951 Rebuild / Disaster / Advice needed

[electroryan]

I brought a 951 xp ltd 951. i was stupid not to compression check it . it had low compression.

i stripped the top end. Pistons said 87.91 . people told me can only get 88mm and its the same thing. brought a wsm rebuild kit.
Bore looked clean and no damage. I had a mechanic friend check the tolerances of the pistons ( without rings on ) with a feeler gauge.

put new pistons on and rings and oiled them all up . I used hose clamps to line up rings and slowly slid clamps of when got into the chamfered part of the block. I checked many times to make sure the rings were lined up and that the pins and rings lined up in the right place either side of the exhaust port . you could tell by looking down the exhaust ports.

oiled all components as putting together, slowly turned it over by hand and pistons ran up and down nice. greased gaskets and put all together nicely and torqued up head as per specs.

turned motor over a bit with starter motor running. maybe 6 seconds at a time then waiting a few mins , put bit more oil down spark plug hole. All was going well.

hooked leads up to plugs , proceed to do the run it to bed the rings in .

primed with petrol and just started run on its own spark , then klunking noise and it stalled.

took out power valves and looked down and ring had ripped off and top of pistons missing on both sides.





stripped all back down. metal fragments through reeds and in crank case.

i just dont understand what the hell happened . did the power valves catch on the rings ????

lots of pictures below.

i dont know how to proceed now. please help.

 

[purple_people_eater]

first thing is first, get that thing pulled and on a bench. take your mono-block (jugs/cylinders) to machine shop and have them measured to make sure they are not out of round and are within spec, if necessary have them bored 0.5mm over and order the new correct size pistons/rings. if you bore the cylinders, you have to shave the rave values 0.25mm.

separate the lower cases and clean out the metal shavings. inspect the crank and counter-balance shaft bearings and make sure you haven't damaged them, if they catch so much as a little bit, they're gone. if its all ok, after cleaning the cases reinstall the counter-balance and crank, seal the case halves with threebond 1194/1204.

install pistons (with or without rings) and the place a standard size base gasket on the lower end. install the mono block and head and head gasket, lightly( a little past hand tight) torque the head down using the nuts on the long studs that run up through the mono block. test now check your squish clearance (this is where i think you went wrong before.) stock spec is 1.7-2.1mm. adjust accordingly with the base gasket and remeasure. when you're within spec, lightly coat both sides of the base gasket in threebond, reinstall everything for the last time, light coat head gasket sides in threebond and torque following the factory torque procedure and specs.

 

[SabrToothSqrl]

I assume NZ is New Zealand?

In the US we have dozens of shops that will rebuild your engine and give you a 1-2 year no fault warranty on it. ($1200-2,000) USD

Are there any near you, in NZ?

The 951 is one of the more difficult engine rebuilds, and at 16 years old you should really rebuild the entire engine.
Just doing "just a top end" on a high performance 16 year old system often results in failure within 1-2 seasons. (as you've... seen...)

I'd search for a place that will give you a warranty, or start buying parts and read, read, read, read... these are high performance tight tolerance engines

The XP is wicked fun though. I had two up until last week. (sold one).

 

[dps]

Pistons were put on backwards and the top ring caught exhaust port

 

[dalef62]

Pistons were put on backwards and the top ring caught exhaust port

That what I thought too! If the ring joint is in the port it will catch.

 

[mikidymac]

There are a few issues that were already mentioned. The pistons were installed backwards. The arrow always faces the exhaust port so your ring gaps are not in the exhaust port. The way you installed it the gap was in the port and the rings caught the port and trashed everything.

Any markings on the rings always face up as in you should be able to see them when looking down at the top of the piston. It is typically a "r", a square or a dot.
Also your base gasket looks used. Never reuse a gasket especially on one of these high performance engines.

That engine will have to be torn completely apart to inspect for bits of crap in the crank bearings.

 

[Minnetonka4me]

LOL Glad dave chimed in!!! I saw that right away too.

 

[tobytd]

Not seeing any chamfer in ports

 

[Sportster-2001-951C-Stock]

Ring end snag in port window. Also check for poor chamfer around port can cause ring snagging. If cylinder was rebored sometimes the machinist doesn't chamfer the port b/c it takes time, he leaves that for the builder (some builders are fussy about chamfer shape and prefer doing this themselves).

And yes, make sure to measure minimum RAVE clearance. I think this spec is given in service manual.

 

[electroryan]

NZ is New Zealand yes. for a top end rebuild here it costs the equivalent of $2200 US.


There is not a huge variety of shops like in the states.

Thanks for you help . im really pissed off now , mentioning the pistons look backwards. i checked original photos of taking engine apart and they are with out a doubt backwards.
my mate who installed the pistons on the con rods is a mechanic of 30 years and used to be on a team of F1 racing. Unbelievable!!!! I would of done better off doing it my self then i would have sure studied all original pictures and consulted the workshop manual word by word!

I had got a rebuild kit from California for $300 US. I guess now i need to split crank case and remove every bit of metal so doesn't screw bearings.

thanks a lot for your help. have to save some money and do the hole thing again , shit

 

[Minnetonka4me]

That sucks man...Yup if you did it at least the only person you could blame is yourself.

 

[Coastiejoe]

NZ is New Zealand yes. for a top end rebuild here it costs the equivalent of $2200 US.


There is not a huge variety of shops like in the states.

Thanks for you help . im really pissed off now , mentioning the pistons look backwards. i checked original photos of taking engine apart and they are with out a doubt backwards.
my mate who installed the pistons on the con rods is a mechanic of 30 years and used to be on a team of F1 racing. Unbelievable!!!! I would of done better off doing it my self then i would have sure studied all original pictures and consulted the workshop manual word by word!

I had got a rebuild kit from California for $300 US. I guess now i need to split crank case and remove every bit of metal so doesn't screw bearings.

thanks a lot for your help. have to save some money and do the hole thing again , shit

Things happen for a reason... Lets hope that in doing the extra work you are resolving another issue. Sadly, life is a live and learn event.

Good luck with it all.

 

[pivotworx]

I always pull the engine!!! I just did a 951 with hotrods crank and prox pistons. Machine work and all parts I was right at 1000.00 this ski runs amazing!

 

[Sportster-2001-951C-Stock]

If you found metal in the crankcase the bearings are more than likely contaminated. Not sure I could trust them, if a broken rod occurs your good case will have ugly new windows.

Always double check on any 2-stroke the ring ends will not be exposed to the port, it's too easy to have mismatched parts b/c sometimes manufacturers will move the ports (for whatever reason).

I'll admit I've occasionally forgotten to check this myself and I've always been lucky despite not checking.

 

[bajaman123]

On the plus side, you have a great opportunity to replace those TEMPO fuel lines...