Hole in piston

[crownlinekid]

99 770L ,best synthetic oil,gas treatments,fuel line filters,oil line filters,washes,waxes,new spark plugs twice a year,correct winterizations,still hole in number one piston,is this commom?

[ADub]

Re: Hole in piston

Did you ever rebuild the carbs. Even with zealous maintenance, carbs still need to be rebuilt. Sounds like one of yours went lean and burnt a piston.

[dank]

Re: Hole in piston

Not a normal failre for a 770 engine.

Need to pressure check the engine to see if the crank bearing or cases have an air leak.

It could be the carb also but it would have to be very dirty inside or the internal filter is cloged.

[crownlinekid]

Re: Hole in piston

Bought ski new,single carb,seals on pump saft went south,bought new OEM seals did not like,machined pump housing myself,installed back to back seals like IOs,is this just a bad ski?

[John Kubiak]

Re: Hole in piston

99 770L ,best synthetic oil,gas treatments,fuel line filters,oil line filters,washes,waxes,new spark plugs twice a year,correct winterizations,still hole in number one piston,is this commom?

Gas treatments/fuel additives are normally NOT RECOMMENDED FOR USE IN TWO-STROKE PWC ENGINES as they dilute the oil, and may cause the engine to fail prematurely due to excessive bearing or piston/cylinder wear.


Although washing and waxing a ski is a good idea, it has absolutely nothing to do with keeping the engine internals together!!!

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Your answer may be right here!

Did you ever rebuild the carbs. Even with zealous maintenance, carbs still need to be rebuilt. Sounds like one of yours went lean and burnt a piston.

It is possible that the fuel system and the fuel selector valve needs a thorough cleaning as well as the carburetor!!!

[crownlinekid]

Re: Hole in piston

Thanxs for insight,fuel treatment was last year.Love looks,ride,feel, of ski,do not understand why low hour ski does this. At LakeOzark,everyone says I take too good care of it.Cylinders are good,colors are good,total rebuild? Or topend and find air leak?All help will be greatly needed.

[dank]

Re: Hole in piston

Not much of a chance the cylinders are in good shape after melting a hole threw the piston unless you are useing the wrong plugs. Should be a BR9EYA or BR9ES.

[crownlinekid]

Re: Hole in piston

I am going with premium pak,SBT needs my shortblock to rebuild,does porting intake exhaust help any or just time lost?

[Bill O'Neal2]

Re: Hole in piston

When I get a watercraft in my shop with a hole in the piston, I must find out why it got a hole in the piston before I can expect to fix it and have it not burn another hole in the piston again. Failure to do so, will result in possibly just having to do the job again.

What causes a piston to get a hole in it.

Most commonly, a too lean fuel to air mixture coming through the intake.
How does this happen?
Most commonly, a dirty carbureator(s) or a clogged up fuel selector valve. Next could be such things as a clogged up screen in the fuel tank fuel pickup, or an air leak because of a loose hose clamp on a fuel line. Anything that might impare the flow of fuel from getting through the carbs and into the motor.
A very common problem on two stroke motors is an air leak into the engine. It could come from something as simple as a bad gasket under the carb, or a cracked intake manifold or air leaking around the reed cages, or it could come from a worn out engine case seal such as the seals located on each end of the crankshaft.

An easy thing to check is the indexing of the crankshaft. This can be knocked out of kilter by gulping some water into the intake system while riding the watercraft, especially after a roll-over.
A two clyinder engine has two pistons timed 180 degrees apart on the crankshaft rotation. So, one piston should be at top dead center while the other is at bottom dead center. If not exactly 180 apart, the ignition timing is effected and that can cause a hole being burnt into a piston top.
A three clyinder motor is spaced at 120 degrees apart, so if the middle piston is at TDC, the outer two pistons must measure exactly the same distance down in their clyinders. It is fairly common to find a piston with a hole in a three clyindered motor, as the crankshaft of a three clyinder motor is much easier to get twisted from a hydrolock than is a two clyinder motor.

If your problem is not carbureator or fuel related and you have no air leaks from the fuel lines or from under the carb or through a gasket somewhere, then an SBT engine will come with no air leaks due to case seals and it will not have a twisted crankshaft. But if you install that new motor and do have a problem with one of those bolt-on parts, like the carbureator or fuel system, you will see the same failure over and over until you fix the problem.

I highly doubt it will be from using the wrong heat range sparkplugs.