cam timing and verniers

Mr Quoter-vator Joined: 16 Feb 2004 Posts: 7405

just thought i'd stick this here as prolly interest a few. whilst reading chamdayaydaydthingy 's article on how his car is back together and wantin to play with the verniers....

chris, u said...just fiddle with the verniers a bit at a time until it feels strongest.

that sounds incredibly balljoicy......and would u really be able to notice the diff? imagine its like focusing a lens where u go thru the optimal point and have to go back to set it...wud u really be able to feel that strongest point and know that u'd then gone past it to go back a bit??

and is the optimal position for the cam timing likely to be where the cam manufacturer specifies? i.e. from the timing figures eg 17/57 57/17 (made up!) if u set the cams up using a degree wheel and dial indicator so that the inlet opens at exactly at 17 as specified, is this best?

OR are the manufacturers numbers more of a guideline and do u usually fin that optimum setting could be somewhere slightly different...??

cheers

JB

(sure that could have been asked a lot simply lol)

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

The manufacturers have a major problem with their engines.

They have to be reliable, not to stressed and have to be able to be driven over a wide power range.

Some granny may buy the car and not take it over 3krpm ever, whilst some boy racer will never let it drop below 3krpm.

So they have to make a comprimise, that comprimise is tame cam timing and cam profiles.

Re-timing the stock cams will change the power output and curve. Decreasing the overlap will help build up the lower end, you may gain 10bhp up to 4krpm but you may knock 15bhp off the top end.

And vice versa.

Mark stated that his used to be crap at the bottom end, but took off (his words) at the higher rpm's. He says it was set to 8, I set it around 5/6 and told him to drive it and see what happens.

You do notice the difference. However getting the optimium is nigh on impossible without a spell onth e rollers.

Mr Quoter-vator Joined: 16 Feb 2004 Posts: 7405

is this also the case with aftermarket regrinds or something? would settin it to their figures also be a compromise?

i guess timing it to true figures is a good place to start...

so if one has regrinds (like moi) lets say in and out were both set spot on to manufacturers timing figures..which is the way to play it for increased top end, increased btm end etc etc...?

cheers

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

to an extent yes, no 2 engines are the same they will each require very different fueling needs etc for the same power output.

Increase in top end advance the inlet, retard the exhaust.

Vice versa, you can also alter where the valves open on the engines stroke but then it gets fiddly.

Mr Quoter-vator Joined: 16 Feb 2004 Posts: 7405

does anyone sell cheap verniers....when i say cheap i just mean normal...not fancy anodised ones that cost a fuckful!?!

Forum Moderator Joined: 16 Feb 2004 Posts: 1356

They all come like that afaik

Mr Quoter-vator Joined: 16 Feb 2004 Posts: 7405

tut....bloody hell...bet they only cost a fievr to make and all...

Gay Rights Activist Joined: 07 Apr 2004 Posts: 1268

if ur feeling brave, just take the location pin out and time them that way. its a popular misconception tha the pin drives the cam, it doesnt, it provides a location to keep timing "correct". its the force of the bolt holding the pulley on2 the cam, and provided u torque them up correctly they will be fine

Mr Quoter-vator Joined: 16 Feb 2004 Posts: 7405

oooo now u would have to be brave to do that...although thats an interesting idea...but even tho im sure without the key, torqued up enough it wud be fine id still be paranoid...
difficult to turn the cam shaft a little bit tho??when timing?

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

The keyway allows a degree or so of adjusment if you rock it back on forth on some, its not that tight a fit.

And the bolts tightness like Stan said is what keeps the timing.

And with that set up it is hard to set the timing.

Mr Quoter-vator Joined: 16 Feb 2004 Posts: 7405

i imagine it is very difficult....quite often the cams r half on/off and whenever slack is opened they jump to the next relaxed position....

Gay Rights Activist Joined: 07 Apr 2004 Posts: 1268

this is true, but im gonna try it before forking out 4 vernier pulleys.
plan is to somehow lock the inlet cam at max lift on whichever cyl, then time crank so it is about 100deg ATDC on the ind stroke of the same cyl

Mr Quoter-vator Joined: 16 Feb 2004 Posts: 7405

good effort...maybe some sort of arrangement like mole grips/clamp on the shaft of the cams when in the max lift position. only trouble i cud see maybe the difficulty of holding it tight enough to allow you to put sufficient torwue on the bolt to undo it and do it back up without it slippin.....i.d be intereted to see this one as i would have a dabble as well...as u said, would save a fortune on verniers...

Level 5 User Joined: 18 Jun 2004 Posts: 114

I have my own timing specs for the hy draulic profile which i find work best.

i.e. nick Hill retards his inlets to stabalise the idle...i do not, so it'll idle lumpy and sometimes be horrible when the days are cold...but with the SMT6 we can control idle quite well, and it actually likes it quite lean the F7P's.

plus, i HATE timing with the traditional max lift at 'x' degrees......leave a fair few degrees of dwell and inacurate timing. And you cant time a cam using the IO/IC/EO/EC.

Using std pullies is ok, but its a tad harder to knock the cam back and forwards by 0.01mm lift at a time that way.

Besides, pullies are only about 120.

Mr Quoter-vator Joined: 16 Feb 2004 Posts: 7405

so if u dont time at X degrees how do u time?

Forum Moderator Joined: 18 Feb 2004 Posts: 7432

dont you use that x degree at 1mm valve lift method? or am i thinking of something else?

Level 5 User Joined: 18 Jun 2004 Posts: 114

I use lift on overlap because its easier, you can do it with the engine inplace, and the cam is on the ramp/flank so there is only 1 point where the correct lift occurs, unlike peak lift which has quite alot of degrees dwell.

Gay Rights Activist Joined: 07 Apr 2004 Posts: 1268

i know its a better method, ok....but if ur not given a figure of lift @ TDC, how can it be obtained or is it a case of finding the sweet spot

Mr Quoter-vator Joined: 16 Feb 2004 Posts: 7405

cant u find the centre of dwell? ..rotate too and fro to a certain lift...divide the angle the crank has moved between two lifts in half to find centre.

Level 5 User Joined: 18 Jun 2004 Posts: 114

Thats still a bit laymands and crude., it'll never be spot on.

Stan....ALL cam manufacturers will give you the info.

Mr Quoter-vator Joined: 16 Feb 2004 Posts: 7405

so u move the crank to x degrees where overlap ends/begins and then set the lift to correspond?