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jlaird

jlaird

Great Pumpkin
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yamaha 1200 CC engine in a Ledgend race car.

Starts great, runs good, down on power.

35 to 36 lbs compression in each of the four cylinders.

Will turn to 10K no prob, no real power though, sounds smooth and good but not agressive like it should.

Engine is sealed by authorized rebuilders.

Egn is solid state and checks good, no fuel starvation problems. Four carbs.

What the heck?? Compression is low because? Timeing is off a tooth?

Any ideas welcome, this really has me stumped. I just can not find a reason. Maybe 200 laps or so on a fresh rebuild and it has never had good power at the top end.

Wing it guys.
 
Jack - think the guys over on the Racing Forum might have an answer?
 
Did it always have such low (and even) compression? Sounds to me like they have the wrong pistons (too short) in there.
Bill
 
Jack how much time is on the motor? It sounds like a valve problem. If a new ingine is broken in over a period of time, the valves must be reshimmed (they don't have adjustments but differnt shim thickenesses you put in under a cap to get the valve lash right) When the motor gets hot the valve lash increases and the valves wear into the seats just a few thousandths,but due to the increase lash when hot the motor still runs good, then when the motor cools back down there is no valve lash at all and the valves are held open just a thou or so. To check, blow compressed air in a spark plug hole and prssurize it and listen at the exhaust and intake for air. If you hear air then the valves need to be reshimmed. They sell shim kits for this or you can make something to lap them yourself. They are about the size of a watch battery. Once, reshimmed you should not have to do it again because it is now broken in. I have seen this many times, where someone buys a new motorcycle and does not have the break in service done like they should.
 
I'm not familiar with that kind of racing. Never heard of not letting you perform maintenance on your own engine. Don't think I would like that at all. That is 1/2 the sport, fixing your own engine. T'is how we evolve and learn how to get more horsepower, more efficiency. Plus the 1200 yammer sounds like a v-max engine and has its own set of issues that need to be looked after. Sounds like a sweet deal for whomever is building the engines though. I hope it comes with a warranty.
 
Noop no warenty no nothing. But the engines are awsum and run great.

New on going in as we speek then will have the tired one rebuilt.

Sat nite we loaded for bear.
 
*But the engines are awsum and run great.*


"35 to 36 lbs compression in each of the four cylinders."


*New one going in as we speek then will have the tired one rebuilt.*


"Maybe 200 laps or so on a fresh rebuild and it has never had good power at the top end."

I think I would be shopping around for a new "authorized rebuilder".
 
Yep, that one got busted for cheating. Unauthorized mods for his buds.

This one will go to the factory in Charlot NC, the heck with rebuilders. We going to the builder. Would love to have a dino run on these engines before putting them in the car and paying for them but is not in the cards.
 
Legends are spec racing guys, kinda like SCCA's Spec racer, meaning almost every part on the car has to be purchased from 600 racing in Charlotte or a authorized dealer, the engines are sealed and you can't touch them. Spec racing has became huge with the masses for obvious reasons. Jack, since you can't touch it, there's not much use to worry about it, send it back to 600 or run it. This is your neighbor right Jack, if he's in the market for another car with a buttload of good spares for a deal, let me know.
 
You would think that the builder would include a break in maintenance in the price. motorcyle engines got to have that one service after break in. I would enquire about that or you might be in the same boat again. Since the engine is being sent back anyways, I would pull the valve cover and see if there is any valve lash.
 
Yep Hap, that's the deal. Oh we can tweek a bit to make sure everything is up to spec, but can not break engine seals and so forth.

My whole question etc. was to see if I had forgotten anything as my neighbour had the engine rebuilt last fall and thought it good but did not sound right to me, nor did it look right on the track.

But hay, I am not an expert by any stretch so came here to verify my thoughts.

The cars are so small that I can not get my legs in or I would have taken a few laps to make sure. 1100 lbs and smaller than Miss Agatha with three times the HP.

However, that all said I think I am a bit long in tooth to take laps except on a clear track, eyes not what they were nor are reflexes. But durn it looks like so much fun if you got the deep pockets for it.

Hap, if you have one for sale give me some specifics and I will spread the word down here at the track. They always looking.
 
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