R129 500SL Engine Rebuild

[Adamki95]

Hey Guys,

Ive been a part of the forum for years but I’ve been dormant the last couple years so I can’t get into my original account!

Basically we have a 1992 500SL in baby blue I’ve met some of you guys before.
Unfortunately recently we’ve had quite a big problem with our R129, my dad was driving the car perfectly normally him and his partner pulled over to look at something switched the engine off to look at something got in 3 minutes later and wouldn’t turn over it just “clunked” over.
Initially he tried to start it not thinking it wasnt anything too serious given that these cars suffer from major electrical degradation on the wiring harness.
Anyway no good so it was recovered to a garage who changed the starter motor and this didn’t solve it same issue still. This garage my dads used for years but doesn’t do complex repairs just a normal garage I went there and we manually turned the crank round with a ratchet while I looked at the camshaft through the oil filler cap and put my finger on the camshaft for any movement and there was nothing so big red flags at this point.
It looks as if the Cam chain has gone so it’s since been recovered to a Mercedes specialist where they have partially taken it apart and can confirm it’s the chain. They are smoke testing it on Monday to confirm how many valves are damaged but they think is most likely all of them which I’m not really surprised about but they’ll confirm that on Monday and of course naturally the heads have to be skimmed too. They said it’s very unlikely it’s cracked the heads as there’s no signs of fatigue or overheating so that’s some good news I guess.

The overall cost of this if it’s a full set of valves (32) it’s going to be circa £6,500 to £8,000 for this rebuild my dad will probably do it because he absolutely adores the car.
I discussed an engine replacement with the garage and they said that is definitely another option however there is still the concern of the timing chain failing and another good engine will cost £2k - £3k to buy anyway.

Just want to know if anyone else has gone through this heart ache and maybe open to suggestions at if there could be a possibility of an engine “upgrade” it’s a shame though because looking at the engines design it does look very much ahead of its time and a very very impressive unit.

Car is on 145k miles
And on a J reg
Image attached of the car!

Thank you all!

 

[NJS5]

Welcome Adamki95

Your profile is incomplete - whereabouts are you?

Good luck.

NJSS

 

[star]

Chains rarely break, but the guide rails do and can stress the chain. Here a bit of rail stuck in idler gear.

 

[LostKiwi]

I'd be surprised if it was more than a couple of valves given it was on restart that the chain let go.

For comparison I had a V6 Essex Capri which had a timing gear fail. At the time it was doing 3000 rpm and it bent 9/12 valves.

How many miles has it done? Asking as mine has 145k....

As for engine upgrade the only one I'd consider is an AMG upgrade to the M119. The M119 is arguably one of the best petrol engine Mercedes made.

 

[toby1]

Rotten luck, I thought the M119 was fairly bulletproof.

I'd be looking to buy a shed and have the motor out.

 

[Adamki95]

I think what they meant it was chain related, I completely forgot to ask specifically. When I speak with them on Monday I’ll ask.
They can’t confirm weather it has done all valves they can only at this point assume the worst until the smoke test is completed.
It is a really rotten bit of luck to be honest car has covered 146k miles and has always been reliable and never ever shown signs of failure.
In many ways it would feel so wrong to break it for parts.
An engine swap to something exciting could be on the cards depending on what could fit because the cost could really start to run away.
If it’s potentially going to cost £8k to fix then surely an engine swap wouldn’t be completely ridiculous?
Either way I think it’s right to keep the car on the road.

 

[LostKiwi]

Pardon our interruption...

www.ebay.co.uk

Get it, change guides and chain and all sorted.

 

[Adamki95]

Bad news I’m afraid.
Engine is beyond repair and not worth saving the timing gear on the right hand bank camshaft snapped off causing a bit of mayhem it’s damaged the cylinder head the vales and obviously the camshaft.
@LostKiwi that engine looks like a good option seems like these engines are hard to come by….

 

[Adamki95]

My dad’s heading to the garage tomorrow to see for himself.
Could be a possibility we may do an engine rebuild or the replacement ourselves after all we are an engineering company and have made all sorts of parts for classic cosworth racing engines at this point we don’t really have much to loose.
My dad and I both agreed it would be a crying shame to sell it for parts…

 

[SL63 Mark]

Sorry to hear of your woes, it really is a beautiful car. Not sure if that is an original MB colour ? It really is special. So worth saving. I hope you can find a suitable engine soon. I would like to see some photos of the interior ? I think you won't know about the engine until you get it apart, it is all speculation. Once you have it apart I suspect you will want to replace everything anyway, at that mileage. The problem will be availability of parts. Keep us up to date with whatever you decide to do.

