my "relatively" good fuel consumption is a consequence of lower compression?
I'm looking forward to trying out some significantly advanced ignition.
I'm wondering if it would make sense having the head skimmed to resore some of the lost compression?
Much easier than piston replacement, even if I could locate flat tops in the right size.
Thanks
Steve

[Benz Dr.]

Never cut a cylinder head for any reason unless you have to. I imagine your better mileage is due to no loss of compression and not so much lowered compression.

 Early connecting rods are out there and all early pistons are flat top. Whether or not the size you need is available should be your first enquiry. If you find them then you can start looking for early connection rods. The pistons are going to be your more important consideration because if you can't find any then it's all moot.

[Cees Klumper]

Dan - how about an alternative to cutting the head: adding some metal to the combustion chambers to increase compression? No idea whether this would work (welding aluminum is more difficult so I understand) but in theory this would work and avoid the necessity to buying new pistons and connecting rods?

[merrill]

Metric Motors could also be a source for parts.

http://www.mercedesengines.net/

[badali]

Would a 220 or 230 sedan have the same pistons?

[ja17]

Hello,

Start off by checking your compression first.

[UKSteve]

Hi Doctor and others,
Just by way of feeding back and tying off this thread:
I got hold of a compression tester. Your guess was 100%.
I have 127 lb. ( 3500 miles since rebuild)
I advanced the timing by 10 degrees as suggested. I sensed the motor felt more responsive. I had no indication of pinging, but the landscape is pretty flat where I live so getting under load in top isn't that easy. Thanks for your advice. I don't know how much power I might be missing out on, but I think I'm probably optimised for now pending some major surgery.
Thanks.
Steve

[stickandrudderman]

If I want to test a car for pinking I park it with the wheels against an obstruction, handbrake on, toe and heel the brake/accelarator, engage gear and try to drive off with as much throttle as I can without overcoming the restraints. It'll pretty soon pink under those conditions if it's going to at all.
Incidentally, oil contamination of the combustion mixture, especially from worn valve guides/seals, will accelarate the onset of pinking. I've seen many cars where the timing has been backed off by other garages in an attempt to cure pinking without an understanding (or, if I'm being generous, with an understanding) of the route cause. Try not to loose control if you try this at home!

[Benz Dr.]

127 PSI is actually pretty low. Try adding a bit of oil to that cylinder and see if it raises at all. A little would be normal and a lot would indicate something wrong with a piston. No rise at all could indicate a leaking valve. You should have about 150 PSI with stepped pistons.

 I wouldn't try anything '' clever '' in the combustion chambers or try anything that would destroy the head. Blocks are generally available but heads aren't.

[UKSteve]

Ok, I'll try some oil in the bores.
Perhaps I should have mentioned that it was a dry test, a cold engine, and a simple tester that resembles a pencil type tyre pressure gauge.
Steve

[ja17]

Hello,

Compression check should be done on a warm engine with the throttle open. Use a good tester. Defective compression gauges are not uncommon.  They suck in carbon and foul up the works.

[Benz Dr.]

You know, it's not very often I would disagree with Joe because he knows a lot about these cars but I think I might this time.

I agree that compression gages will get full of carbon and quit working properly - no argument there. I might even agree with doing the warm compression check, although I rarely ever do, and for a good reason I might add. But I will disagree with having the throttle open on a 113 engine during the test - if anything you want it closed.

 You don't need to have it open. On some cars, yes, it's the only way you can get a reading but on our stuff it makes zero difference. The engine will idle with the throttle fully closed which is how it's supposed to work so there's more than enough air entering to get a full reading.

And that's why I do the compression test on a cold engine. The warm up device should be fully opened which will allow extra air to enter the cylinder. If there wasn't enough air the engine would not run or start.
 If you try to start your engine from cold that's when poor compression will cause difficulties getting it to fire. I want to know what I have for cold starting - the more it's at optimum compression the better it will work. A warm test is usefull but I figure if I have enough for cold starting it will be OK for hot starts as well.

[ja17]

Ok Dan, I see your reasoning on this. We therefore can deduce that a correct reading can be had with or without the throttle open !