Heavy duty/adjustable push rod holes

Paul V8 · Post by **Paul V8** » Mon Dec 17, 2007 3:07 pm

Hello, can someone tell me what size the holes in the head have to be drilled out to to allow the larger push rods to be fitted. Thanks.

HairbearTE · Post by **HairbearTE** » Mon Dec 17, 2007 6:02 pm

I think it was Adam on here who had an issue with this and iirc he eventually went to 13mm. I think 11mm is technically enough IF all your castings and machining from the factory is spot on. I have a feeling this was covered in depth on a thread in the old forum so well worth a look before drilling anything!

stevieturbo · Post by **stevieturbo** » Tue Dec 18, 2007 6:40 pm

The problem is.....that more material needs removed from the head side...as opposed to the open side where the drill bit will naturally tend to wander.

The hole doesnt need to be big....its just a pain to get it drilled in the right spot.

CastleMGBV8 · Post by **CastleMGBV8** » Sat Dec 22, 2007 2:14 am

Probably easier to file the port side of the hole with a rat tail file, how much clearance is required? I think I will have to resort to adjustable push rods as I'm sure my preload is far too high.

I also have a pair of Buick 300 alloy heads, not sure you can increase the push rod holes on these as the ports are larger and there may be a risk of eating into the inlet port wall too much, anyone have any experience with these?

Kevin.