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Post by Henrik on Jun 26, 2003 10:19:38 GMT -5
Hmmm, just spoke to the kart shop about the repairs, and it turns out that there was a certain chain of events in the engine that lead to the overheating.
One of the exhaust valves got stuck open due to poor lubrication, resulting in the cylinder head gasket to blow, and the cooling water entering the engine. Thus a sudden drop in the cooling system water volume, and the overheating.
Now, the question is what caused the poor lubrication? I'm hoping maybe one of you can provide some thoughts. Personally I am beginning to believe it was a result of the very high temperatures we had that day, and possible the oil not being viscous enough for those conditions. Any thoughts?
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Post by Wycco on Jun 26, 2003 12:07:24 GMT -5
Now, the question is what caused the poor lubrication? Any thoughts? You really don't want to know my thoughts!
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Post by CFF on Jun 26, 2003 14:19:04 GMT -5
Henrik: While there are many reasons you might have lost lubrication to the valve(s) that caused your engine to overheat (fail??), without knowing the specifics of your engine it's hard to say (I've garnered that it's some sort of higher performance engine, but not being a cart type I don't know exactly what you run). What sort of valve actuation does it have? More importantly, I'd guess it does NOT have a dry sump lubrication system, and the description of you getting up on two wheels numerous times gets me to wondering if you simply lost oil supply. You don't want to be running the engine for very long when your head is closer to the ground than the crankshaft Even worse though, if your valve(s) was stuck open, are you (they) certain you didn't damage (hole) your piston? CFF
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Post by Henrik on Jun 26, 2003 17:24:30 GMT -5
CFF,
It is indeed a dry sump. I'll get some more technical details on the engine up here soon, but it is 250cc twin 4 stroke (obviously with the valves!!) with a max rev of nearly 14'000. In that specific race, I would say I would be running at between 10'00 and 13'000 rpm's most of the time.
As to other damage, I am afraid there probably is. I'm looking at the pistons and the cylinders in more detail tomorrow......
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Post by raptor22 on Jun 26, 2003 17:48:25 GMT -5
can you post some pictures of the components as well please. Let Shamu Engineering Consultants solve your problem More importantly please supply details of the oil, oil filter type and all those other things I mentioned in my PM to you earlier. Gut feel tells me it's just oil starvation but the origin of that may be tricky to solve.
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Post by CFF on Jun 26, 2003 18:43:33 GMT -5
It is indeed a dry sump. I'll get some more technical details on the engine up here soon, but it is 250cc twin 4 stroke (obviously with the valves!!) with a max rev of nearly 14'000. In that specific race, I would say I would be running at between 10'00 and 13'000 rpm's most of the time. Henrik: Is that a modified motorcycle engine then (Honda, Kawasaki)? Would I be wrong in guessing that it's DOHC? Regardless of what the shop tells you, when you hear about (exhaust) valves "sticking" open, you generally are looking at either a faulty or underspec valve spring. This would be especially true for a higher RPM engine that may (or may not) have aggressive cam profiles. Can you say valve float?? *sorry - not a great diagnosis, but under the circumstances ....*. Any chance that during one of those ~corners~ where things got all tippy (or perhaps when your heavier buddy broke the chain) you exceeded the redline? CFF
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Post by raptor22 on Jun 26, 2003 18:57:46 GMT -5
yeah but a sticking valve won;t make the engine overheat, it'll just run crap. The valve couldbe sticky due to the fact it got bent when the engine redlined at chain snap, but this is more than likely unrelated to the overheating problems.
