KVW #88 Scratched for the Season
Discussion
After all the top end clattering from the n/s bank after Race 1 at the Rock on Saturday, the engines already been almost fully stripped. Unfortunately it’s not good news and I’m glad I did the sensible thing in not risking it on Sunday!
It appears that one of the top hat valve shims has disintegrated, damaged the top of a valve stem and . . . disappeared! The cam in question is not in too bad a shape; what we thought may have been a rounded off lobe (giving a vast clearance between the cam and follower) turned out to be the normal difference between exhaust and inlet profiles but that still needs checking out properly though. Re-profiling’s is an option if it comes to it as I understand the integrity of some of the replacement camshafts available is a worry. The leak down test done before the strip showed between 20% up to 56% losses on the bank in question although the other surprisingly ranged from 80% down to 24%! - it all points to inlet valve wear as there is clear evidence of significant burn between the valves on two of the cylinders in particular . . . so all the valves seats will need re-cutting too! Yet to test the valve spring compression rates (all double sprung) as we suspect this may be the root cause – valve bounce giving the shim the chance to move around, break up and escape is the latest theory! Unfortunately it gets worse - a re-bore will certainly be required as there is some scoring to most of the cylinders and distinctive lipping in two of them (about 2 thou after a quick measure) so consequently new pistons will be required. They too are all also scored to some extent around the skirt but there’s no discernible damage to the crowns at all. The scraper rings were noticeably worn and did not have the sharp edge definition of the compression rings. There’s some evidence of very minor damage to the cylinder head flat on one chamber as though something foreign had found its way in there but nothing too drastic. The oil scavenge pump gear doesn't turn as smoothly as the feed pump and there's some damage to the gear teeth so it'll be interesting to see what's found inside there when that's stripped! The big end bearings look OK – some wear but fine. The crank’s not out yet but the journals look OK too.
So all this would account for the loss of power towards the end of the race let alone lack of grip from my new slicks (whose temperature I never got right after the enforced well-shortened qually with a broken throttle cable)!
So, in short a total rebuild is in order which wasn’t budgeted for at all – so I think I'll be calling it a day for this year’s DTEC! We’ll be sourcing the various parts required a.s.a.p. so some of you may hear from us for info and/or advice! A big thanks to Rob and Dave at Boss Racing in Bexley who worked so quickly to get the engine out, strip it down . . . and who broke the bad news gently. I’ll be trusting them with the rebuild.
I’ll still be at Snett and Oulton though; to help, support and criticise where appropriate!
Looking forward to comments about cause and effect from some of the engine guru's out there too
It appears that one of the top hat valve shims has disintegrated, damaged the top of a valve stem and . . . disappeared! The cam in question is not in too bad a shape; what we thought may have been a rounded off lobe (giving a vast clearance between the cam and follower) turned out to be the normal difference between exhaust and inlet profiles but that still needs checking out properly though. Re-profiling’s is an option if it comes to it as I understand the integrity of some of the replacement camshafts available is a worry. The leak down test done before the strip showed between 20% up to 56% losses on the bank in question although the other surprisingly ranged from 80% down to 24%! - it all points to inlet valve wear as there is clear evidence of significant burn between the valves on two of the cylinders in particular . . . so all the valves seats will need re-cutting too! Yet to test the valve spring compression rates (all double sprung) as we suspect this may be the root cause – valve bounce giving the shim the chance to move around, break up and escape is the latest theory! Unfortunately it gets worse - a re-bore will certainly be required as there is some scoring to most of the cylinders and distinctive lipping in two of them (about 2 thou after a quick measure) so consequently new pistons will be required. They too are all also scored to some extent around the skirt but there’s no discernible damage to the crowns at all. The scraper rings were noticeably worn and did not have the sharp edge definition of the compression rings. There’s some evidence of very minor damage to the cylinder head flat on one chamber as though something foreign had found its way in there but nothing too drastic. The oil scavenge pump gear doesn't turn as smoothly as the feed pump and there's some damage to the gear teeth so it'll be interesting to see what's found inside there when that's stripped! The big end bearings look OK – some wear but fine. The crank’s not out yet but the journals look OK too.
So all this would account for the loss of power towards the end of the race let alone lack of grip from my new slicks (whose temperature I never got right after the enforced well-shortened qually with a broken throttle cable)!
So, in short a total rebuild is in order which wasn’t budgeted for at all – so I think I'll be calling it a day for this year’s DTEC! We’ll be sourcing the various parts required a.s.a.p. so some of you may hear from us for info and/or advice! A big thanks to Rob and Dave at Boss Racing in Bexley who worked so quickly to get the engine out, strip it down . . . and who broke the bad news gently. I’ll be trusting them with the rebuild.
I’ll still be at Snett and Oulton though; to help, support and criticise where appropriate!
Looking forward to comments about cause and effect from some of the engine guru's out there too
Edited by Keithyboy on Tuesday 21st August 16:51
Bugger I know how you feel chap, Currently waiting for the call myself.
Ive got one cylinder down on compression, but nothing obvious in the valley and cam, followers and push rods look ok.
dropped the sump, and thankfully nothing big fell out and pulled a couple of big ends, some wear but nothing major. the crank appears to be in one piece so far, and its still on std bearings so can be reground if needed.
there was a small amount of debris in the bottom of the sump, not much but certainly something that you wouldnt want to see.
Its almost as bad waiting for the news as getting it...
G
Ive got one cylinder down on compression, but nothing obvious in the valley and cam, followers and push rods look ok.
dropped the sump, and thankfully nothing big fell out and pulled a couple of big ends, some wear but nothing major. the crank appears to be in one piece so far, and its still on std bearings so can be reground if needed.
there was a small amount of debris in the bottom of the sump, not much but certainly something that you wouldnt want to see.
Its almost as bad waiting for the news as getting it...
G
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