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What part of the 951 cranks fail?

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68ragtop

68ragtop

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I have learned from reading so many posts here that the cranks on the 951's are over powered & shouldn't be expected to run more than 200 hours. Makes sense. For you guys rebuilding them often, what are you finding are their weakness's? I assume needle bearings? I would also assume that failure of these cranks is tightly related to moisture exposure over time.

I was planning on installing a rebuilt crank on this 951 I am building, but as I am checking & cleaning it. I am not finding anything wrong with it. I cleaned all the bearings & do not see any rust, putting, or discoloration on any off the balls or rollers. Deflection is under .001" there is no rod end play, they are straight & axial specs are within new range. Bearings spin quiet, & balls are spotless. If I had never heard of common crank failures, I would be reinstalling this crank with complete confidence.

The ski, has 128 hours on it, however I am not sure if this has been replaced before or not.

Thanks for the info, 68RT
 
Sounds like a keeper 68. My first one snapped a rod but the second bad one just wore through the little brass spacer washers on either side of the rod on the crank end.

Usually with the 787 and 717 cranks you can always find a bearing that sounds and feels worse than the rest. If yours checks out then run it. Good is good and replacement would be a lot of money to spend just for "piece of mind".
 
It's not that cut and dry.

The crank can be damaged from moisture, it can be damaged from physical problems (like a melted piston) or it can be damaged from heat. Also... since the crank is pressed together, your inspection was useless. Not trying to sound harsh... but it's the truth. You can't measure the crank pins, you can't measure how "Round" the big end of the rod is... and you can't really see the rod bearings.


With the 951... if you are in it, and it has 125 hrs.... AND you want it to last... do a proper rebuild.

We see it here all the time where guys try to do the basics, and then the engine scatters within a season.
 
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Its a touch harsh, but its the truth. Anything other than a rebuilt is going to be a crap shoot. The "house" always wins just depends on when.

Pitting is the biggest factor for sure.

It could last a couple of seasons if you are finding nothing.


The usual death of the 951 is water getting in the motor. Obviously it can happen on any motor, but the 951 is just too underengineered to last like a lower HP motor and the 951 has always had trouble with getting the 951 pipe totally sealed and not spraying mist at high RPM inside the hull. Thats the point of the "diaper" for the pipe, and the rubber deflectors in front of the air downtubes heading to the airbox.

Obviously if you find aftermarket flame arrestors thats a real bad deal on a 951 unless it has one way valves to keep the hull dry, and the pipe is perfectly sealed.

If you dont bend a rod gulping a huge amount of water thru the carbs, it gets compressed past the piston rings and puts a slight bend in the piston skirts. Then you have piston slap. Once its slapping, the metal is being lightly bent back and forth until the skirt breaks, the pieces fall into the crank, the crank tries to rotate it around the cases, and the fragile cases crack.

Obviously theres lots of ways an engine can fail, but in my experience of taking apart failed 951 machines, its the most common way I have seen.
 
Thanks for the info. That's what I was looking for. However, based on the explanation of common failures, it would seem that in those instances, a new crank isn't going to stop death by water spray either. While I can't see all parts of the needle bearings on the big end, what I can see though the oiling slots looks clean & un pitted. I don't believe this crank has been exposed to water yet.

I have no issue buying a new crank, as I do not corner corners on any engine rebuild.. Ever.... But, when I look at something that looks fine, & is to spec per the service manual, I have to question what I am accomplishing by replacing it.

Hence the reason for the post.
 
Run it till it stops!

I'd use the existing crank if I was going to build it. If you drop $300 on a crank, and the engine goes, taking it with it, it will be a lost cause anyway.
 
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Lol, :lol: except I already have nearly $800 spend already & the parts are still in boxes.

If it was still together, I would completely agree!

The guy who put this engine together last did the "basics" & it would not have lasted. Backyard rebuild at best.
 
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Only way to do an engine is replace it all, no sense in pussy footing around. If you put good parts in, and pay attention to the details, you'll build a good engine.

