I'm presuming that you've replaced the oil cooler and lines after each
blow-up. That's one part of racing I really and truly hate - throwing out a
perfectly good, virtually brand new oil cooler because you never really can
get all the crap out of it...
I presume you have a wet-sump, hence the Accusump. Here are the things I
would think about.
1. New oil pump. have you changed the pump after the blow-ups? Is
there a crack in the suck-side feed to the oil pump? Are all external lines
high pressure?
2. Oil pan. Is it different from before? Have you checked the oil
pickup height in relation to the pan?
3. Too much oil in the sump. One of the things that can happen with an
Accusump is that you if you start out with a certain level of oil in the
pan, the Accusump can tend to overfill it during the race - as the engine
heats up, pressure drops, the AS has high pressure oil, it bleeds oil into
the main system. then, the crank might whip the oil, causing aeration and
poor pickup, and then the bearings start to fail.
4. Consider a half-dry-sump system. Use the original oil pump as the
scavenge pump, feed a reservior which will de-aerate the oil and maintain a
stable supply to an external pressure oil pump.
5. Investigate your oil-pressure bypass system. If the system shunts
oil back to the sump if the pressure is too high (this is the main bypass,
not the over-pressure valve in some oil filters), then what may be happening
is that the system is developing too much oil pressure, it's all going down
into the sump, so you aren't getting the volume that you should be. Also,
it's possible that the bypass is sticking open - you get great pressure at
cold idle, but it all drains away when the oil is hot.
Hot oil pressure should be 10 Lbs per 1000 rpm max. I see about 50 Lbs hot
at speed, and the hot idle pressure is so low I don't idle it hot! I just
took the engine apart after about 20 hours, and the bearings are perfect.
The piston rings suck, the cam was wiped, the rockers need work, but the
bearings were perfect...
Cheers, and let us know if any of our ideas sound promising..
Brian
At 09:11 PM 7/10/99 -0400, you wrote:
>I'm stumped and so are all my friends. Have Volvo, B18 (1800cc) full
>race engine, Oberg filter, Accusump, baffled pan and big oil cooler,new
>high pressure pump. I'm on the third engine this year (one per race).
>Runs fine initially then eats both main and rod bearings.Engine is
>properly clearanced including endplay by a professional builder who is
>also at his wit's end. We have checked crank for straightness, line
>bored the mains, balanced and rebalanced the crank and entire
>reciprocating assembly and we still get bearing meltdown after, say an
>hour or so of racing. Assembly and reassembly are done under almost
>"clean room" conditions.Holds 80 lbs. of pressure at idle when new then
>drops when bearings start to go. Ran well at Mosport this past weekend
>and held pressure until last race when warning light went on and
>pressure was at 30 lbs. and going South. Oil temperature has been high
>at 240 - outside temperature was over 100. Oberg is full of bearing
>remains. We have also checked all passages for restrictions.There are
>approximately 7 quarts in the system. I run the engine above 7200 rpm's
>but have been doing that for twenty-five years without this kind of
>problem. Anybody have any ideas short of demonic possesion? I keep going
>back to the Oberg - cooler - Accusump circuit eventhough this setup has
>been on the car for five years without problems until this year. No
>notion is too wild. Winning idea gets team T-shirt and a percentage of
>saved psychiatric bills. Thanks in advance,
>John Hamilton
>
Brian Evans
Director, Global Sales
UUNET, An MCI WorldCom Company
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