What's it sound like?

My slant makes a soft, lower pitched knocking noise which begins as the engine returns to idle when warm. It starts at about 1100 and goes away at 7-800 (while idling). I don't hear the noise when the engine is loaded, or not decelerating.

It's not a rod, as there is no rod knock at higher speeds (gunning the engine and snapping throttle open and shut), and it doesn't seem to have the higher pitched click of the valve train or rocker snapping. Nor does it seem to make it on initial start.

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'81 W150 on Propane... Oversize valves, Oregon Camshaft cam, 10:5 static CR, Distributorless ignition, megajolt timing controller, PowerTrax lockers.

Piston slap tends to be loudest cold, and will lessen as engine temperature increases.

Small end bushing damage can act the way you describe, but I've only run into it once.

What is your hot oil pressure at idle?

2¢

CJ

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Part of Tyrde-Browne Racing

I don't know. The oil gauge reads half way and never changes. Idle or fast, the OP gauge always reads the same.

The noise isn't loud, it doesn't sound like piston slap to me and you can't hear it when running anything above a fast idle - 1100 or so. It is loudest just as the engine settles the last 150 rpm toward idle and then vanishes.

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'81 W150 on Propane... Oversize valves, Oregon Camshaft cam, 10:5 static CR, Distributorless ignition, megajolt timing controller, PowerTrax lockers.

I noticed this noise is louder as the engine gets hotter. It "could" be a rod knock, but I find it unlikely, as it seems a rod knock would have already resulted in blown out bearings and some serious banging by now.

I will, eventually, pull the pan and check the bearings. For now, though, it seems to be of little consequence. I am running 10-30 oil and was thinking of going to 15-40 industrial oil, just because it seems so darn thin.

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'81 W150 on Propane... Oversize valves, Oregon Camshaft cam, 10:5 static CR, Distributorless ignition, megajolt timing controller, PowerTrax lockers.

Pull your plug wires off one at a time with the engine running and see if the noise quitens or stops when you remove a certain one. That will at least narrow it down to which cylinder it is if its piston or bearing related.

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There's no such thing as too much cam....only not enough engine!