piston/valve clearance too tight, barely.

[slakjaw]

hello everyone

Well I got the cam timing done tonight then I moved on to the Piston to Valve clearance check and here is what i found.

intake 1.5
exhaust 1.5

very close but I was hoping for a little more clearance.
the valve adjuster stops right at 1.5 on the left and right sides.

its a 1971 2.2 with Solex cams and S pistons.

so where do i go from here?
Should I have the piston valve relief'scut?
it already has 2 cylinder base gaskets. should i go to 3?
I had the cam towers resurfaced and I wonder if that could have messed up the rocker arm ratio?

I am using the method in Wayne's rebuild book.
Please give me your comments
Thanks
Kyle
71` 911

[Neilk]

I know nothing about engine rebuilding, but I do remember reading somewhere that you shouldn't use more than one gasket. If you need more than one, get a thicker one instead.

[rcwaldo]

have you set your deck height? This will be a factor in valve to piston clearance.

Chris

[Early_S_Man]

Kyle,

1.5 mm = ~0.060" ... sounds OK to me

What were you expecting? I have never heard of any clearance problems with Solex cams and 'S' pistons! Not below 7300 rpm, anyway!

[Wayne 962]

You must have at least 2.0mm on the exhaust valve, or you will have problems when you run the engine (and it gets hot). This is a real problem.

You probably have a bunch of 'tolerance buildup' from a whole bunch of machining processes (case spigots, heads, case centerline). In general, the Solex cams are milder than the 'S' cams, so it makes me take pause at your measurements?

Double-check and then machine the tops of the pistons if you get repeatable measurements. Double-check your cam timing to make sure it's correct...

-Wayne

[slakjaw]

The deck height looked good at ~1.8mm avrage,

i will check the cam timing again, i set it at 4.4 would that be correct for my motor?

i am really hopeing that there is something i can do to get the .5mm on the exhaust side without a teardown.

Thanks
Kyle

[Tyson Schmidt]

Using the adjuster method isn't accurate enough. You can end up with the edge of the valve hitting the edge of the valve pocket, because the pocket is designed to clear when the piston is ever so slightly below TDC. (Thjat's where clearance is tightest.) Since the valves are at an angle in relation to the piston, this means that when the piston moves down in it's bore, the valve head will actually be aiming at the piston a little more laterally, and properly centering in the valve pocket. You may have a few more millimeters clearance than you think.

You really need to use clay or solder to get a proper idea of what the clearance is. My guess is that you will have a lot more than 1.5mm when you properly check the clearance.

[slakjaw]

ok i double checked everything, using the solder method I have 1.7 on the exaust 1.9 on the intake and it looks like i need to advance my cam some. seems closer to 4.0 than 4.4 to me. i will adjust the cam timing today, if this does not give me more clearance maybe someone here would be interested in my Solex cams for some E cams.

Thanks everyone
I will let you know how it turns out
Kyle

[slakjaw]

hi again

ok i dissambled and added 2 more gaskets for a total of 1.0 mm of base gasket, reset the cam timing to 4.2 and the new numbers are.

intake ~1.8
exaust ~1.9 (off by 0.1mm)

i feel this is close enough.
anyone here disagree?

thanks for everyones help

Kyle
71 `911

[Early_S_Man]

Kyle,

Assuming that your chains are new ... you are supposed to set the timing value to max value of 4.4 mm ... and normal wear/break-in of the chain link's pins and rollers will retard the timing back to the nominal value of 4.2 mm within a thousand miles or so. At the 4.4 mm timing setting, I bet you will see additional clearance!

You did a 'valve' job, right???

As the valve seats break-in [pound-in, so to speak] and the valves get 'friendly' with them ... the valves will seat a thousandth or two further away from the pistons, so I think you will be OK.

[Early_S_Man]

Any update?

[slakjaw]

hi

I have been too busy with customers cars and havent had the time to readjust them yet.

I didnt think of the chains stretching, yes they are new. and i did do a valve job.

anyways i will post again after i have had time to adjust them yet again.

Thanks again

Kyle