I am running a non-hemi 212 with a 14cc milled head and champion rockers. During the last two races, the valve lash has loosened up in the first few laps resulting in a loss of power. The lash was set as tight as .001 and by the end of a 10 lap race on a small backyard track, it was over .005 while cold. Any ideas on why this would loosen up? Thanks.
Valve Lash Loosening During Race
- Thread starter WamaJama
- Start date
I set it while it was cold, ran it, and checked it again after it had cooled down.
KartRacingLA
Member
Doesnt make much sense. You may want to pull the side cover and check the cam lobes and lifters
This was my thought after the first time it happened. Made sure that wasn't the case and it still does it.
Horsepower4Hire
Member
On an engine with cast iron head, you would be correct but Aluminum block/Aluminum head expand at a different rate than the steel pushrods and valves causing the lash to loosen as the engine gets up to temperature.
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KentuckyFriedFixes
Member
There's lots of reasons you could be gaining lash. If this is a new engine, I wouldn't be too concerned over .004 as it will likely stop gaining lash once the cam is broken in. If this turns out to be an ongoing issue you'll need to start looking at a few things.
Rocker hardware of course, and I know you've already checked that, but even the best rockers can fail or crack so look a good eyeballs-on inspection may be needed. (Cracks aren't nearly as noticeable as a completely broken rocker)
Camshaft or lifter wear, pushrod wear or bends can all cause a gain in lash. This is easy to check with a dial indicator to see if your cam lift is less than it's supposed to be.
Soft valves can wear at the tips and even the valve face. A good look at the valves and seats may reveal an issue.
I would argue that the most common reason to have an engine gaining lash aside from break in or an issue with the rocker hardware, would be the use of high PSI valve springs on a non-welded lobe camshaft.
I hope your issue is just from normal break in and it resolves itself.
Rocker hardware of course, and I know you've already checked that, but even the best rockers can fail or crack so look a good eyeballs-on inspection may be needed. (Cracks aren't nearly as noticeable as a completely broken rocker)
Camshaft or lifter wear, pushrod wear or bends can all cause a gain in lash. This is easy to check with a dial indicator to see if your cam lift is less than it's supposed to be.
Soft valves can wear at the tips and even the valve face. A good look at the valves and seats may reveal an issue.
I would argue that the most common reason to have an engine gaining lash aside from break in or an issue with the rocker hardware, would be the use of high PSI valve springs on a non-welded lobe camshaft.
I hope your issue is just from normal break in and it resolves itself.