SJ 701 engine overheating

[FMT]

problem need some solution
I had an overheating on 701 engine, 81.5 piston , factory B pipe dual cooling system , TDR water box , and ADA head
the problem started after 1hr riding and the cooling system was ok , once the engine got overheating I switched off
and now the pressure on the rear piston is 0 ,front is 150 PSI
oil mixing was ok ,the engine was working good before one day
IDK why the engine heated , if someone can clarify to me the specific reason

 

[jetskidude1113]

first, we need to know how is your cooling routed?

 

[mikidymac]

You have bigger issues than overheating if your rear compression is 0.
Dual or single carb?

 

[aboarder]

You're going to have to open your engine so we can find out whether the heat was result of a blown piston, or the blown piston was the result of heat

 

[FMT]

first, we need to know how is your cooling routed?

2 line from pump to the manifold , line from b pibe to the head and line from the head to outside

 

[FMT]

You have bigger issues than overheating if your rear compression is 0.
Dual or single carb?

Dual , yea i know

 

[FMT]

You're going to have to open your engine so we can find out whether the heat was result of a blown piston, or the blown piston was the result of heat

I will

 

[john zigler]

I am going to guess a lean condition = heat, witch lead to piston failure. Either a carb/fuel problem, or air leak, crank seal, etc. Do a leak down test before you disassemble your engine.

Could also be detonation from wrong fuel type, too much compression, timing advance, etc.

 

[fastgtfairlane]

i dont think you overheated. sounds more like a lean seize. i just took apart a 62t 701 out of a raider that had overheated enough to turn the stock gray cylinder head a nice dark bronze. both cylinders had 4 corner seizure but engine still had compression once it cooled off. since yours has no compression on the rear and decent on the front, yours sounds like a different type of failure. such as an airleak. probably not due to bad gas i think both cylinders would be bad then. you could also have a crank bearing starting to let go on the rear cylinder causing a seizure. had that happen before.

 

[EB18]

Do a leak down test (as mentioned above) before tearing that thing apart. Once pressurized listen to the carb, exhaust and around the engine to see where the air is escaping. Engines don't overheat for no reason. I'm assuming your cooling setup was fine and that this wasn't the first hour you rode it. Sound like an extreme lean condition. Engine should hold 10psi, if your crank seals are blown they'll let air in and lean you out = failure.

It's important to find out why it went wrong. Damage is done. If you can trace it back to something as simple as crank seals/ etc, after your rebuild you can ride in confidence knowing the problem is addressed.

 

[smoofers]

You burned a hole through your rear piston due to a lean condition. Either an air leak or or a leaky carb fuel circuit.

 

[bored&stroked]

No way a properly working dual cooling system engine overheated with both lines going into the engine. I don't overheat a more modded single cooled engine in 115* air and 80's water temps.

 

[kevbo]

Did you ever confirm your main circuit was set rich of peak rpm? Did you open the top screws to compensate for cooler air? Are you sure the gas was good? Any one of these factors alone will stick a piston. At this point, you need to remove the engine and inspect/repair everything. Start with carbs tuned way too rich and work leaner as the engine gets some run time.