cam timing, am I ok being .01mm out of range?

[Jared at Pelican Parts]

Ok, So I've got the cam timing set on my 83 SC, the manual specifies a range of 1.1 to .09 for the valve overlap. I install my tensioner and suddenly my timing is now at .08mm at Z1.

I've heard that it can be slightly out and it isnt going to hurt anything. The simple fact is, it was a mother****er getting it to this point.

Am I ok to just bolt it all up and be on my way now, Or do I have to explicitly have it set at 1.0mm

I'm wondering what the usual range is for people who advance or retard the timing as well.

[dtw]

.01 variance is probably fine on a stock SC. One of the wrenches I know tells tall tales about the factory putting the 2.7, 3.0, and 3.2 motors together by just finding the right hole in the sprocket and torquing down the nut/bolt, skipping the fine adjustment. This alleged procedure is attributed to the relatively lazy and forgiving cams/state of tune of those motors.
The question for your motor is, to what height is the other cam set? If one's at .08mm while the other's at 1.1mm, you may want to try to bring them closer together.

[Jared at Pelican Parts]

I havent even gotten to the other one yet

So basically its not an issue?

[Jared at Pelican Parts]

Can a mod copy this thread over to the engine building forum as well?

[Early_S_Man]

Jared,

Your numbers don't jive! Typos of a multiple nature, perhaps???

Are you saying the spec is 0.9 mm to 1.10 mm, and that you are currently at a valve lift value of 0.80 mm, making the value off by 0.10 mm??? Are both sides at the identical 0.80 mm?

If I remember the discussion in BA's Handbook, there are three sets of specs used over the years in various 3.0 & 3.2 engines, and the set you are using is the 'low' set. If so, it [your current value] would be a value outside the factory range of values ... not a good thing! If I am incorrect, and the spec range you chose is, in fact, the 'middle' set, then you would be within factory specs, al all should be OK!

[dtw]

Having consistent timing between the two is the greater issue - if you can get 'em both within .01, you should be fine. I don't think .08 is a problem, but you might want to give some of the resident pro builders a call, like Henry Schmidt or John Walker.

Edit: Re-read your post and Warren's - agreed - if you are off by .01mm, that's one thing, but if you're off 0.1mm, I'd try it again until you get inside the 'window'.

Are you timing this thing in the car? I've done that and it is a pain. More respect to you if you are doing this for the first time - much easier to do a few times outside the car on a nice stand. Well done and hang in there!

[Jared at Pelican Parts]

Ok, the factory specifies a range between 1.1 and 0.9 (my mistake), in which case my overlap would currently be at 0.89

First time done, partial engine drop.

Thanks to John Walker as well, he's really been helpful, taking my calls and giving me advice

[john walker's workshop]

0.89 is pretty much 0.90. not a problem. most folks like to go for the upper range though. just a tad better low end performance.

[Jared at Pelican Parts]

SO I should also check the other side as well?

What tolerances should the two be within? Is there a specific range they should be within each other? like say .2mm?

[mb911]

I thought the spec was a little higher then that something like 1.60mm but last time it was my 81 sc engine anyhow thats what mine is at maybe mine is wrong who knows it sure runs good but maybe I should be resetting it

[MotoSook]

1.4-1.7 is the Euro spec....9-1.1 is the US spec. I'm with JW in that the upper end of the range is what I aim for.

I know it's a little tough with a partial drop Jared, but I'd aim for the upper end. I'd try to get them to within 0.05mm. I just timed a Euro 3.0 and both sides were at 1.625mm +/- .005, but that's with the engine on a stand.

[Jared at Pelican Parts]

Finished.

OK, the main thing I learned from this, is that the rebuild book does not specify how the tension of the timing chain affects the adjustment. I ended up constructing a turnbuckle that would allow me to set tension and then make an adjustment based on that tension.

The book shows a pair of vice grips holding the idler arm all the way to the top of the case. This was what was causing my out of spec reading. Working with the turbuckle, I was able to get the left cam within spec.

All good now. Thanks for everyone's help.

[MotoSook]

Good job Jared.

For the archives: mechanical tensioners are a great tool for cam timing. Cheap on E-bay..but hardly something you'd need to have in your tool box for routine meaintenance. I think Wayne has a picture of a mechanical tensioners in the book...

[dtw]

Originally posted by Jared Fenton
Finished.

OK, the main thing I learned from this, is that the rebuild book does not specify how the tension of the timing chain affects the adjustment. I ended up constructing a turnbuckle that would allow me to set tension and then make an adjustment based on that tension.

The book shows a pair of vice grips holding the idler arm all the way to the top of the case. This was what was causing my out of spec reading. Working with the turbuckle, I was able to get the left cam within spec.

All good now. Thanks for everyone's help.

I'm a little confused by this. The purpose of tightening the chains during timing is to eliminate misadjustment due to chain slop. Yes, the timing is dynamic when the engine is running and load is varying, but static timing should be set with variables like loose chains eliminated. It sounds like you've introduced slop as a means of adjusting timing - but this is giving false readings if I understand you, and the concept of cam timing, bother correctly.

[camgrinder]

FWIW, on the SC cams .2mm is about 1 degree. If your off .1mm its only 1/2 a degree.

I like to see SC cams go in at 1.4 to 1.7 mm. This setting advances the camshafts and add a little low speed torque.

[84toy]

Another FWIW, I always set my cams on any engine to the advanced side of tolerance. As the engine gets time on it, the chains will stretch and wear and timing will retard with time due to the wear.