I just got back from the Portland historics. Things were great until a rod froze and came out the side of the pan. This is a wet sump system and i am having a learning curve problem. One of the local experts that also runs a small block Chevy said i should switch from the large diameter rod journal diameter crank to the small one. his point was that since oil supply was critcal the small journal used less oil and placed less demands on the oil supply. any of you experts have an opinion on this?
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Re: Rod journal size re oil requirements
Jerry;
We just went down this road about a week or two ago. I would wait for the experts to chime in. We talked about "shear" and a bunch of other factors, including how/why the late 50's early 60's Pontiacs couldn't keep their bottom ends together due to too large of crank journals. In NASCAR they cut them down and used undersize bearings in order to keep them together. You'll hear a lot more from others I'm sure.
Stu fox -
Re: Rod journal size re oil requirements
It would help if you would post a photo of the rod when you get it out, but I will tell you that most broken rods I've looked at exhibit a bending mode failure, and the likely cause of such a failure is the rod bearing seizing due to oil starvation. When the bearing seizes the rod experiences a HUGE bending load and snaps like a tooth pick.
The oil starvation is most likely due to the pickup being uncovered or air entrainment in the oil, not some minor difference in journal size or oil viscosity. Brief periods of starvation due to an oil/air emulsion at the pickup may not be detectable on even the most responsive oil pressure gage (and you can't look at it continuously while your driving on the track, anyway). Such damage may be only minor per episode, but cumulative - ultimately resulting in sudden seizure.
That's why SCCA finally let production classes go to dry sump systems in the late sixties or early seventies - can't remember the exact year.
Once dynamic loads get up to about 1g, keeping the oil around the pickup is problematic, both due to "slosh" and that fact that there is two to four quarts of oil up in the engine that can't get back down to the pan due to crankcase windage and what does usually has a lot of entrained air.
Sorry to hear about your misfortune, but the fact remains that even current "vintage" classes that try to maintain some semblence of "vintage" performance via tire and engine configuration restrictions still results in more grip and higher revs than 40 plus years ago, so vintage racing organizations have the same dilemma as SCCA did back then - keep the cars "stock" and let them blow up regularly costing racers a huge amount of money and grief or allow dry sumps so the engines can live.
DukeComment
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Re: Rod journal size re oil requirements
Ouch! Premature ventilation of an engine is never good.
I think the local expert is right, but for the wrong reason.One of the local experts that also runs a small block Chevy said i should switch from the large diameter rod journal diameter crank to the small one. his point was that since oil supply was critcal the small journal used less oil and placed less demands on the oil supply. any of you experts have an opinion on this?
Switching to a small rod journal, if accompanied by a corresponding reduction in the size of the big end of the rod, will yield less rotating mass and the engine will spin up quicker..... definitely a good thing.
As to the oiling issues.... I dunno. Not an oiling expert. However, I've run large rod journals in my racing engines for 9 years with no oiling issues.
Next engine, though, is going to have small rod journals (283, or maybe even Honda) just for the reduction in rotating mass.
JimComment
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Re: Rod journal size re oil requirements
I don't believe the trend within NASCAR to run 283 mains and Honda rods is a restrictor plate phenomenon. Check EPay shortly after any NASCAR race and you'll find tiny journal cranks with bizarre strokes.
"Only driven on Sunday's". Eyeeeeah, right.
JimComment
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Re: Rod journal size re oil requirements
i am not sure that that setup will stand up to 9800 RPMs and 850 HP. they do use it in the truck and busch engines because they are limited by carb size to the HP and RPM they can turn. if there are no rules against it a lot of short track race engines use this set up to get quicker acceleration off of the corners.Comment
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Re: Rod journal size re oil requirements
Jerry, I have bought road race pans from Milodon that had trap doors (4 I believe) that kept the oil from going to the corners of the pan. At one time someone made a swinging oil pump pickup. This is going back further than my memory will work.Dick WhittingtonComment
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Re: Rod journal size re oil requirements
Why not? The cranks and rods don't have to survive that abuse for 100000 miles. 500 (or maybe 501) miles and they are done; that's fewer than 500000 revolutions. Afterward, the rotating assemblies don't get re-used, they get sold (to unsuspecting buyers).
JimComment
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Re: Rod journal size re oil requirements
'Used to run a large journal small block with a Canton road race pan with no problems. 'Used a warning light (big and red) in addition to the gauge so could monitor the P' a little easier through the twisties. 'Later switched to small and seemed to notice quicker winding and still no breaking problems.Comment
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