Timing mess

[monkeyboy]

Fitting a new timing chain... more later if ever I get it working again.

Split the chain, connected the new to old and rotated the engine to feed through then reconnected the 2 new ends together. Marked the sprocket arrow on a particular link before I did it then repositioned it the same link on the new chain - it does make sense honest!

Anyway - I don't think its worked out right and I can sort of see why not but would like to ask a few basic questions to work out where I've gone wrong, then hopefully work it back out.

Now for the numbers. The cam sprocket has 17 teeth. I've counted them lots of times but I'm still willing to admit I might be wrong.

The timing chain has 84 links. 17 does not go in to 84 (85 it does) exactly.

Also, the cam rotates once per 2 rotations of the crank (doesn't it?) but how can it do that with an uneven number of teeth? ie the sprocket on the crank must have 8.5 teeth for that to work?

Also - the manual says the key in the sprocket is supposed to be up for TDC compression on the left...but... that position ALWAYS has the exhaust valves open.

When I fed the chain over as I rotated the engine, it went through an uneven number of strokes (5 probably) which is why my left is currently on the exhaust stroke.

Got to put this right! I will rotate the engine once more to get exhaust on the right and therefore TDC/Compression on the left then see what gives.

Questions are - how does this 17 into 84 thing work?

If I'm at TDC/compression on the left, what marks can I use to ensure the cam is correctly set?

All answers, condescending included, gratefully received.

 

[Timolgra]

If I'm at TDC/compression on the left, what marks can I use to ensure the cam is correctly set?

Look through the inspection cover, the two arrows should be horizontal.

 

[monkeyboy]

Look through the inspection cover, the two arrows should be horizontal.

That's what I thought. I just have to set it that way and rotate the engine a few times to check all the moving parts keep away from each other.

 

[nick.ct]

Fitting a new timing chain... more later if ever I get it working again.

Split the chain, connected the new to old and rotated the engine to feed through then reconnected the 2 new ends together. Marked the sprocket arrow on a particular link before I did it then repositioned it the same link on the new chain - it does make sense honest!

Anyway - I don't think its worked out right and I can sort of see why not but would like to ask a few basic questions to work out where I've gone wrong, then hopefully work it back out.

Now for the numbers. The cam sprocket has 17 teeth. I've counted them lots of times but I'm still willing to admit I might be wrong.

The timing chain has 84 links. 17 does not go in to 84 (85 it does) exactly.

Also, the cam rotates once per 2 rotations of the crank (doesn't it?) but how can it do that with an uneven number of teeth? ie the sprocket on the crank must have 8.5 teeth for that to work?

Also - the manual says the key in the sprocket is supposed to be up for TDC compression on the left...but... that position ALWAYS has the exhaust valves open.

When I fed the chain over as I rotated the engine, it went through an uneven number of strokes (5 probably) which is why my left is currently on the exhaust stroke.

Got to put this right! I will rotate the engine once more to get exhaust on the right and therefore TDC/Compression on the left then see what gives.

Questions are - how does this 17 into 84 thing work?

If I'm at TDC/compression on the left, what marks can I use to ensure the cam is correctly set?

All answers, condescending included, gratefully received.

The number of links in the chain has nothing to do with it, its the number of teeth on the sprockets that counts

 

[monkeyboy]

The number of links in the chain has nothing to do with it, its the number of teeth on the sprockets that counts

I just worked that out as I sat on the couch! What an idiot! Thing is - I 'assumed' the chain links was an exact multiple of the sprocket's teeth when I reattached the sprocket, and hence the wrong rotation. What a tosser Still, I'm sure it'll be fine now.

Thanks

 

[DrFarkoff]

Just check TDC on the Right side and there should be clearance on both valves but the inlet should be opening on the left preparing for the compression stroke the arrows should be horizontal both sides

Rotate the crank watching the inlet come to a close on the left and when at TDC again it should be the compression stroke and clearance on both left side valves and again the arrows should be horizontal both sides

 

[Bendy toy]

The chain length should not be a multiple of the sprocket sizes so it will precess as the engine runs. This will avoid the same links getting loaded every time and share out the loads/wear across the whole chain.

 

[monkeyboy]

The chain length should not be a multiple of the sprocket sizes so it will precess as the engine runs. This will avoid the same links getting loaded every time and share out the loads/wear across the whole chain.

That makes sense!

 

[richierex]

So how many teeth on the crank sprocket?

 

[Stewart H]

So how many teeth on the crank sprocket?

Eight and a half