Reuse crank and counter balance - engine under 100 hours

[tkarvelis]

Typically I have read that you should replace / rebuild the counter balance and crank over 200 hours. I recently purchased a DI engine that had I believe 80 hours. The crank and CB look great, bearings are smooth.

The mag piston appears to have lost a ring or something and took out an edge of the rave, and banged up the head surface.

Should I be concerned with the possibliity of comtamination from the rings / metal? If so, what should i clean it with?

I was planning on selling my 95 GTS and use the profits to build the DI, but my 12 year old daughter took to jet skiing like a fish to water... and has claimed it

 

[AZ Sea Doo XP]

i have been told many times the 951 are only good for 200 hours. i have seen them over 400. the balance/crankshaft should be very good at 80 hrs. the issue of metal filings would be a concern, as would be the cause of the ring failure. good luck!

 

[stang69]

Dependant on how much debris is in your crank, you will be fine with your original crank. A couple of years ago on my 03 DI, I lost my PTO Cyl. Turns out the top compression ring spun 180 Deg. and it caught the Rave valve and broke a chuck off of it and busted a chuck of the top of the piston just above the ring grove. The piston ring lock pin in the ring groove was gone so the piston ring rotated until the split end opened up and caught the rave valve in the exhaust opening. Motor had 230 hours on it so replaced the crank with a hot rods crank, honed the cyls and put new std size pistons and rings back in (No scoring to cyl walls)Got over 140 psi on both cyls. Earlier this year, my wife's 03 DI lost the Mag cylinder and after a compression test @ 0 Psi, pulled the rave valve and AGAIN a chuck out of that one too. Rotated the drive shaft and top ring had spun and broke a chunk out of the piston when it caught the rave on the down stroke. Hers only has 160 hours on it. Haven't touch it since - Bummer Curious if this is an ongoing issue with the 951 DI's. Worked on a bunch of Rave valve motors but never seen anything likes this except both of mine and possibly yours.
Have a look at yours and see if the piston ring is bent upward, if it is your cylinder wall should be fine and just a quick hone and there should not be any debris in your crank. Good luck:thumbsup:

 

[nhmort]

My question, is it necessary to rebuild the bottom end if there was no top end damage?

I understand that the oil seals may be of concern to some.

I'm going to rebuild my top end this winter. I almost have 200 hours. It's preventative for me. I also think my top end is tired. I can only get about 6300rpm out of my 951 DI these days.

What do you guys think. Has there been any real world experiences with not doing the bottom end and then having troubles?

I know that Doowacka hasn't done his bottom ends from his past threads. He has four of these skis.

 

[Coastiejoe]

General rule is, if there is 300 hours on the crank, you need to rebuild everything. Below 300, the crank can normally be used again.

High hour cranks, do not normally hold up when you replace the top end.

 

[AZ Sea Doo XP]

6300 is low. what is the compression? is the air compressor working properly?

 

[nhmort]

I have 115 on both mag and pto.

I believe that 120 according to some guys that have recently re done the top end is what they've been getting.

That seems low to me though.

What else causes low rpm under load in the water? I can hit the rev limiter on the trailer.

 

[mikidymac]

The DI engine should have a cranking compression of 145-140, the carb 951 should be 130 and 951's are done at about 110. 115 is getting very low for a DI in my opinion.

 

[nhmort]

Sounds like a new top end is in order.

Thanks guys.

 

[mikidymac]

At 200 hours on a 951 I would be replacing the crank too. That is just me.

 

[AZ Sea Doo XP]

I think 115 is too low. i heard carb engines had higher compression than the DI, I have no info to support that. I had both. I cant remember what the compression was on the DI. i have heard that the 951 must be rebuilt at 200 hours, crank included. I ran my carb 951 to 400 hours with no crank problems. I did replace the pistons once. you can check the crank clearance when you remove the pistons and make the decision then. dont forget to regularly check the balance shaft oil!!!!

 

[nhmort]

Thanks for the great information guys.

 

[nhmort]

After reading this again, how is the crank clearance checked? Is that by squish?

The manual says you should be fine if you replace the gasket with the identical one by reading the size.

 

[AZ Sea Doo XP]

this is a page from the SD manual. it can be done with the crank in the engine. there are other measurements that should be done but cant unless the engine is out and apart. I would get other opinions. I hope this helps!

 

[mikidymac]

A... no. Although the measurements are provided there is no easy way to see if the crank bearings are at the end of their life. Anything over 200 hours should be replaced.

A carbed 951 should have 130 psi compression and a DI should have 140-145. At 110 they need to be rebuilt.

 

[AZ Sea Doo XP]

if SD cant make an engine go more than 200 hours (mine went 400) then people should sell them and buy something else that is made better.

 

[mikidymac]

if SD cant make an engine go more than 200 hours (mine went 400) then people should sell them and buy something else that is made better.

The issue is the owner not the ski. Seadoo got wrapped up in the horsepower wars and didn't want the complexity of a three cylinder engine. The 951 makes more power per cubic centimeter than most any other 2 stroke so it is a high performance highly stressed engine.

The issue is owners that do no maintenance, use the wrong oil, flood them and put them away wet. This causes the generic answer of it being done at 200 hours. If taken care of they have been known to get well into the 400+ hour range. Unfortunately the general public doesn't treat them as they should.