W124 Idiotic mistake. Missed timing chain cover bolt when lifting head and... 'CRACK'

[optimusprime]

Well the bonded repair might be good to go for now But if the repair comes away , the only place the broken part can go is down . Then it will mean your looking for a complete new engine .The part will fall in to the timing chain that in turn will jam up the works for good . Do it right once .

 

[Will]

That,s pretty damn thin! As Will said the major stress to any bonded repair will be replacing the chain guide retaining pin which is an interference fit afaik

Yes my thoughts exactly. The moment that chain guide pin is refitted that crack will split straight open. The cost of a gasket set and head bolts etc is dwarfed by the inconvenience of having to do the job twice!

You have to physically hammer or press those pins into place, so not sure how well glue will hold this with the sideways force against it. Likewise the pin will act as a wedge and will surely just split the crack right open anyway.

That used head for £150 from MSL is decent value. I can’t understand why the existing head has been skimmed before it was repaired - sorry!

 

[Dickster]

Yes my thoughts exactly. The moment that chain guide pin is refitted that crack will split straight open. The cost of a gasket set and head bolts etc is dwarfed by the inconvenience of having to do the job twice!

You have to physically hammer or press those pins into place, so not sure how well glue will hold this with the sideways force against it. Likewise the pin will act as a wedge and will surely just split the crack right open anyway.

That used head for £150 from MSL is decent value. I can’t understand why the existing head has been skimmed before it was repaired - sorry!

Exactly, repair it then skim it .

I’d probably repair it if possible, and find a replacement head as a back up at least….

 

[optimusprime]

Do any job right ,,and forget it . Or repair it with plastic weld , and keep thinking about it every time you drive the car weather it will stay put or not and you have to get a tow truck to get you home .

 

[RogK]

I know it's far from ideal, but for better or for worse, I jb-welded the front, got it flat and everything lines up. I figure if the repair stands up to hammering the pin in, it should be good for holding the guide rail.

I asked the welder who looked at it about vibration and he reckoned if its not enough to crack a plastic guide rail it shouldn't be too much strain on the bond? not that he'd swear by it. Most of the bore is still on the main body.

I'll give it a go. If it fails, I'll take it on the chin; if it works it gives me some time to figure out a proper replacement. I'll get some pics up later

 

[Bellow]

Can you post some photos of the bolt that passes through the fractured boss?
Does anyone know why it is an interference fit at its external end? (I'm assuming photos will show a shoulder at its internal end that determines when it is 'tight' and therefore the bolt when torqued is not in tension).

 

[Will]

There’s a bolt that screws down from the cylinder head into the block - I reckon the one he missed was by the coolant temp sensors etc?

The pins for the plastic guide rail are the interference fit ones, they push into the head from the front of the head backwards - they are only held in place by friction, they will need punching in and are usually pretty tight to remove.

 

[Will]

You can see the pins on this link, and how they locate (item #101 on the second image):

MERCEDES M102 Engine Timing Chain Guide Rail Pin A1020520174 for sale online | eBay

Find many great new & used options and get the best deals for MERCEDES M102 Engine Timing Chain Guide Rail Pin A1020520174 at the best online prices at eBay! Free delivery for many products!

www.ebay.co.uk

 

[Bellow]

There’s a bolt that screws down from the cylinder head into the block - I reckon the one he missed was by the coolant temp sensors etc?

The pins for the plastic guide rail are the interference fit ones, they push into the head from the front of the head backwards - they are only held in place by friction, they will need punching in and are usually pretty tight to remove.

Got it now - and remember them from rebuilding my smart's engine.
Not threaded at the other end (the only thread is an internal one to aid removal).
Had it been threaded at the other end I might have suggested a little relieving at the boss but without a thread at the other end to retain it - not viable.
All I can think of to improve it's chances are bolting a plate across the mating surface using the adjacent bolt holes while pressing it in (before the head is on the block obviously) to help hold the fractured part close. Any sign of the pin having loosened when the plate is removed would suggest the joint has split.

 

[RogK]

The bolt that led to the whole sorry story is not the bolt by the sensors, it's one of the three spline head bolts at the timing chain cover - the one that is slightly obscured by the timing chain guide as you're looking down the line of the timing chain.

Bellow, as it happens I did plate the repair with a bit of aluminium the welder guy had lying around, but only the flat faces.

I'll see about doing something similar around the damaged bore. The pins came out relatively easily using a puller rigged up with a socket a bolt, washers and a nut or two.

When I did the head gasket and timing chain on my 190D, I remember having to drill a guide pin out, which left the replacement pin as a looser fit. At the time I used gasket sealant or similar on the end of the pin when reinstalling it and it sealed it fine. Hasn't been a problem in 100,000 miles!

In work right now, will post some pics of the state of play when I get home this evening.

I'm very grateful for all the input, cheers everyone.

