Another broken chain rail

[RaceDiagnostics]

Well after hearing an odd sound for a few seconds last time I started the engine, I thought I had better investigate. Since I have all the parts for a full chain, guide, tensioner replacement gathered for my old engine, I thought I would go all the way and do the full job.

I expected that the sound was chain rattle on the heads due to a weak tensioner.

But I was wrong..... if you have one of these old engines you should have look at yours.

 

[Alex Crow]

Yup, they do that!
And it can be any of the 3x top end rails, less likely to happen to the tensioner rail (which can also be changed without front case removal), and pretty much never happens to the lower rail (hidden in the lower timing case area, engine out job to change).

I suggest a new tensioner, and the 3x new top rails, if this has not already been done (and the chian as well, but looking at the pics it has been recently changed).

Looking at your broken rail, it has fractured at the thin side of the location pin, before finally breaking across the thicker side.

 

[RaceDiagnostics]

I got the three new rails fitted as well as putting a new cap on the tensioner rail. Getting the pin back into the bottom of the tensioner was a pain and took a lot of trail and error but it finally went in.

Tomorrow I will feed through the new chain, and get it all put back together. The new tesnsioner is sitting in a bath of oil so will be good for the morning.

I need to remember to measure the length of the new chain to compare to the old to see how much it has stretched.

As the engine was bought from ebay a year ago I have no idea of the age or mileage of either the chain (it is definitely a replacement as it has a removable link) or engine. I was pleased to see all the spark plugs were clean and dry though.

 

[RaceDiagnostics]

This morning’s work.

Old chain linked to the new.

After a lot of zip lock ties, the new chain emerged and linked up to the other end.

And now to check what the stretch was............... a measly 4mm, well that’s that done for the lifetime of the car, (in my ownership anyway).

These are the before and after pics of the timing mark with the cylinder 1 CAM marks lined up, the timing has been pulled in by about 7 degrees, so I am pleased with that. New on top old below.

 

[Dieselman]

That's a fair bit of chain stretch to have allowed 7 degrees of timing retarding, good job, well done.

Changing the chain is supposed to be easy and only a few minutes work, with no cable ties at all.
Link the chain, grab both free ends and have a helper wind the starter motor. You keep the chain tight over the cam sprocket and keep pulling the excess away as it feeds out.

See...easy..

 

[grober]

Plastic components will eventually lose their plasticiser content with age [ accelerated with heat?]and become brittle. I can only suggest the lower rail is perhaps subjected to less heat stress being lower down the engine as an explanation.

 

[Alex Crow]

Changing the chain is supposed to be easy and only a few minutes work, with no cable ties at all.
Link the chain, grab both free ends and have a helper wind the starter motor. You keep the chain tight over the cam sprocket and keep pulling the excess away as it feeds out.

See...easy..

Nice one DM, love to see you do that on this V8 engine - hopefully a joke?^

 

[Dieselman]

Nice one DM, love to see you do that on this V8 engine - hopefully a joke?^

It was, but the Yanks claim to do it this way regularly.


As long as you don't let that chain go loose on the first cam, you're home dry.

 

[Alex Crow]

Easier said than done, and I have changed plenty of chains on both 116 and 117 engines, both old and very old!

Not recently though...

 

[Ponton-Jetronic]

Big thank you to both Race Diag and Alan C for the tips on timing chains and their operation, how-to etc.[And the pre priming of tensioner before fitting].
___________
Ponton-Jet.