Noisy F-head

All the f-heads I've ever been around were not quiet engines, but this one's got me worried about a rod bearing. Time to tear it down? I hate to. It runs too darn good.

 

Try to locate and isolate the noise(s) with a mechanics stethoscope - or a wood dowel to your ear. That will help you diagnose the exact cause more accurately.

Sometimes loose bearings can be improved with a new set of bearing shells, possibly undersized by a thou or two, with the engine in the vehicle.

Or go with a heavier grade of oil and run it until you can't.

 

X2 on pan pull

 

to check for loose bearings you can push the pistons down through the plug holes to see if they clunk

 

Typical bottom end failure would be a hammered rod bearing. Bang bang bang. That's what it sounds like to me. Since this engine has a forged steel crank, it is possible to replace the bearing shell and get some additional life from the engine, as long as it has not gone on too long.

So this is at idle, say 600 RPM, that's each cylinder firing every 2/10 second... sounds about right.

If you have a bearing that's so loose it clunks, oil should just pour out between the crank and bearing. I would expect very little if any oil pressure. I don't hold out much hope for that test.

If it's a specific cylinder that has a bad rod bearing, it should get much quieter when you pull the wire from that cylinder so it is not firing. That would narrow it down, but you'd still have to pull the pan and look under the caps.

 

I tried pulling one plug wire at a time. Didn't notice any reduction in noise. I need to try again with the engine hot. The oil pressure runs 30-35 at idle up to 60 at 2000 rpm and above.

I guess I'll be pulling it for repairs soon. I want to take the jeep on a long road trip this fall and there's some other drive train work I need to do. The T90 could use synchronizers and the t-case needs an intermediate shaft.

Hopefully the cylinders won't be out of spec so I can turn the crank, hone the cylinders and put it back together.

 

Pulled the pan and checked the clearances on the rod bearings. 1, 2 and 4 we're just over .003". Number 3 bearing shell was pretty beat up and the journal a little scored.

I polished the journal with crocus cloth and kerosene and replaced the bearing. The clearance is still over .005". It's not as noisy now, but I doubt it will last.

Planning on pulling it for repairs sometime next month. I have to get dad's flathead Ford finished and off the stand first.

 

There's an anecdote about shimming bearings like that in Andy Granatelli's book, "They Call Me Mr. 500." They Call Me Mister 500: Anthony Granatelli: 9780809296354: Amazon.com: Books - I read it a long time ago (in my 20s), and have lost my copy somewhere.

Howard's right, back in the day they'd build up the bearing with shim stock to get the clearance right. But this is way back, like the '40s and '50s or earlier. Doesn't wotk wth modern cast iron cranks, because the iron crank gets eaten away as much as the bearing. Forged steel only ... but all cars back then had steel cranks.

 

I thought about doing that. Still might.