head shaving

fras · 01-21-2009, 11:34 PM

Can anyone tell me wht would be the limit for shaving head and block so as not to avoid problems with pistons or pressure,This is alumina 928 model 1979 4,5liter

928s · 01-22-2009, 01:11 AM

Is the purpose just to clean up the surface? Only a small shave should be required so no worries about the thickness, if you shave too much the water bridge can become an issue.

DPW928 · DPW928's Garage

The WSM has an area showing the limits and how to measure to determine if the head has been previously machined. IIRC the total machining cannot exceed 2.4mm and requires the installation of the thicker head gaskets or the engine will be subject to valve damage if the timing belt should break.

fras · 01-23-2009, 01:58 PM

Quote:

Originally Posted by DPW928

The WSM has an area showing the limits and how to measure to determine if the head has been previously machined. IIRC the total machining cannot exceed 2.4mm and requires the installation of the thicker head gaskets or the engine will be subject to valve damage if the timing belt should break.

I have to remove 0.5 mm of coroded top on each side, Head and block so 1mm will be Ok, Will i get anymore power while do this?

Danglerb · 01-23-2009, 04:02 PM

Do the pistons have that much clearance to the flat spots of the heads?

Nothing powerwise that you would notice, but combustion might require a higher grade of fuel, hard to say messing with the squish area.

DPW928 · DPW928's Garage

Just checked the WSM and page 15-19 indicates a .4mm limit so I stand corrected. i.e. the L shaped blocks on each side of the front and back of the heads should not be any thinner than 23.6 mm after machining. If less the 1.4 mm thick head gasket must be used.

Dennis

rich · rich's Garage

Quote:

Originally Posted by DPW928

Just checked the WSM and page 15-19 indicates a .4mm limit so I stand corrected. i.e. the L shaped blocks on each side of the front and back of the heads should not be any thinner than 23.6 mm after machining. If less the 1.4 mm thick head gasket must be used.

Dennis

My blocks are less than 23.mm as a result I had piston, valve, block and cylinder damage as a result of a broken cam. I used Cometic gaskets to pick up the clearance.