15 replies to this topic

[coopertrooper2001]

Model:MPI
Year:2000
Description of problem (please be as in depth as possible): Is there any difference to the usual process of setting valve clearances where roller tip rockers are installed? I assume its just a case of inserting the feeler gauge inbetween the roller tip and the valve



Supercharged MPI with 1.5 roller tip rockers

[Wil_h]

It's the same process, but use the feelers side to side not forwards and backwards if that makes sense.

[Gr4h4m]

wil do you use a different size for the rollers from the book?

[Dan]

Roller rockers will make absolutely no difference to the amount the push rods and valve stems will expand when hot and that is what the valve clearance in really there to accomodate. People do change the valve clearnace for roller rockers but myself I can't understand why, the cam and type of valves and pushrods used should really govern the clearance.

[cambiker71]

Roller rockers will make absolutely no difference to the amount the push rods and valve stems will expand when hot and that is what the valve clearance in really there to accomodate. People do change the valve clearnace for roller rockers but myself I can't understand why, the cam and type of valves and pushrods used should really govern the clearance.

The gap is bigger as the extra leverage from the higher ratio rockers means that with the same movement of the pushrod the valve opens further, so the same amount of expansion at the pushrod end of each rocker will move the opposite(valve) end closer towards the valve so the gap has to be slightly bigger to accomodate the extra leverage and movement, or the valve clearance could close right up as everything heats up.

[Dan]

True enough but the question was about the rollers making a difference, not the ratio. You are right though of course.

[cambiker71]

True enough but the question was about the rollers making a difference, not the ratio. You are right though of course.

Maybe i should have read it better, i was just assuming roller rockers were higher ratio, if the ratio is the same, like you say, it would (should) be the same clearance.

[miniboo]

He says he has 1.5 roller rockers so surely extra allowance should be given for this?

[ethana]

Model:MPI
Year:2000
Description of problem (please be as in depth as possible): Is there any difference to the usual process of setting valve clearances where roller tip rockers are installed? I assume its just a case of inserting the feeler gauge inbetween the roller tip and the valve



Supercharged MPI with 1.5 roller tip rockers

its similar to the ordinary setup except you take the reading from side to side not in and out.. to be more precise... if you insert you feeler blade in from the 6 oclock position and push it forward as in most cases, the roller tip will roll and this rolling action will hinder you reading. Left to right 3 oclock to 9 oclock will give you a precise reading.
remember to allow for the rocker manufacturers recommendations regarding clearances as they do differ from the book (slightly bigger)

[coopertrooper2001]

The guy who built my engine says set them to 0.012 for road use or 0.014 for track/high revs.

Edited by coopertrooper2001, 22 August 2008 - 11:42 AM.

[Ethel]

12thou is the standard rocker clearance with 1.2 ratio rockers, 15thou would allow the same clearance on the cam side of the rocker with 1.5 rollers. I might be inclined to try a little more if it's a non standard cam. See what the cam manufacturer suggest and do the same divide by 1.2 times by 1.5.

[coopertrooper2001]

Did the clearances to 0.012 and there is a fairly sizeable rattle at low revs now making me think they are too loose? The rattle is like a couple of nuts banging about in the rocker cover.

I have rechecked the clearances and the tightness of the locking nuts. Not had this problem before - any advice?

[coopertrooper2001]

I am running a Swiftune SW5i Cam.

[Wil_h]

wil do you use a different size for the rollers from the book?

I use the value specified by the cam manufacturer.

I also have a tappet adjusting tool rather than use feelers, but use the feelers to double check.

Did the clearances to 0.012 and there is a fairly sizeable rattle at low revs now making me think they are too loose? The rattle is like a couple of nuts banging about in the rocker cover.

I have rechecked the clearances and the tightness of the locking nuts. Not had this problem before - any advice?

Rattles like this usually indicate worn rocker bearings in my experiance.

[coopertrooper2001]

Engine has done 6000 miles (inc the rockers) and I didnt have this problem before I fiddled with the valve clearances. I am thinking of doing them a bit looser and see what happens.

The car idles poorly now...