711M tall block (head) bolt holes

[miked]

Guys,

Re: above holes in block for head bolts. I am told that when the block is decked and these are extended that they often break into the water jacket. Can anybody advise as I also heard of grease being used as a seal. My limited knowledge of torque wrench use says that grease gives false readings. I normally clean the bolts, dip in engine oil, allow to drain and then torque up.

???

Mike

[elanman999]

Mike,
On my tall block engine I did not have to drill the holes any deeper but I did have to tap them (plug tap) down to the bottom of the existing hole. This gave enough thread length for the bolts.
Cheers
John

[promotor]

I ground off the bottom two or three threads of the head bolts when I did a tall block - tapping the existing bolt holes with a plug tap made me feel uneasy as there was a lot of resistance to the tap turning and I felt I was going to snap the tap in there which ends up being a "spark eroder" job to get the broken bits out. Or a scrap block.

Provided you have 1.5 x (d)iameter of the head bolt thread in engaged thread then you'll be OK - so if your head bolt thread is 10mm in diameter then 15mm of inserted/engaged thread is the minimum you need. I'm pretty sure Lotus head bolts are approx 25mm in thread length from stock. 1.5xd is the industry standard minimum for bolt thread insertion.

Oil on the threads is the way I dress my head bolts, with moly grease under the head of the bolt to let the head slide easily. I used to use moly on the threads as well (due to moly's sliding properties) and never had any issue whatsoever but now use oil simply because it's quicker and had read articles about grease not being so good for the job (the article didn't mention specific greases though). I think if you are to use grease on bolt head or thread it should only be moly grease due to its "platelets" which allow the "slide".

[rgh0]

The first question to ask is why deck the block in the first place? - people do it to use standard twin cam piston compression height pistons with standard 1600 tall block ford rods, which is fair enough, but it does weaken the block

If you want a long stroke motor I prefer the options of using a 1500 block with low compression height pistons or a 1600 block with special rods and / or pistons to get the piston height you want without decking the block.

cheers
Rohan

[miked]

Guys,

Thanks for the replies. I should have told the whole story.
I had a nice 711m block, crank, rods and a set of nice twin cam pistons. The guy who does our engine work and others said it would make a nice engine. I also have a nice QED 420 head, this is what started this idea off. The bottom end is now done. He even put it together for me after the initial dummy build to get the deck height right. As we lifted the short motor in the back of the car he told me that he had gone into the water jacket when opening out the head bolt holes. He is very experienced and has done lots of twin cam stuff over 30 odd years. I asked about sealing and he said to just apply grease.

Hence the question. Have I got a problems. Whilst I understand that water pressure is cap pressure am I OK with what I have got.

Mike