piston / valve clearance help

[wgirardot]

I am in the process of putting my stock '82 SC engine back together after headstud replacement. The only other thing done during this was a valve job, with .14 mm removed to clean up the mating surface on all 6 heads. All else is original: pistons, cylinders, .25mm base gaskets etc.

I have set camshaft timing to 1.56mm on both sides ( right in the middle where it is specified for a 930/16 motor ). Now I am checking valve to piston clearance on 1 and 4 and seem to have a problem on both sides intake clearance. Left side is .75mm of clearance and right side is .55mm. Both the exhaust exceed the required 2mm min clearance so that is good.

What can be done to increase intake clearance as Wayne's book call out 1.5mm minimum ? I am kind of stumped what could be going on with a bone stock, unmolested, motor where the only thing that was done was head fly-cut of a mere .14mm


Bill

[stownsen914]

With the same parts and no (other) machining, that is certainly odd. How confident are you that you've got the cam timing correctly set?

[wgirardot]

Pretty confident on cam timing. 1.56mm on 1 after turning 360 degrees ( both ccamshaft dot are down ). Then 1.56mm on 4 after turning an additional 360 degrees ( both camshaft dots pointing up ).

[Zuffenwerker]

It’s easy to get tricked here. You may have squished your ….whatever your using…. with the incorrect cam timing while your turning over your engine WHILE setting cam timing. When you first insert your cam sprocket pins you probably didn’t get the hole right the first time. When you turn the engine to check your initial timing setting you are in accurately squishing your clay, solder, etc.

Assemble 2 p’s and c’s on one side of the engine. Insert the clay only in the second cylinder. Use the first cylinder to set your cam timing. Once the cam timing is perfect install rockers on cylinder 2 to check clearance.

Not sure if this is your issue

[mikedsilva]

Originally Posted by wgirardot

I am in the process of putting my stock '82 SC engine back together after headstud replacement. The only other thing done during this was a valve job, with .14 mm removed to clean up the mating surface on all 6 heads. All else is original: pistons, cylinders, .25mm base gaskets etc.

I have set camshaft timing to 1.56mm on both sides ( right in the middle where it is specified for a 930/16 motor ). Now I am checking valve to piston clearance on 1 and 4 and seem to have a problem on both sides intake clearance. Left side is .75mm of clearance and right side is .55mm. Both the exhaust exceed the required 2mm min clearance so that is good.

What can be done to increase intake clearance as Wayne's book call out 1.5mm minimum ? I am kind of stumped what could be going on with a bone stock, unmolested, motor where the only thing that was done was head fly-cut of a mere .14mm


Bill

Which cam are you running? Also what was your deck height?

To increase your intake valve clearance you will need to RETARD your cam timing slightly. Try for 1.45mm (with 0.1mm valve lash) and then re-check your clearance.
You should get near sufficient intake clearance, but double check your exhaust clearance as this will reduce slightly when you retard the timing.

You can run less than 1.5mm clearance on the intake but the extra is a nice insurance. Maybe 1.25mm is enough. You'll find the piston is on its way down and away from the intake valve....

[wgirardot]

I am running stock cams for an ‘82 SC w/ 930/16 series motor. I didn’t check deck height as nothing was machined on case or cylinders. I used new .25mm base gaskets


I will try setting my timing to 1.4 and see what I get. Thank you for your input


Bill

[wgirardot]

Also, I am using my original ( non-Carrera ) tensioners to apply tension during this cam timing procedure. Is this providing sufficient tension ?

Bill

[mikedsilva]

Originally Posted by wgirardot

Also, I am using my original ( non-Carrera ) tensioners to apply tension during this cam timing procedure. Is this providing sufficient tension ?

Bill

I would imagine so. With the tensioners installed, you should not be able to wiggle the chain very much. Just make sure it feels even on both sides.

[wgirardot]

They are tight as they should be in an running motor ( I rebuilt them ). Just trying to gleem more information before I dive back in. Cams are secured by the big nut vs. bolt


Makes me wonder if my motor is a “mutt” because there is a lot of confusion over when they switched over to the bolt. . Wayne says one thing and Bentley another. Nonetheless the cams are correct, and serial # on motor corroborate an ‘82 SC w/ 930/16 motor

Bill

[mikedsilva]

Originally Posted by wgirardot

They are tight as they should be in an running motor ( I rebuilt them ). Just trying to gleem more information before I dive back in. Cams are secured by the big nut vs. bolt


Makes me wonder if my motor is a “mutt” because there is a lot of confusion over when they switched over to the bolt. . Wayne says one thing and Bentley another. Nonetheless the cams are correct, and serial # on motor corroborate an ‘82 SC w/ 930/16 motor

Bill

I've always assumed the Big Nut is a stock SC cam unless someone reground it to a diff profile (unlikely).
Let us know how the clearances work out when you change the timing a bit.

[stownsen914]

A couple quick-ish ways to tell if your cams are non-stock:
- most cam grinders put markings on the cams, often stamped on the ends. Hard to see in an assembled a fine though.
- measure the cam lift. Most non-stock grinds have more lift.

[wgirardot]

Regarding cam timing technique: As long as I see the value I desire at the end of the process, does it matter how I got there? Doing a lot of tweaking the cam and moving the crank back and forth, massaging it in until locked down w/ proper torque).

Bill

[boyt911sc]

Bill,

If your motor is an ‘82 SC, your camshafts should have the bolts and not the big 46-mm nuts. Are you using a mechanical tensioner when doing the cam timing? What are you using to keep the timing chain under constant tension? Both sides should have identical deck heights and should be confirmed before you check the valve to piston clearance.

Tony

[mikedsilva]

Originally Posted by wgirardot

Regarding cam timing technique: As long as I see the value I desire at the end of the process, does it matter how I got there? Doing a lot of tweaking the cam and moving the crank back and forth, massaging it in until locked down w/ proper torque).

Bill

This is fine. Just make sure you rotate crank a couple times and verify you are getting the same lift on the overlap stroke. Do for both sides.

[boyt911sc]

Originally Posted by wgirardot

Also, I am using my original ( non-Carrera ) tensioners to apply tension during this cam timing procedure. Is this providing sufficient tension ?

Bill

Bill,

This procedure is causing you trouble setting the correct cam timing. You need a mechanical devise to get consistent chain tension during cam timing. The hydraulic tensioner is removed and replaced with a mechanical tensioner. Try this method.

Tony

[stownsen914]

Appropriately placed C clamps on the idler arms can do the trick as well to remove the slack in the chains.

[wgirardot]

Thanks for the guidance. I will use mechanical tensioners for cam timing. Question: Could I have caused any piston or valve damage during my failed attempts at timing? The dots on the cams have always either pointed straight up ( for cylinder 4 overlap ) and straight down ( for cylinder #1 overlap )and valve lash has always been .1mm during timing, and all the way open during testing as I rotated the crank a multiple # of times.



Bill

[stownsen914]

If there is slack in the chains, the cams won't keep the timing with respect to the crankshaft as you turn over the engine, and the valve opening/closing events will deviate from the intended timing. This could explain the out of spec measurements you're getting.

As for possible damage, if you're just turning over by hand and you didn't force it to get the engine to turn over, you shouldn't have had any piston to valve contact.