shaving head -How much is too much

[Redrum17]

We are rebuilding an A20A3 for oval track racing. We are using .30 over Venolia pistons. How much can the head be shaved before valve to piston clerance becomes a problem. We are running high octane fuel which should handle the extra compression. The cam we ran last year with a bone stock engine was a Delta 272. We plan to try a 282 next year with the high compression pistons, an aluminum flywheel and a three angle valve job next year. Any info on the head question or any other suggestions will be appreciated.

[gfrg88]

PM rjudgey. hes the man when it comes to knowing everything about headwork. hell even tell you what would be great on your setup man :rockon:

[88Accord-DX]

This is what Chilton says about warpage limits on the cylinder head.

If warpage is between .002 - .008 in ( .05 - 0.2 mm ) it can be resurfaced, anything in excess needs head replacement.

Anyhow, you can order a multilayer shim gasket to restore warpage in excess of the limits. (might be hard to find)

[Oldblueaccord]

We are rebuilding an A20A3 for oval track racing. We are using .30 over Venolia pistons. How much can the head be shaved before valve to piston clerance becomes a problem. We are running high octane fuel which should handle the extra compression. The cam we ran last year with a bone stock engine was a Delta 272. We plan to try a 282 next year with the high compression pistons, an aluminum flywheel and a three angle valve job next year. Any info on the head question or any other suggestions will be appreciated.


Clay it up and you tell us. its been discussed before here no answer that I remember.

Also as the head gets less it effects the timing belt remember and may effect the tensioner of it as well.

wp

[Kabuki]

If you look at the head, there are little reliefs cast in. They are set a small distance back (up if it was mounted) from the mating surface, and indicate the ABSOLUTE machining depth.

[2ndGenGuy]

I heard too, that shaving the head or block will retard the cam timing. So if you go too far, and don't have an adjustable cam gear to fix it, you may lose performance.

Sorry for not answering your question, just thought I'd throw that out there.

[Tomisimo]

As far i know thet for every 0,3mm you shave you need to ajust 1 degree on timing, so i reken no more then 1 mm.

[Ichiban]

You can do the math. For every mm of head removed it will affect your cam gear location by a certain amount, based on the amount the centerline of the cam and crank are moved in relation to each other. The larger your cam gear, the less the effect will be. On the A-series, shaving the head causes cam timing to be retarded. Using the diameter, calculate the degrees/mm of the cam gear itself, and then divide by the amount of head removed.

ie: C=(3.14)d
360/C= Deg/mm
Deg/mm*Change mm= Change Deg

Right? The formula works because the timing belt travels along the pulley as the cam centerline moves towards the crank centerline. There is no need to calculate the chordal distance.

As for the valve interference, you could use clay, but I would assemble the head and block, and measure the valves max height relative to deck height at max lift, both intake and exhaust, with a vernier height gauge. Failing that, you could use a machinists square or a pair of dividers. Then place a piston at TDC and measure downwards from the deck (remember to subtract head gasket crushed thickness). This should give you a rough idea if there will be interference. You can measure reference for lateral position using the edge of dowel locations so you are in the right spot, as the valves move at an angle to the head.

Hope this helps.

BTW check the math as I'm drunk.

Cheers!

[Ichiban]

...And as always, rotate the engine by hand after assembly to check for interference.

[88Accord-DX]

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