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+--- Thread: Re-Sleeve block and large valves (/showthread.php?tid=717)
Re-Sleeve block and large valves - Robbie.watson@uk.bp.com - 20-01-2018
Hi all
In the process of building up a new engine for the special and think I need to sleeve the block. Can anyone recommend anyone that can do this at a reasonable cost? Thinking of putting the larger valves in too so any advice on suppliers that can cut the seats etc would be great!
RE: Re-Sleeve block and large valves - Stuart Giles - 20-01-2018
If the block is at +0.060" oversize, it might be worth seeing if the block will go to +0.080" over before going to the expense of sleeving.
Also, it's worth bearing in mind the sleeving process drastically reduces the strength of the block at the base; the top of the block parting company with the base isn't unknown where blocks have been sleeved on a performance motor -presuming that's where you're headed if you are looking to fit oversize valves.
RE: Re-Sleeve block and large valves - Alan - 20-01-2018
Unless you particularly want that block, a replacement, rebored, will probably work out cheaper than keeping the one you have.
Think carefully about larger valves. My opinion is you can hardly tell the difference until you hit 5000 revs.
RE: Re-Sleeve block and large valves - Bob Culver - 21-01-2018
I was interested in Alans comment that larger valves make little difference. Seven valves are not small and with the extra masking with larger valves I have always been sceptical of benefit.
If valves have old wide seats, or a lot of metal above or below the seating, a larger valve with new narrow seats will likely be better.
An article which possibly has prompted interest in larger valves is that on page 101 of Wyatts “The Austin Seven “. A new Cup Seven had a top speed of just 45 mph. A significant c.r. increase barely improved this, but 1/16 oversize valves increased to 55mph. The article is a bit of a mystery ; it is strange that car was originally so slow, and the exact cause of the improvement unclear.