Cam Timing (once again!)

[vincereynard]

I am going to try using a pair of these, many because I have a set. -

http://qedmotorsport.co.uk/qed-shop/lot ... loy-centre

QED were particularly unhelpful with advice - " you get the crank and cams in the correct position and tighten the bolts." Thanks for that - most useful. Calling them "vernier" is also a bit of a cheat!

So anything I should look for? I have read that advancing the cams a couple of degrees benefits torque at the expense of the top end. "A 110 MOP becomes 108 ATDC for the intake and 112 BTDC for the exhaust."

I plan to rotate the cams to MOP position slacken the bolts then tweak the crank to the degree required then tighten. Can anyone see a problem with that? I am using the flywheel to turn the engine as it is out. So far my measuring (3 times) has shown a MOP of 109 degrees for the exhaust which was closer than I expected!

Then it is slot the engine in and off we go!

[john.p.clegg]

Vince

Be careful...don't drop the allens or cups down the front cover..

John

[Craven]

1st move, Make sure TDC is at TDC not just the mark on pulley.
Ron

[vincereynard]

Vince
Be careful...don't drop the allens or cups down the front cover..
John

That seems a distinct possibility!

1st move, Make sure TDC is at TDC not just the mark on pulley.
Ron

I've done that 3 times so it is as close as I can make it now. I've also adjusted the pulley mark to coincide. So if the disc slips I should get a hint!

[Chancer]

Calling them "vernier" is also a bit of a cheat!

That has long been a bugbear of mine!!!!

I have over the years come across a couple of sets that do justify the name, one had 10 dowel holes in one part and 9 in the other, a true vernier sprocket.

Another was like all the pretenders being sold today but did have vernier graduations etched on the hub and outer chainwheel.

[vincereynard]

Another was like all the pretenders being sold today but did have vernier graduations etched on the hub and outer chainwheel.

You would not have thought it was too much to ask for ?150! If I had known they were so "basic" I probably would not have bothered.

When they are set I shall probably etch a mark on both so that it is easy to see if they have slipped.

[Chancer]

On my X/flow race engines I just slotted the bolt holes, set the cam timing and then drilled through the sprocket into the cam and fitted a roll pin, then I removed the dowel and timed up a "wet race" retarded setting and drilled another hole 180? opposite, I made a removeable access plate on the timing chain cover, undo one bolt and swing it away on the other then remove dowel, release bolts to swing the timing to the other setting, replace roll pin in other hole, tighten bolts, refit access plate and away we go!

I never really got the point of (not) vernier pulleys, I think they just became a must have for later belt drive DOHC engines when they made them in snazzy anodised alloy colours. Of course then the boy racer has to run without the belt cover just waiting for a road chipping to give the drive belt the good news!!!

[vincereynard]

Bu**er it! Why should we be have to put up with second rate tosh.

They plainly are not "vernier" so its a misrepresentation of goods.

I've sent them back for a refund.

[Chancer]

Good on you!

Power to the people!

[oldchieft]

The real thing is found in this post: -

lotus-twincam-f39/cam-cogs-have-not-seen-before-t29618-15.html

Steve Curson, Vulcan Engineering,on 01474-874689 was the maker.

Jon the Chief

[promotor]

The real thing is found in this post: -

lotus-twincam-f39/cam-cogs-have-not-seen-before-t29618-15.html

Steve Curson, Vulcan Engineering,on 01474-874689 was the maker.

Jon the Chief

Hi Jon,

I'd be interested to know how adjustable these are as I can't get my head around them being as adjustable as the infinitely adjustable sprockets or "vernier pretenders"?

Cheers.

[Chancer]

Look at page 1 of that thread and you will see I gave an explanation there, then someone did a much better job and put it very succinctly.

Its always a surprise when I read one of my own postings without realising!

[promotor]

Look at page 1 of that thread and you will see I gave an explanation there, then someone did a much better job and put it very succinctly.

Its always a surprise when I read one of my own postings without realising!

I see now - in my haste I presumed that one vernier hole = one tooth and two holes = two teeth!

As you say the two descriptions were like chalk and cheese!

[vincereynard]

It looks like the inlet cam was timed way out which should come as no surprise!

It should be OK to advance the cams 2 degrees but I would like to check the piston / valve clearance first.

Does the old solder method still apply.

Currently it looks like I have Mops of inlet 112 and exhaust 106. Which is better than I expected!

[vincereynard]

I think all this ATDC and BTDC is too confusing and open to error.

To advance In. you decrease the MoP. To advance Ex. you increase the MoP.

Why not simply use the full 360 degrees?

Therefore ideal Inlet MoP is 110 and Exhaust MoP is 250. I am intending to advance 1 to allow for initial chain stretch so my ideal would be 109 and 249.

Measured In. averaged at 111 therefore I need to advance by 2 to bring it back to 109.
Measured Ex. 254 (106 BTDC) therefore I need to advance 5 to bring it back to 249.

Is this a huge mistake? It seems much easier to me!