Go all in!

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I guess this is what I expected to hear based on the the 951 crank folklore here.

But still, going back to the original post, Is there something specific with these 951 cranks that fail? weak rods, big end rod needles?

So far, it sounds like the environment around the crank is what causes them to fail, & not necessarily a weak crank alone. if its primarily rust & top end engine debris, then its not much different than any other PWC 2 stroke is susceptible to. So maybe its that the 951's will tear the cranks up as soon as any of the above are present. I was just expecting to measure some sort of wear, see rust or bad bearings on this crank with the reputation they have.
 
I've seen dozens on Ebay with stripped counterbalance drive gears and a bunch with the small end snapped off a rod. So you better do the counter balance bearings too. For me when I build an engine it's all new, I know the longevity of it already. With a used crank it's a matter of when it fails not why. SHS has OEM reman cranks for $394 with free shipping until the 30th. Like you know, I'm not really down with paying some to build my stuff, warranty or not I don't care. You've been into enough 2 strokes to know what you're doing, you'll be fine doing the work yourself.
 
So I guess the bottom line with these cranks are, if the engine is apart, replace it.

While I have been building engines for many years, I am still learning all the different specifics with the seadoo's. I am never afraid, or too proud to ask questions. The day that happens, I will stop learning. I too, would also never have anyone build me an engine. I trust almost nobodies work except my machinists .

About 12 years ago, my mother-in-law popped the engine in her chevy blazer. It was bad, (rod through the block bad). So to get her back on the road, I picked up a GM crate engine. After getting it going, The engine had a bad knock, Tested everything on my end & determined it was in the engine & nothing accessory or trans related. GM pulled the engine under warranty, replaced the engine again & informed me that the engine had .010" pistons in a .030" overbore. So, this proved they measure nothing on these engines. Just slam them together. What an eye opener that was.

I spend so much time cleaning, measuring, & researching that I would loose money if I ever tried it for a living.
 
Shspowersports.com

You'll need to create an account and might need to call to be put on their buyers program for free. Just create an account and then log in and if you see two columns of pricing you're good to go. The is s $200 core that you get back when they receive your old one. The forum sponsored oem parts will match their price but I don't think they do the free shipping.

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I have ordered from them a few times before. I tried to call, but I am thinking they are closed. My call ends up in a voicemail box that is not addressed as SHS powersports. So, I emailed Jen to see if I can get it done that way.
 
She's no longer there, try her boss which is the link to the left of her email link, IIRC. I would assume he's getting her emails.

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racerxxx said:
She's no longer there, try her boss which is the link to the left of her email link, IIRC. I would assume he's getting her emails.

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Click to expand...

Just bought one. free shipping ends at the end of the month a 951 crank with free shipping is 420 plus 200 core fee which u get back when they get your core.


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1995hx said:
Just bought one. free shipping ends at the end of the month a 951 crank with free shipping is 420 plus 200 core fee which u get back when they get your core.


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Click to expand...

Woot! It's a great deal man, glad you scored Dennis

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There were some cheap new OEM 951 pistons on eBay. IIRC it was like 120 for a pair of oems.

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racerxxx said:
There were some cheap OEM 951 pistons on eBay. IIRC it was like 120 for a pair of oems.

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Ya I saw them but got a great deal on pro x sealed in a box I always wonder on what I'm gonna get from eBay. In total I have 900 in rebuilding this engine with a complete gasket kit new crank pistons and a bore job.


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Right on that's great, I have $845 into my 787, but that was with extra gaskets and a full set of extra OEM rings. Can't wait for more HX progress!

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1995hx said:
Just bought one. free shipping ends at the end of the month a 951 crank with free shipping is 420 plus 200 core fee which u get back when they get your core.


Sent from my iPhone using Tapatalk
Click to expand...
what crank did you buy? Andy just quoted me $492.99, same price as in the oem parts finder. Is it a hot rods?
 
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