northiam

Help.
Only at 6500 revs and beyond the Clevo makes at cracking metallic kind of noise, whether you rev it under load or in neutral. What could it be? No damage is apparent but it scares the crap out of me! Can’t help thinking its piston to valve clashing. I’ve posed this question before, any ideas. I'm running crow springs 7333
1.820" installed height
125 # closed
290 # open @.500
Crow Solid Cam 21626 .560 in .570 ex ( F238)
Zero decked block, 302 6" rods, ACL hyper pistons, terra roller rockers.

Or could it be something else?

shaynet

Have you had it on a dyno? Maybe the A/F ratio is leaning out at those kind of revs. R U still running a mechanical pump cause they can't keep up at those revs.

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svo347

It wouldnt ping when its not underload tho if it was leaning out.
fan noise maybe?

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northiam

Surely a slightly lean condition would cause that noise? Still running mech fuel pump, and thermo fans. Is there a way of telling if valves are clashing without removing the heads? Right thru the rev range its ok until you hit 6500! Its got me f***ed.

ch7472

Pull the plugs out and have a look for metal if none there you no its not going lean. What comp is the engine and is the fuel you are uesing up to the task.

shaynet

Pull the plugs and have a look with a torch at the top of the pistons while turning it over by hand to see if the valves are hitting

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The cop said "Do you know why I pulled you over". I said " Well, that all depends on how long you have been following me!"

STROKEXD

northiam you are being too hard on your motor by free revving it to 6500, not a good idea.

Seriously suggest you seek professional advice from a dyno tuner ie run it up under load with full diagnostics see what's happening.

Mate if it keeps making the noise when you pass 6500 and beyond, then can I make a simple suggestion. Stop doing it. With those cam specs your motor peaks at 6000-6300 anyway so are we to call you big rev Kev or something?

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TruBlu351

Didn't we say it was most likely valve bounce?

I bet your engine takes a big drop in power as this is happening anyway, so just give yourself a ~6300 redline. Someone more edumacated than me can tell you if those spring pressures are good for 6500+

Don't hold your breath with the "no apparent damage"! As soon as that valve drops into the cylinder it'll be all over. Easy fella..........wooo boy

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4Vman

6500 is past best revs for an F 238, id say your expecting too much from the cam!

northiam

Its still pulling hard at 6500 and feels like theres a lot more in it! I agree if it was valve float the power would seroiusly taper off. The HO revved at 6500 with no issues.
Could the combination of zero decking and 302 rods dwelling longer @ TDC be causing clashing? Could I back the valve lash to 0.030+ to reduce lift and duration as a trial?

The F238 and F246 use the same springs and closed pressures same as the crow cams, so the guys using the F246 with a greater overlap period would be more likely to have this problem too! But you dont, why?