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By RodgerF - 11 Years Ago
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Hey all!
It's been a while since I've been on here. Sidetracked, work, life gets in the way, etc., lol Anyway, finally got the '56 up and running but shortly after break in, the engine started knocking after it would warm up. On cold start, I get about 45lbs of oil pressure and all seems well. Quiet, smooth and runs well. As it reaches operating temps, the oil light will start to flicker at idle then stay on as it gets fully warm. After, say, 1500 rpm's the oil light will go out but will immediately come back on after I let off the gas. Oil pressure when the light is on is 0. I have a separate oil gauge and temp gauge installed, temps never go over 180 so it isn't running hot.
The engine is a rebuilt 292. It was built back in '05 and broken in then but never driven. Everything seemed fine with the break in at the time. Fast foward to now and the car is on the road and now the oil pressure problem. Last night I pulled the pan and the first four main caps. Engine has about 30 minutes break in time and maybe 50 miles on it. Bearings look scuffed but there are no marks on the crank, cylinder walls still have a nice cross hatch. I'm hoping I can get away with just putting new mains in. Looking for suggestions/advice.
Thanks!
Rodger
Can't seem to post a pic of the bearings. Says "can't find instance of the editor"??
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By RodgerF - 11 Years Ago
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I did get it to upload as a profile pic. Makes it hard to see thought! 
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By RodgerF - 11 Years Ago
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Here we go.
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By Ted - 11 Years Ago
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Looking at the wear pattern of the bearings in the picture, it appears to be too much clearance. I’ll suggest a micrometer check of the journals and bearings and verify what the actual clearance values are. There’s a chance that the bearings are simply the wrong undersize for the crankshaft journals.
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By RodgerF - 11 Years Ago
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Thanks Ted, I was kind of suspecting the same thing. The receipts for the engine work show the crank was polished not cut and the bearings were standard sized. Looks like some measuring is in order.
Rodger
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By NoShortcuts - 11 Years Ago
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Hmmmm... Consider using Plastigage (red 0.002-0.006) to do a quick check on the main bearing clearances before pulling EVERYTHING apart to use the micrometer... 
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By NoShortcuts - 11 Years Ago
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From what you've said, when the oil is cold you've got some pressure, Rodger. When the engine is up to operating temperature and the oil viscosity changes, the pressure is lost.
No argument that clearances someplace are likely the issue. Consider checking the clearances in your oil pump, too, even if it is 'NEW'... and check the oil pressure relief valve mechanism.
Let us know what you find as you work through this.
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By 2721955meteor - 11 Years Ago
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if you are checking clearance in the car,install cardboard in2 mains along side one to be checked snug them up and check others (you need the crank sucked upto get a acurate clearance)
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By NoShortcuts - 11 Years Ago
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Hmmmm... GooD point!
I've only used Plastigage for checking engine bearings when an engine has been bottom-side up, i.e. with the oil pan up.
Thanks for correcting my suggestion. 
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By RodgerF - 11 Years Ago
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Thanks for the suggestions. Using the red plastiguage I had a clearance of .0035 with new bearings. We rolled the new bearings in primed the engine and everything looked good. Initial startup with 20w-50 gave right at 60 psi but pressure started to drop as the temp came up. Put maybe 10 miles on the car and by the time we got back had around 5 psi at idle and an audible knock from the crank just like before.
Is that too much clearance? Should I have went with the .001 or .002 oversized bearing? Anything else that can cause a drop in pressure like the cam bearings or something? Maybe I can talk Mr. Mummert into selling me one of his engines!
Thanks again,
Rodger
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By Hoosier Hurricane - 11 Years Ago
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.0035 is too much clearance. .002 undersize bearings would be in order if you can find them. Did you check rod bearing clearances also. They may have been polished too much also.
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By NoShortcuts - 11 Years Ago
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You've GOT to be frustrated, Rodger. While .0035 is 'big', you should have more oil pressure than what you're reporting.
Did you have an opportunity to check the clearances and by-pass pressure relief mechanism in the oil pump? No problem with the oil pick-up tube fitting up and seating in the oil pump... no distortion of the tubing where the neoprene seal fits that goes into the pump housing? IF the oil pump checked out okay, my thought would be to pressure feed the oil system to do a leak down test with the oil pan off. As you've said, you're losing pressure somewhere... IF it's not at the main bearings, it would seem logical to suspect a rod bearing or cam bearing... Oil flow to the rockerarms is restricted by design... Oil flow from the rod bearings is restricted by the squirt holes in the rods that face the camshaft... I'm drawing a blank on anything else that is pressure fed where clearance would be an issue...
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By RodgerF - 11 Years Ago
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I didn't check the oil pump but I've tried 2 new ones, both with the same results. Tee Bird Products show bearings in .001 and .002 oversize so I may try that next. I didn't check the rods but should have. When I pulled a main and saw the scuffing, I figured I had it solved. Next time I will pull a rod cap too, just to see what they look like. I really don't want to pull the engine again so I hope I can get it fixed.
All part of playing around with old cars I guess. On the other hand, I bought a new GMC truck that seems to run just about as well! 
Thanks again,
Rodger
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By 2721955meteor - 11 Years Ago
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the dyno man has a set of.002mains,unless he has used them.
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By NoShortcuts - 11 Years Ago
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Hoosier Hurricane (8/15/2014)
.002 undersize bearings would be in order if you can find them. Did you check rod bearing clearances also. They may have been polished too much also.
Rodger, per John's suggestion for main bearings...
eBay listing of .002 undersize main bearings Perfect Circle manufacturer, made in U.S.A. 2 sets presently available search eBay for item number 331039558951 Buy-It Now price - $79.95 says free shipping, but check the particulars on this...
eBay seller seems to have a good transaction record score... |