 

[Adamki95]

Car gets delivered back to the house on Monday.
In it’s current state so partially taken apart, we will start stripping it top down and see what parts exactly need replacing we know for sure a camshaft needs replacing as the timing gear on the end snapped off. if the issues run too deep then it’ll be sold as spares which is a shame but even with putting in another used engine it’s still going to cost between 5-7k (price including engine) not to mention these cars have the biodegradable wiring harnesses so it could potentially disturb those and lead to even more repairs if changing the engine.

 

[00slk]

Sorry to hear about the problem with the engine.
We gad a timing chain break in a w116 450 engine while it was idling and warming up for an oil change. The engine made a funny noise and stopped. We discovered it was the timing chain. Long story cut short. Fitted new sprockets, chain, and tensioners, restarted the engine. After a service and all was fine. The boss said, luckily the car was idling and not been driven by us, that would have been expensive!!
I would have thought the damage happened while driving for the engine to stop and not restart.
I guess the later V8's had more clearances than the 70's V8's.

@LostKiwi Has the idea

 

[Wighty]

Car gets delivered back to the house on Monday.
In it’s current state so partially taken apart, we will start stripping it top down and see what parts exactly need replacing we know for sure a camshaft needs replacing as the timing gear on the end snapped off. if the issues run too deep then it’ll be sold as spares which is a shame but even with putting in another used engine it’s still going to cost between 5-7k (price including engine) not to mention these cars have the biodegradable wiring harnesses so it could potentially disturb those and lead to even more repairs if changing the engine.

Wouldn’t mind seeing some pics of your work/dismantling progress buddy .
Good luck with it all .

 

[Adamki95]

I’ll certainly keep this thread updated.
It maybe a quite a while between posts as this will be fitted in between very busy work schedules!
.

 

[LostKiwi]

Car gets delivered back to the house on Monday.
In it’s current state so partially taken apart, we will start stripping it top down and see what parts exactly need replacing we know for sure a camshaft needs replacing as the timing gear on the end snapped off. if the issues run too deep then it’ll be sold as spares which is a shame but even with putting in another used engine it’s still going to cost between 5-7k (price including engine) not to mention these cars have the biodegradable wiring harnesses so it could potentially disturb those and lead to even more repairs if changing the engine.

If you can do the work yourself I can't see £5-7k.
In its quickest fix it's the cost of the new engine plus a set of guides though if that mileage on the one I found is correct it wouldn't need them yet.
Also yours from memory is a 92 with the mechanical fuel distributor. As I understand it it's the 93 without the mechanical fuel distributor that has the wiring issue (like mine). Rebuilding the loom is no big deal. Sileck do rebuilds for about £300-400 from memory.

 

[Richard Moakes]

If you can do the work yourself I can't see £5-7k.
In its quickest fix it's the cost of the new engine plus a set of guides though if that mileage on the one I found is correct it wouldn't need them yet.
Also yours from memory is a 92 with the mechanical fuel distributor. As I understand it it's the 93 without the mechanical fuel distributor that has the wiring issue (like mine). Rebuilding the loom is no big deal. Sileck do rebuilds for about £300-400 from memory.

You are right, the M119.960 CIS-KE engine didn’t have the the wiring loom issue, at least my 1991 car didn’t have the problem.

 

[Adamki95]

Here is the picture of the damage.
Note the broken camshaft is on the right bank.

 

[LostKiwi]

How are the valve clearances? If the clearances are large it suggests a bent valve. If they're ok you might have been lucky.

Do you know which chain guide(s) broke?

Also yours is as I thought the earlier mechanical injection which doesn't suffer the biodegradable wiring harness issue.

 

[Snake Charmer]

The question is what caused the camshaft to break? Looking at those photos, the broken camshaft does not seem to have stayed static as the other half attached to the sprocket has no signs of rotating against it. I would take all the camshafts out and see if they run true, inspect the cam bearing surfaces and caps for damage to see if valves have been pushed up bending the camshaft causing the breakage. Split the chain and remove it then do a leak down test on each cylinder at TDC to get an idea on the valves and pistons.
The camshaft lobes look almost new at that mileage showing a well looked after engine and might be worth repairing if the bottom end is good.

 

[Adamki95]

How are the valve clearances? If the clearances are large it suggests a bent valve. If they're ok you might have been lucky.

Do you know which chain guide(s) broke?

Also yours is as I thought the earlier mechanical injection which doesn't suffer the biodegradable wiring harness issue.

I couldn’t see much at the time but when I looked it looked as if second from rear set of lobes where in a fully down position on top of the valves and I couldn’t see much if any clearance on that section the rest looked fairly clear as in valves looked like they were retracted.
Sorry if that was a really amateur way of explaining things hopefully I’ll build some fairly extensive knowledge along the way!

Thanks for the info very useful to know!