 

[Bellow]

Bellow, as it happens I did plate the repair with a bit of aluminium the welder guy had lying around, but only the flat faces.

I was going to suggest that too - but was kind of discouraged by the contoured surface - but you managed some reinforcement.
What I was meaning though was to temporarily fit a bracing plate above where the boss is, across the mating surface of the timing cover part of the head using the bolts (one of which got missed and cause the grief) to pull down on the fractured part to minimise the chances of the joint separating while fitting the pin. There are bolt holes that would permit a plate across the corner above the boss. Once the pin is in, the plate can be removed, discarded and the head refitted to the block.

When I did the head gasket and timing chain on my 190D, I remember having to drill a guide pin out, which left the replacement pin as a looser fit. At the time I used gasket sealant or similar on the end of the pin when reinstalling it and it sealed it fine. Hasn't been a problem in 100,000 miles!

.

There's always the possibility of fabricating a retainer plate and bolting it up through what appears to be a coolant port that has two bolts.

 

[Will]

The only trouble is, you need to remove that plastic guide to get the head off without cutting the chain. There’s no split/removable link - so it would involve cutting the chain and realistically a new chain plus riveting tool (or peen the link over if you know what you’re doing!)

 

[RogK]

I was going to suggest that too - but was kind of discouraged by the contoured surface - but you managed some reinforcement.
What I was meaning though was to temporarily fit a bracing plate above where the boss is, across the mating surface of the timing cover part of the head using the bolts (one of which got missed and cause the grief) to pull down on the fractured part to minimise the chances of the joint separating while fitting the pin. There are bolt holes that would permit a plate across the corner above the boss. Once the pin is in, the plate can be removed, discarded and the head refitted to the block.

There's always the possibility of fabricating a retainer plate and bolting it up through what appears to be a coolant port that has two bolts.

Food for thought. Nice one.

 

[grober]

Other option would be to turn down the retaining pin diameter slightly so that it wasn't an interference fit-- pass it through chain guide and JB weld it in place- if it's good enough to hold casting together it's good enough to hold a pin in place? If determined to press it into place might be worth sticking it- the pin-in a freezer overnight?

 

[Bellow]

The only trouble is, you need to remove that plastic guide to get the head off without cutting the chain. There’s no split/removable link - so it would involve cutting the chain and realistically a new chain plus riveting tool (or peen the link over if you know what you’re doing!)

I missed that - well spotted!

 

[RogK]

Here's how we're looking right now.

 

[RogK]

Other option would be to turn down the retaining pin diameter slightly so that it wasn't an interference fit-- pass it through chain guide and JB weld it in place- if it's good enough to hold casting together it's good enough to hold a pin in place? If determined to press it into place might be worth sticking it- the pin-in a freezer overnight?

I was thinking about achieving the same end by different means and using a small round file to ever so slightly increase the diameter of the hole, then as you say, fit the pin and epoxy it in

 

[Bellow]

I was thinking about achieving the same end by different means and using a small round file to ever so slightly increase the diameter of the hole, then as you say, fit the pin and epoxy it in

If you open up the boss a touch, then that preserves any interference fit available at the other end.
A piece of emery paper wrapped around the shank of an appropriately sized drill bit and worked by hand will probably be all that's needed and help maintain roundness compared to using a file.

Never having worked with JB my comments may be unwarranted but I wouldn't use it to secure the pin as I imagine it to set hard and if from the very thin film present in the boss any broke loose then it would enter the engine and, allow the pin to become loose and possibly fall out.
I would use RTV (applied to the last 1/2 inch of the pin before pressed fully home) and back it up with a fabricated plate butting against the pin's end and bolted via existing bolt provision.

Good RTV (eg Dirko) is very adhesive and absolutely will not crack with vibration in the manner I fear the JB could. Only a suggestion though and if there's a flaw in it, someone will surely make it apparent.

 

[RogK]

If you open up the boss a touch, then that preserves any interference fit available at the other end.
A piece of emery paper wrapped around the shank of an appropriately sized drill bit and worked by hand will probably be all that's needed and help maintain roundness compared to using a file.

Never having worked with JB my comments may be unwarranted but I wouldn't use it to secure the pin as I imagine it to set hard and if from the very thin film present in the boss any broke loose then it would enter the engine and, allow the pin to become loose and possibly fall out.
I would use RTV (applied to the last 1/2 inch of the pin before pressed fully home) and back it up with a fabricated plate butting against the pin's end and bolted via existing bolt provision.

Good RTV (eg Dirko) is very adhesive and absolutely will not crack with vibration in the manner I fear the JB could. Only a suggestion though and if there's a flaw in it, someone will surely make it apparent.

Good call there. Is Dirko the Elring stuff? It sounds familiar. I think when I picked up the head gasket set they threw in a tube.

 

[BigJase88]

Looks a bit Heath Robinson

Would of 100% got it tig welded

Would of been a easy job for a decent welder