TR4/4A timing chain and sprockets

Hi all,
The timing chain tensioner broke on my tr4a, quite a bit of racket. How can i tell if the chain and sprockets need to be replaced or not. Also how do you tell if the chain is to tight or to loose. thank you grant

It's hard to tell with the chain on the engine. But if you remove it, hold it sideways in your fingers, so the chain sticks out horizontally. It should have very little "droop" (flexing sideways). If the droop is significant, then it's due to be replaced. I was taught to replace the chain and sprockets as a set, since they wear together in service. Putting a new chain on worn sprockets will cause rapid wear in the chain.

That said, TR chains & sprockets seem to last a long, long time. I'd be seriously tempted to just replace the tensioner and let it go. In fact, that's what I did when it broke on my previous TR3A, even though it's a lot more hassle to get to the chain on a 3A. Not sure how many miles that engine had on it, but I put probably 200,000 more on.

As I recall from when I replaced my tensioner, the manual has a spec for the free play in the chain (how far you can press it in). You might also take a look at that.

Mine (unknown mileage) was within the spec and seemed okay (what do I know?) so I stayed with it.

I recall seeing a spec for free play too. Seems like it was a measurement from a stud to the chain with the chain "compressed". Since all I have is a Haynes manual it may have been in it. I recently switched out short blocks and checked both engines. It was considerably less distance on the "new" one and the tensioner had only very light marks from wear. The older engine had significantly more play in the chain, more wear on the tensioner, but ran fine except for the crack in the block. I'm with using the chain as is unless you find some significant wear, or just want to tighten up a little while you at it. Seems the parts were not that expensive. Could be one of those "while I'm at it, for peace of mind" things.

Hi,
I checked the chain slack and it is 9mm. I found a site with a diagram. Apparently 10mm is the max. The sprockets seem to have a small amount of wear. I am going to leave the chain and sprockets as is.
I do need a chain tensioner. Is stronger or upgrade tensioner available for sale. Thank you grant

I don't recall seeing any stronger alternatives when I needed one. On the other hand, the original probably lasted 100,000 miles.

Check the cover too. The tensioner ofter wears a groove in the cover and occasionally the front plate. I'm not sure if that is really a problem (until it leaks) but I replaced my well worn cover. Tom

TomMull said:

Check the cover too. The tensioner ofter wears a groove in the cover and occasionally the front plate...

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Mine wasn't too bad but I have heard of them wearing right through the side of the cover.

First engine I ever tore into was on my old TR4A many many years ago, knew it needed pistons and liners and a valve job, didn't know enough to even check the timing chain and tensioner, it had worn through the tensioner and wore through the cover right as I was leaving for my first trip to the vintage races at Road America. Lesson learned the hard way.

Anywhoo, I was gonna say chains are cheap and I usually just replace them while in there, but looks like they have gotten a little more expensive, so maybe it is better to do some of the tests already mentioned. If the teeth on the gears are sharp and pointy that is a sign they are worn. I have sometimes just replaced the smaller crank gear, my cheap mechanic rationalization being it is smaller so the load is more concentrated, plus it is usually cheaper than the big one on the cam. By all means always replace the tensioner, they are cheap and do wear out.

grant tr4a said:

Hi all,
The timing chain tensioner broke on my tr4a, quite a bit of racket. How can i tell if the chain and sprockets need to be replaced or not. Also how do you tell if the chain is to tight or to loose. thank you grant

Click to expand...

Did you get all of the pieces of the old tensioner out. I tore down an engine that was sidelined by that same thing happening. I found metal pieces in the oil pan.
Charley