Joined: Aug 2017 Posts: 15 Threads: 5
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Location: Buckingham UK
Hello all, I am about to assemble my engine for a road car, the first one in a long time and I have a few questions. The engine will have a Paul Bonewell fast road cam, mildly lightenened flywheel, oversize inlet valves ( because the block was on the shelf complete with valves all unworn), 1 1/8 SU carb and Honda pistons. I believe the pistons are 50 thou low on the block which I intend to fix to the crankcase with a neoprene gasket. My questions are
1. How high is a standard block?
2. Should I reduce the block height so the pistons reach to the top?
3. Do I reduce the height at the top, the bottom or some of each?
4. Do I increase the reduction for the gasket thickness.?
I have had several differing answers to these questions and would like to find a concensus.
Colin
Joined: Aug 2017 Posts: 315 Threads: 1
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Location: Bristol
Why use Honda pistons when sports piston are available it only complicates assembly as Honda pistons have 13mm pins so you need to bore out the con rod small ends.
Terry.
Joined: Aug 2017 Posts: 1,257 Threads: 32
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Location: Cheshire
Car type: Race Ulster, 1926 Special, 1927 Chummy, 1930 Box
Agree with Terry. We all used Honda pistons a few years back when there was little else. The slipper pistons available from at least 3 of our suppliers are excellent for both race and road engines, and you don’t have to modify anything. Actually they work out cheaper, too.
However, to answer at least some of your questions:
You do need to set the piston height, but the best way is to loosely assemble and measure how much metal has to be removed to get the deck height correct. Take the metal off the top face- the bottom flange is weak enough already.
Alan Fairless
Joined: Aug 2017 Posts: 3,215 Threads: 100
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Location: Darkest Bedfordshire
No way on earth would I machine 50 thou off a decent block if there was another way of doing it.
There are plenty of good pistons around, sports or otherwise, and in the old days we used to cheerfully re-use good second hand ones with new rings on.
If you are hell-bent on using the Honda pistons I'd use silicone sealant instead of a base gasket and assemble while soft, effectively you get a metal to metal joint, so no added height.
Joined: Aug 2017 Posts: 15 Threads: 5
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Location: Buckingham UK
OK but the pistons are new and I have had them for several years. I agree with using sports pistons so does anyone want a set of +40 thou Honda pistons and a set of crack tested and mettaled rods bored for Honda pistons?
Joined: Aug 2017 Posts: 1,397 Threads: 25
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Location: North Yorkshire
19-08-2018, 12:41 PM
(This post was last modified: 19-08-2018, 12:55 PM by Steve Jones.)
Honda piston sit 1mm ie 40 thou below the top of the block. In the days we used them the norm was 10thou of the top of the block, 10thou off the bottom, 10thou off the top of the crankcase and don't worry about the last 10thou!! My trials engine's like that and has been for 10 years. It goes well!! However, nowadays I agree that the sports slipper piston are the way to go and that's what I've used on more recent engines and as well as being excellent, they save a lot of messing about.
Steve
