11 replies to this topic

[Raggedroy]

Hi, I have had a broken cam chain tensioner, while I have the cover off I'm planning on fitting a new vernier duplex kit. Without removing the head, how is the best way to set No.1 piston to TDC. The only way I can see would be put my gauge through the spark plug hole at a slight angle. Is there a better way?

 

Cheers

 

[Minigman]

That’s exactly what I would do too.

[Spider]

If you are only using standard gears and not concerned with exact cam timing, but only as set by the factory, just line up the dots on the sprockets.

[whistler]

If you currently have single chain then to convert to duplex you need to remove the 2 bolts that go through the timing backplate into the end main bearing cap, countersink the holes and fit countersunk screws; otherwise the duplex gear will foul the bolt heads. You'll also need to modify the timing cover where the crankshaft seal fits to stop fouling there as well. No need for a tensioner.

[Spider]

Hi, I have had a broken cam chain tensioner, while I have the cover off I'm planning on fitting a new vernier duplex kit.

 

(bolding is mine)

OK, so sorry, now I read this again with my glasses on!! that changes things.

 

I don't know of an accurate way you'll be able to measure TDC with the head on. Usually, when building an engine up, some builders will accurately mark on the Flywheel or Harmonic Damper TDC.

If you have Flywheel markings. you can go off these, they will be close, but not spot on. Expect at least +/- 3 degree error here.

 

Trying to measure with a DTI via the spark plug hole will be quite inaccurate, the angle is way off, let alone what the DTI may contact inside.

[InnoCooperExport]

If you´re going through the trouble of changing the timing gear, what´s the extra effort to pull the head? I agree with Moke Spider that through the plug hole you won't get an accurate reading at all. 

 

And as Whistler says don't forget to countersink the engine plate and change those bolts for countersunk screws. I put a dab of locktite on them as you won't be able to fit a locktab either anymore either.  

[Ethel]

There's a very credible theory that cam timing isn't as important as we think:

 

The siamese ports behave differently so a single profile cam has to be compromised on at least the inner or outer cylinders, probably both. It's what scatter cams are about. I'd fashion a dog leg probe to try and reach the centre of the piston and keep the dial gauge upright - start after TDC and turn the crank to get to before TDC going the long way round.

[Spider]

There's a very credible theory that cam timing isn't as important as we think:

 

 

With half decent CR, I can notice a 2⁰ change from the driver's seat.

[mini13]

make a dead stop from an old plug.

[Raggedroy]

The engine was built in the 90’s by MED, it had a cast duplex set up with a tensioner. Cheers for the input, I have an idea now to make a canter leaver setup that pivots from outside of the cylinder with the end point resting in the centre of the piston. I can then place my guage vertical just outside of the spark plug hole. If that doesn’t work I will have to take the head off.

[mini13]

Seriously, get a plug. Smash the ceramic out of it, and put a nut and bolt through it, knock office sharp edges with a grinder and stick it in no 1. You can then wind the engine over by hand til the piston stops against the plug, and use it to set up the protractor. Just get the reading equal at each end if the stop.

[Spider]

This;-

 

Seriously, get a plug. Smash the ceramic out of it, and put a nut and bolt through it, knock office sharp edges with a grinder and stick it in no 1. You can then wind the engine over by hand til the piston stops against the plug, and use it to set up the protractor. Just get the reading equal at each end if the stop.

 

It's the most accurate way, even more accurate than a DTI. It's also (more or less) how I do them when building them up.

 

I did actually read of this a few months back, but had totally forgotten the dead stop from a spark plug method.

 

Nice one Mini13