8 replies to this topic

[Timrobins]

 image0.jpeg   180.28K   9 downloadsHi, my son is rebuilding a 1275 A+ 

He is currently fitting new timing chain and sprockets, but with number 1 piston at TDC the two marks on the gears will not align.

I think the mark and corresponding tooth on the crank sprocket should point directly at the centre of the end of the cam shaft, but it doesn’t?

any suggestions?

 

Many thanks

 

 

Edited by Timrobins, 22 January 2024 - 04:08 PM.

[KTS]

fit it as best you can, then measure the cam timing to establish what the actual timing is.  then you may be able to adjust using offset keys

 

https://www.minispar...odruff key.aspx

[weef]

It is difficult to tell from the angle of your picture but it looks as if the crankshaft is not at  TDC from what I can see from the crankshaft keyway possition.

I may be wrong as I say but it is worth ghecking.

[Timrobins]

It is difficult to tell from the angle of your picture but it looks as if the crankshaft is not at  TDC from what I can see from the crankshaft keyway possition.

I may be wrong as I say but it is worth ghecking.

Hi, we have double checked TDC several times, but the crank sprocket does not seem to line up properly.

[KTS]

i wouldn't assume the markings (..or the keyways for that matter..) on the sprockets are particularly accurate - i'd treat them as more a guide to initial assembly and take it from there

[Lplus]

Just make sure that both dots are on the line between the centre of the crankshaft and the centre of the camshaft.

[weef]

If you have them fit the old sprockets one at a time to try and determine where the error lies.

[nicklouse]

Forget the dots and measure. 
 

there have been some timing gears that should not have passed quality control.

[Cooperman]

Forget the dots and measure. 
 

there have been some timing gears that should not have passed quality control.

 

That's absolutely right, Nick.

Original as built sprockets were more-or-less accurate enough for normal driving, but all components have a manufacturing tolerance. After-market sprockets and cams can be well out of tolerance when compared to originals.

You need to get a crankshaft protractor and a DTI and actually the as-installed cam position, then use offset woodruff keys to correct the error. I always set to 2 degrees advanced from nominal when fitting a new chain and/or sprockets to allow for initial chain stretch. Thus with a cam which should be timed at 110 degrees ATDC on the inlet, I set to 108 degrees ATDC.