have you had the radiator checked for any looes solder than could have blocked a water chanel? The solder can break loose with the vibration and impacts that go-kart sees
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Post by Henrik on Jun 27, 2003 1:55:17 GMT -5
You guys are great! I supose my problem now is you are asking all these questions that I can't answer! LOL!! Okay, I'll give you some more feedback about the engine. I take it Raptor you already know a bit about it, but for CFF's sake, I'll give you the background. The engine is a Biland SA250 ( www.kart-power.com). It has created by Rolf Biland, a Swiss former side-car racer (I think 7 times world champ and a real innovator). The basic design was created a few years back in attempt to bring 4-stroke power to karting. The idea was to make an engine of the same weight as the 2-strokes, producing more or less the same power, but with the obvious torque increase. I would say they have succeeded! Okay, here is the basic tech daat: Engine type: 2-cylinder-4-stroke straight 2 engine Cooling system: Water cooling system Cubic capacity: 248.35 ccm Bore: 58 mm Stroke: 47 mm Compression: 11.2 : 1 Ignition gap: 180° / 540° Cylinder head: 1overhead camschaft, 2 valves per cylinder Valve gear: Cup valve push rods with compensation discs Toothed drive belt Pistons: forged aluminium pistions with 3 piston rings Con rods: forged steel Prob shaft: forged steel Clutch: fly wheel with centrifugal clutch Lubrication: dry sump system Carburation: 2-Dell'Orto Carburetors with cacuum pump Fuel: Euro unleaded: ROZ 95 Weight: 15 kg approx The more I think about the problem though, I think it is down to there simply not being enough oil in it. What I am having a problem with is why it was spewing out oil. Here I'm thinking that it was the temp that caused this, and possibly an oil with a higher viscosity could have prevented this problem. I need to get some more info from my mechanic today, and I'll post the results up here. Again, thanks you guys! Here's a round for you:
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Post by raptor22 on Jun 27, 2003 5:27:14 GMT -5
HI Henrik,
Yes a higher viscosity oil will help, but mor important is the Viscosity index. All this is, is the ability of the oil to maintain a constant viscosity throughout the operatign temperature range. typically 10W50 or 10W60 would be ok.
Another thing is, the oil should be a High VI (Viscosity index) oil developed for motorcycle engines. Passenger car oil is not formulated for small light engines. If you're using a synthetic then this is less of an issue.
Now although the oil contributes significantly to the cooling of the engine, the water jackets and radiator are still the most important contributors. If it was a Lube temperature problem, perhaps fitting an oil cooler would benefit. It will increase the oil volume and help to bring down oil temp on hot days.
All that said I'm still grabbig at straws. Hope you can post some pics of the engine components soon.
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Post by CFF on Jun 27, 2003 9:00:29 GMT -5
Raptor (Henrik): After looking at the engine specs, and visiting the website, I'm left scratching my head. Help me out here. How can a motor have BOTH an Overhead Cam AND Pushrods? Perhaps what they meant to say was it had overhead valves (OHV)?
CFF
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Post by daSilva on Jun 27, 2003 9:56:49 GMT -5
Actually I would recommend a 20W50 synthetic for summer racing. What viscosity are you running now? How often are you changing the oil? What sort of break in did you do on the engine?
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Post by raptor22 on Jun 29, 2003 19:09:08 GMT -5
I would not recommend a 20W50 for any kind of racing, especialluy in a small 250cc engine.
CFF, I suspect the push rods they're refering to are in actual fact the rocker arms. Or does the engine utilise some kind of articulated valve displacement mechanisms???
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Post by Henrik on Jul 7, 2003 10:01:57 GMT -5
Okay, received a verdict from the Biland factory.
The damage is not too extensive in the end. One exhaust valve that has been bent and needs to be replaced, and the cylinder head gasket. Biland is saying that the valve was damaged/bent through an over-reving. Now I'm very surprised by this (I'm no JPM!!!), because I can't recall over-reving the engine. Also, I thought it had a rev-limiter. Also, that would imply that I ran the kart all Friday and Sunday with a busted valve!! Now, apart from the strain that would have put on the engine, I can only assume that it must have reduced the performance, and so my lap times were actually really good!!!! Anyway, that is what they say, and the damaged valve then caused the oil to be spewed out in the expansion bottle.
I should be picking up the kart this weekend, and I'll try to make some photos of the pieces to post here.
About the oil, they are now suggesting a 15W40 or 15W50 during summer, as opposed to the 10W40 or 50 originally recommended. I'm getting the feeling they know as much as I do!!!
I suppose I'll have to finish the season with the kart as it is, but this winter I intend on trying to hook up an oil cooler to it, and then see if this can be accepted by the regulations. I think in any case it is a good idea to have an oil cooler on such an engine.
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Post by raptor22 on Jul 7, 2003 16:52:15 GMT -5
sounds very plausible however the oil recommendation is'nt to far of the truth. Although for winter I would not go for 15W 40, rather a 10W40 or 0W30. just make sure the lower viscosity range is below the 20W classification. I feel thats too viscous for use in such a light engine that it will probably cause overheating anway due excessive shearing of the oil.
I'd say try a 0W30 in winter and a 10W40//50/60 in summer. perhaps a 15Wsomething if you're hard pressed to find the others.
not too concerned about the summer classification, but the winter classifaction MUST be below 20W
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Post by Henrik on Jul 7, 2003 17:07:25 GMT -5
Raptor,
I was sort of thinking the same about the oil.
However, it does bring me to ask a question that I have been wanting to ask for a long time....
What do those figures actually mean? I know the difference between say a 10W40 and a 15W40, but what do the numbers really stand for?
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