Yamaha Blood
New member
OK I bought a 1979 SRX in a basket and have been trying to get it running correctly, but melted two sets of pistons now. The first time the pistons flashed I thought it was caused by a combination of under jetting , fuel supply problem and or crank sealing. So I completely dissassembled the sled. Rinsed the tank, new fuel lines and filter,pumps rebuilt, cleaned carbs spottless, made sure floats were set correctly and all circuits were clean and with correct jets. Intake manifolds are OK but not new. Installed new crank seals, bearings all looked good. With new rings the end gap is on the large end of the spec, because I've had to hone and clean cylinders up a couple of times. I've just noticed that the heads look to have been milled, (never noticed this before) maybe about 30 thou. The timing is set correctly within spec. but I'm missing the exhaust gaskets in the manifolds. The mag piston dome has melted and formed a layer of aluminum on the head, directly over the exhaust port. I believe that either poor fuel or too low octane caused the flashing. The cyl walls and head are covered with a thick oil glaze like syrup. There was a small pool of this oil on pistons above melted areas. I mixed 100-1 Ams-Oil to 20:1 using fresh pump 91. The Mag side had slightly more compression than the PTO side which is the side that failed. PTO side just starting to round the piston dome circumference at the ext port area. It turns over freely but is sticky throught the full rotation. Can't feel when the flywheel passes the stator. Bottom end is OK. It only ran for about two full hours, but went like hell. Engine failed during trail blazing in fresh snow 3/4 throttle about 7000 RPM, so the engine was under heavy load, which explains the detination. All jets sizes are per spec, and mains are 340. The whole sled is completely stock with the exception of the milled heads (just noticed or would not have run pump fuel). Am I correct to say the flashing was caused by too low of octane ? Can someone please explain this oil mess and glazing? Is the Ams oil separating and mixing with the flash material or is it coolant getting sucked in? What am I missing? I can't seem to load the pictures to this post. Getting frustrated. Really appreciate some help right about now.
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were you running with the air box. is the power jet circuit operating properly. low octane will kill these engines, espically if the heads were milled. what is (was) the compression ratio. i bet that thing ran like a scalded dog just before it stopped. they always do.....
Yamaha Blood
New member
Air box and boots are all installed correctly. I replaced the power jet hoses and the power circuits were clean. I wish I could load more pictures, but sled is spotless except near the exhaust manifolds where all this oil mess slobbered out. I'm sure the piston failure is from lack of octane, but what is all the glazed syrup like residue and black liquid from? You can see the black liquid pooling at the top of the mag cylinder where the ring stops, and it's pooling now on the head near the spark plug threads. It's accumulating there from sitting up side down for a couple of days, but was a residue over the complete chamber surface when I first removed the heads. The pistons are 40 over (69.5 mm) which I can't find anymore. The compression was about 130, and 135
so the cylinders have been sleved and heads milled. any exhaust port work done. after you find parts id jet up a couple. maby even more. its better to be safe than sorry. i wouldnt worry about the oil mess. maby cut back on the oil some. book calls for 15:1 ratio, thats a lot of oil and the more oil in the gas the less gas getting through the jet (actually a lean condition). todays gas and oil arent what they were 30 years ago. the oils are better and the gas is worse. hope this helps...
opsled
Active member
Orange goop not nessessary if things are right,
Outside waterjacket o-ring looks good. Cylinder ring does not. Cylinder o- ring is more important.
Sleeved?? If so you probably have a cylinder o-ring grove depth problem.
Seen this with sleeved cylinders on occation. O'ring groove is to deep and won't allow good sealing. Coollant ends up it the combustion stroke and makes a mess.
My guess from what you've shown.
opsled
Outside waterjacket o-ring looks good. Cylinder ring does not. Cylinder o- ring is more important.
Sleeved?? If so you probably have a cylinder o-ring grove depth problem.
Seen this with sleeved cylinders on occation. O'ring groove is to deep and won't allow good sealing. Coollant ends up it the combustion stroke and makes a mess.
My guess from what you've shown.
opsled
peisnowguy
New member
Not sure but I would think you need the exhaust gaskets in the manifold. I am no expert on SRXs but if the manifolds are leaking, even a little, would this possibly lean out the engine? It is just a hunch but I think everything needs to seal properly, so the pipe is doing what it was mean't to do. I just know years ago running a sled engine without the exhaust manifold and pipe was a no no.
Yamaha Blood
New member
Yes, both cyl are sleeved. Some porting work on intake, exhaust, and transfers. Good tip on the O-ring groove, thanks. The orange is Ultra-Copper high temp sealant. We use it on the intake manifold of the drag cars rather than the rubber gaskets that come in the kits. When she ran it worked really well. I'll bet it would give my old 83 V-max a good run for it's money. So it may be sucking in some coolant..aaah. I know coolant can make a sticky mess sometimes, which gives me the confirmation I was looking for. Thanks for the help guys.