pinogg

Hi I am wondering if someone could help me out. I had a little dig I had accidently made in the top of the head and called the machinist to fix it and he told me he had to grind it a little about 6 -7 thousands so he recommended I do all the heads so I did. When I picked up my heads he had grinded off the tabs that align the head to the cylinder. Can anyone give me some advice on what I should do. My questions are?:
1). Can I put the heads on without the tabs
2). Can the heads be re-machined to put the tabs back and is that advisable
3). Did anyone ever run into this problem
Help!!!!!!!!!!!!!
Thanks Joe

RollingArt

Are you talking about the dowels?

If so, you just need to put new dowels in the holes and you're good to go. The dowels slip in and out. Don't assemble without them.

geolab

I would go in order:

1-yes, there is no problem at all, do not worry.
2- no
3- I don't know

personally if the tabs are missing, I would proceed with more checking and re-checking.
What I mean is that with the tabs, you would assemble on an engine carrier with cylinders at 45* whilst mounting.
Maybe without the tabs, I would rather assemble with a vertical 90* cylinders facing up, making sure all is centered, but the studs will center all anyway, and that's just me being me.
You will tighten the cam carriers to the heads first, there is zero risk.
Courage and regards, bring up the pictures

pinogg

Hey first of all thanks for responding but what dowels are you refering too. Is there dowels you can use to join your heads to the cylinder thanks joe

pinogg

Geolab thanks for responding but I heard that with the tabs stopping the movement of the heads they are likely to move , maybe I'm wrong but there's got to be a way to fix this thanks joe

geolab

Forgive them Joe, for they do not know what they are saying!!!
All my best, george

Steve Weiner-Rennsport Systems

Hi Joe,

I would never assemble cam housings onto head that didn't have those dowel pins that both locate & ensure a precise alignment between the heads and cam housings.

If your machinist removed them, I would either ask them to install new dowels that were appropriately shortened the same amount as what was machined off the heads, or secure another set of heads that are undamaged.

One cannot rely on the studs and nuts to maintain alignment and prevent oil leaks, given the forces acting on the cams, rockers, and valve springs.

NineMeister

A picture tells a 1000 words.

These are the tabs that I think were cut off the OP's cylinder heads:

NineMeister

As a result, the cylinders will not be aligned correctly with the cylinder heads on assembly.

In my view the only rectification would be to machine the head and cylinder to incorporate two diametrically opposed, hollow dowels in each cylinder head to cylinder joint. The dowels will need to be around 12.0 to 12.5mm diameter (maybe 0.500"), 10.5mm hole through centre, ~20mm (0.75") long, located in a 10mm deep counterdrilled hole in both the head and cylinder.

.... or you can just buy another set of cylinder heads.

geolab

I have measured the distance between the head tabs shown in the above picture and the mating tabs on the cylinders (below picture), on a factory mounted 993 engine. There is a space of 1mm sometimes be it on the horizontal tab face or vertical. On the engine I have, these tabs do no mate or touch, probably due to different heat temps of cylinder and head. Or was it someone shaved a bit, I do not know.
I thought cylinder alignment is more done on the mating between cylinder base and case, and it is not these tabs that align. Like on some old 911 engines that do not have these tabs at all. I am sure I am wrong.
Picture courtesy of Pcarworkshop

berni29

Hi

Your machinist wants to have a look at his insurance policy I think. Really you should be getting a new, or nearly new set of heads.

Berni