As I had the radiator off to work on the AC, I thought I would fix the leaking crankshaft front seal, so off came the timing cover. This is what I found. Clearly the tensioner and chain guide are pretty shagged.
What is uncertain to me is whether this timing chain has stretched beyond service limits?
OK, so the timing chain needs replacing? The next question is clearly about replacing the sprockets. Do we replace them automatically when we use a new chain? This is a closeup of a single tooth on the cam sprocket.
The wear is more visible with an isosceles triangle superimposed.
So what would others do? Re-use or replace? Answer on a $100 bill please.
If it were mine and I had a new set of sprockets to go along with a new chain I'd replace them. Why? For similar reasons that it's done on motor cycle primary and secondary drives when chains and sprockets are used. Sprocket teeth become hooked over time...also they shouldn't be pointy...as the pitch is affected. New chains tend to ride on top of old, worn and hooked sprockets, rather than the rollers properly sitting in and engaging with the sprocket teeth.
Thanks for the reply. So I need a new timing chain and large sprocket. The small ones are not available on Wadhams website. Also I noticed rather less wear on the small sprocket. Why? I asked myself, and now I am answering my own question.
First, here are enlargements of a single tooth from the large sprocket. Bearing in mind that the R edge is the side subject to wear, I am hard put to see any evidence of wear at all.
The answer: When chain and sprockets are new and unworn, they are of the same pitch. This means that under load, equal pressure is placed on every tooth that is engaged with the chain. The large sprocket has something like 48 teeth, of which around 36 are engaged with the chain. As the chain lengthens, there is an accumulative error in the sprocket-to-chain engagement that goes from something quite small on tooth one to 36x something quite small by the time the chain leaves the sprocket. This results in the bulk of the load being transmitted by only a couple of teeth, with the resultant large increase in load and wear rate on those couple of teeth.
The small sprocket in contrast has only 18 or so teeth engaged with the chain, and so the accumulative error only gets up to 18x. It is striking what that difference does to the measured wear rate.
Very good...you've succinctly answered your own question. Rover V8 owners are more fortunate as the timing gear (chain and 2 sprockets) are readily available either in OEM type (I picked up a couple of new old stock sets for $36 a while back) or super precise vernier adjustment totally steel sets for the serious rev head!