Supersport cam timing

[Dave McCulloch]

I removed the verniers from my 1600 supersport last night (as they're going on the new engine) and replaced with the standard pulleys. Looking at the advance I had set on the verniers to achieve correct cam timing, the exhaust was advanced half a tooth (so I've refitted the standard pulley at the standard position) and the inlet was advanced about 3/4 of a tooth, so I've fitted the standard pulley 1 tooth advanced.

 

Then turned engine over gently by hand (plugs out) to make sure there was no piston to valve contact. Am I ok with the inlet advanced 1 tooth, or would I be better off setting it in the standard position and living with being out on the timing?

 

Thanks

 

Dave

[elise_s1]

Another thing I discovered (try it at your peril, though) is the slots for intake and exhaust are not aligned to the teeth in the same way. I mean if you use the intake slot on the exhaust and vice versa, you should end up with an advance/retard of 1/3 of a tooth. Not a refined solution, but definitively a cheap one! Obviously all the timing marks are useless on this configuration so not too nice to time it properly...

 

with both verniers (correctly timed) and pulleys out, you can align the vernier slot to the pulley slots to see which one give a closer tooth alignment and then copy the marks from the vernier to the pulley...

 

Cheers

Carlo

 

Edited by - elise_s1 on 1 Apr 2005 11:30:29

[Mike Bees]

No contact when turning over by hand doesn't mean no contact at proper rpm. An engine builder will measure the clearance during turning-over-by-hand to ensure it's not less than a certain amount (the recommended amounts escape me however).

 

Mike

[Tigger]

I had a 1.8K with 113 thou of lift without contact at TDC and that is somewhere close to 3mm (that is pretty close to the piston those and a mistake!!!.

 

Tig

[Sheds Moderator]

I think you have to measure it with a dial gauge before you make the decision. I think you'll be oK but for 20 minutes with a DTI I wouldn't risk it.

[Dave McCulloch]

The trouble is, to measure it with a DTI would surely need a complete strip down to use soft springs on the valves so I could measure the clearance to the piston at this position (unless I'm missing the point).

 

Mike - I agree, and hence my question as to whether anyone knew if one tooth out was still safe.

 

I think for the hassle involved, and the fact that it's only going to have this engine in it for about a month, I'll time it up per the timing marks - after all, I ran it like that for 6 years before fitting the verniers...

 

Thanks

 

Dave

[Mike Bees]

You don't need to fit soft springs, but you do need to have the head off and put some plasticine-like stuff on the pistons, bolt the head back on, turn it over a few times, take the head off, measure the thickness of the plasticine etc. Not exactly trivial.

 

Mike

[oilyhands]

Considering the valve acceleration with SS cams and the fact that in 8 out of 10 of the SS engine I have fitted verniers to the inlet pulley does indeed need to be advanced by one tooth I'd say you are pretty much certain to be OK. On a 1.6SS the engine will tolerate around 120 thou lift at TDC and still maintain sufficient piston/valve clearance. The cams lift at a rate of around 2.8 thou per degree of crank rotation, one tooth of the pulley is 15 degress so advancing the pulley will have added 42 thou of lift. Since most SS engines on standard pulley only have between 20 and 30 thou of lift at TDC you now probably have around 70 thou.. very safe. if you measure the lift at TDC in the conventional way (with a DTI head on, but cam cover removed) and it is 100thou or less then you are pretty safe.

 

Oily

[Dave McCulloch]

Thanks Oily

 

Checking my original measurements from before fitting the verniers, the lift at TDC was 16 thou, so I'm well within the 100 thou safe zone.

 

Cheers

 

Dave