Timing chain adjustment

[ivan.wood]

I post this on a previous topic but in case I don't get an answer here it is again.

Had the head off my 1965 Elan and was just checking the timing chain and when the camshaft marks line up perfectly as per the book the crankshaft is about 5 deg ATDC. I don't have time to get a new chain and replace it but would it be better to set it 5 deg BTDC?

Thanks

[rgh0]

With the crank at TDC the cams will be slightly out according to their timing marks by 2.5 degrees each. What the real timing error is needs a lot of work measuring the cams and pistons rather than relying on the timing marks which may not be accurate. For a road engine a couple of degrees on the cams will not really be noticed.

The discrepancy is probably not the chain but most likely due to head or block machining or crank sprocket wear or timing mark errors

You could fit vernier pulleys or offset dowels if you wanted to get the timing closer but probably not worth the effort. If you wanted to play with the timing by shifting the chain one tooth I would probably go with the cam timing events being later rather than earlier as this may give you marginally more torque at the cost of a little top end power.

cheers
Rohan

[2cams70]

You may have accidentally swapped the inlet and exhaust sprockets on reassembly. Sprockets are the same but markings are in slightly different positions. Don’t fiddle with how they line up unless you know exactly what you are doing - i.e properly measuring valve openings relative to crankshaft rotation. Second guessing = trouble.

[ivan.wood]

Thanks Rohan, I just want to get the car running so you think it is better to leave it as it is with the 5 deg ATDC which it currently is?

The cam sprockets are correct as I marked them when I rebuilt the engine unless they were wrong before I dismantled it.

Thanks