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Just happened with Michael Harnesses’ car late last year. Michael tried the easy fix to roll-in new crank bearings and conn rod bearings. The easy fix dynoed at 152? torque/145hp?.
We all thought it would loosten up and the hp would come around. It didn’t and it re-knocked at RA this past weekend.
Chuck Taylor had 2 years of “roll-in/drive-on” luck.
Now we’ve got a new owner with a slight knock.
Can others share your experiences with the roll-in easy fix technique?
RP
[quote=“Patton” post=71259]Just happened with Michael Harnesses’ car late last year. Michael tried the easy fix to roll-in new crank bearings and conn rod bearings. The easy fix dynoed at 152? torque/145hp?.
We all thought it would loosten up and the hp would come around. It didn’t and it re-knocked at RA this past weekend.
Chuck Taylor had 2 years of “roll-in/drive-on” luck.
Now we’ve got a new owner with a slight knock.
Can others share your experiences with the roll-in easy fix technique?
RP[/quote]
Except in extreme cases where the engine simply wore out (likely several hundred thousand miles), bearing failure is just a symptom of some other problen in your engine. Off the top of my head, likely culprits could include a weak oil pump, out of round rod journals (big side), worn cam bearing journals (bad oil or excessive OCIs), or maybe just improperly sized rod or main bearings.
What were the rod and main bearing clearances during re-assembly? Did he inspect the oil pump clearances and gears? I’m also curious what kind of oil he uses and what his oil pressure was.
On another note, Afghanistan blows; I miss Stephanie, my dog, my cars, and my racing buddies (in that order).
I have never done the roll in method of replacing bearings, however, if the knock is coming back, i would suspect an oiling issue? Have you done any oil pressure logging?
The cases that I know of where this was attempted have been universally unsuccessful with time. Both on street and race cars. Some temporary relief is usually obtained, but long term success is dismal.
While you can mike the rod journals with the crank in the engine (so you can pick the correct bearings) you can’t do that for the mains. I have about zero faith in plastigauge for the precision needed, so actually measuring the journals is essential in my opinion. And if a bearing has failed, the crank needs to be polished.
But as noted other things could be going on. A worn pump, bad OPR, worn intermediate shaft or cam shaft bearings can result in lower than normal oil pressure and lead to bearing failure. Logging oil pressure (and looking at the data) goes a long way towards knowing what is going on.
I don’t know whether to be embarrassed or proud of the results we got in the old 401 motor. As far as I know, it had about 220,000 miles, with the last 10 years being primarily a track/race car. It developed a rod knock and when we dropped the pan and pulled the bearings, #6 rod bearings were shot.
Under the theory that whatever additional life I get from the motor is more than I was entitled to, we put in a set of standard rods and mains (and measured nothing…nothing, as part of the job). Might have put in a new oil pump while in there (can’t recall), but oil pressure both before and after the procedure was decent.
Motor was still running well if a little tired when I pulled it 18 months later. I know, YMMV!
Was it the same rod bearings that failed or a different rod?
I’m ok with the idea of spinning in new rod bearings, but the more measuring you do the less the liklihood of premature failure. Micing the crank journal and rod from underneath is entirely do-able. Borrow a mic calibrated in tenthou, or buy one on ebay. Practice a bit on some stuff until you’re getting consistent #'s, then go to it.
Plastigage isn’t worthless, it’s just not as good as real measuring. It would not be crazy to use plastigage and the old rod bolts when putting in the new rod bearings just to check and see if there are any surprises on bearing gaps before final assembly. If a person was unmotivated to really measure their bearing tolerances, with trivial effort, they could use Plastigage to ensure something wasn’t terribly wrong.
Certainly one has to be suspicious re. oiling when bearings fail. Sure, there’s few as obsessed with oil pan baffling and crankscraping as I am, but in the early days I lost several engines due to bearing failure, but I’ve never lost a bearings since I started using a properly baffled oil pan. IMO altho a crankscraper of some kind is useful, the best way to protect your bearings is a baffle on the right side of your oil pan and a door on the left side.
A huge bright oil pressure warning light at 20psi or so should indicate if your oil pump sucks air in a turn. Better yet is to log oil pressure. Usually folks have to lose a couple engines before their sufficiently motivated to log OP.
As Rich said, there’s a number of possible causes of low oil pressure. There’s a big difference tho between a person who has data on hot oil pressure at red line for a certain oil, and a person who only has a “general idea”. For example…lets say you have 50psi with VR1 20W50 hot at RL. Then you lose a rod bearing, replace them all and you still have 50psi. What does this tell you?
VR1 is a thick oil. A healthy engine should have better than 50psi hot at RL so something is wrong such that there is a gap that is allowing too much oil thru.
50psi should have been enough to keep your rods healthy, so the cause of the lost bearing probably wasn’t wear of cam lobes, head journals or oil pump. The cause might have been the oil pump pickup sucking air tho.
The fact that OP did not improve after replacing bearings might indicated that the gap problem creating reduced OP is in main bearings or head. Or even aux bearing or oil pump.
My point is that you if you don’t have a good feel for your engine’s behavior, it’s hard to draw conclusions about anything.