Engine Timing

[Caleb Stovall]

So I know how to change a timing belt / chain and set the timing correctly and I also know how to set the timing of the spark using a timing light.
What I don’t know how to do is tell the difference on which is having trouble or how to diagnose a bad belt / chain without actually draining the oil and removing the cover to look at it.
I mean at the moment all I have to go on is being highly suspicious that the chain has stretched and skipped a link.

Topic

[Greg]

Are you working on a specific vehicle or is this a general question?
On older vehicles you could take off the distributor cap and turn the crank bolt and see how much play you had between the distributor in relation to how far the crank moved. Some of the newer vehicles have a cover you can remove over the tensioner to see if the tensioner is all the way extended and some you get to go all out and remove the covers.

[college man]

This may help.

https://www.ericthecarguy.com/engine-videos/705-how-to-check-timing-chain-slack

[Caleb Stovall]

That video helps a lot thank you college man.
Although that only addresses a stretched chain, what if it is a belt that isn’t tensioned properly that has skipped over a notch?

The engine that brought it up is on a 92 Chevy S10 but I work on a variety of vehicles, most overhead cam engines so this would fall under general information.

[Alexander B]

The only way I’d know is to use the specific tools (if required) to set the engine to its timing marks, and see if they all still line up. Some engines only need a locating peg in a hole, others need special tools, others again have clear visual markers, etc..

I had my timing belt off by a tooth once, the engine was down on power by a large amount (as in: it felt sluggish and felt like it had less than half its rated HP), so that might be an indicator?

[Caleb Stovall]

So on that’s pretty easy on my B18C1 because I can just taking the valve cover off real quick and check the marks.
An OHV engine requires a bit more work to get to the chain.

I’m guessing it’s one of those things that after you see a vehicle that slipped timing a notch, you’ll just “know” that’s the problem.

I really like the advice for checking the timing chain by rotating the crank backwards.

Do you think the same advice would work on a belt?

And you mentioned special tools or sticking peg in a hole….would these be for checking the position of the cam on an OHV engine?

[Alexander B]

I was thinking of belt driven (D)OHC engines, since thats what I see most.

On the TU and XU series engines (CItroën, Peugeot) you put simple pegs in the flywheel and in the cam belt gear(s) to locate the timing. No need to even open anything (except the plastic upper timing belt cover, which is held on by 2 bolts.)

On the Renault K4J/K4M (and a bunch of others) you use a special flat tool to line up the slots in the cams, and a specific length pin to locate the camshaft. I really don’t like how this engine used un-keyed timing gears, but thats another story.

I know some engines (GM?) there is a special shaped plate you bolt down over the camshaft lobe to hold it in the correct orientation, Of all these, thats probably the most expensive special tool. 😛

As you said, I think chain driven engines are much harder because the chain is usually under a sealed cover and/or buried quite deeply.

As far as rotating belt engines backwards to check, well, if there is enough slop to be noticeable its probably in serious trouble. on the other hand, belt driven engines usually have a simple plastic cover, so you can just check visually and/or by feel to see if the belt is tight.

[Caleb Stovall]

Great information.
Thank you. This gives me enough information that I know what to look for to learn more about it.

[Author]

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