1980 SRX 440 broken crankshaft

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silverrocket

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I installed a new Polaris drive clutch P85 #1321736 on my Mod 1980 SRX. The clutch bore had to be cut a little deeper to make it fit. Last weekend I was testing on hard pack snow and snapped the crankshaft. I'm trying to figure out what cause the crankshaft to snap. I'm running the 1 3/8 wide belt with stock secondary. Had no vibration, engaging at 7,000 and shifting at 10,000. Not the first time out with this clutch. I had to much track spin so I installed speed cleats (2 in wide by 1 1/4 h) and than the crank snapped. Want to install another P85 but don't want to snap another crankshaft. What is the part number of the P85 that will fit on the 1980 SRX crankshaft? What needs to be done to the clutch bore for the clutch to work? I had to shim my secondary with a total of 3 washers to get proper alignment. Do I buy the same p/n and have the clutch bore cut a little deeper to bring it in closer to the engine or is there another part number that will fit without having to machine anything?

P85 damage 1.JPGP85 damage 2.JPG
 

The crank is 36 years old. Probably had numerous clutches on it and pulled off of it. Probably many hard launches over those 36 years. Something will break eventually. It just happens. Not uncommon to snap the pto stub off on a modded motor with a wicked engagement from time to time.
 
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i did that years ago to a 79 srx i had with a 102 c comet. same thing, 6500 engagement and aaen race pipes that spin to 10,200. these cranks if not welded i believe can not take rift of high rpm. also could of been in your case the weight of that clutch along with the rpm you were spinning at. 3:16x (yammie tony)
 
Never had a problem at 10,000 with the 77 which always ran the stock Yamaha primary. I think you are right on about the added weight making the difference. One year of the SRV (82??) came with the much heavier stock clutch like the 81SRX and it used to waste the PTO end of the crank when you were coming on an off the throttle a lot even at 7,000. They were so heavy we were switching them out for Comets to solve the problem. I still have a couple of those old boat anchors laying around.

For drags we were always limited to 5000 engagement back in the day so a little less impact on the crank also.
 
I have a 108C and a P85 and they weigh the same. What is the weight of the 102C calibrated? I'm going to try another P85 and have it machined to move it closer to the engine. I really like the P85 Polaris clutch. How fast (MPH) is a mod SRX 440 on snow (660 ft) with good traction. My mods are: SSR cylinders (ported), 76 heads (165 lbs), 42mm Carbs, Aaen race pipes (rpm 9,900), 17/31 gears, P85 Polaris clutch, Stock driven clutch (machined cam), 1 3/8 belt, Hewtech CDI. I have NOS also but not going to try it until I fix the crankshaft issue. I don't know how fast mine is because my crank broke.
 
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IMHO it was just time and the pto stub just gave up .... it happens ... i run my 78 with a 80 bottom end and bring it in a 7200 all day and it launches very hard ... on our 78 mod with p-85 and cat secondary we have always brought it in at 7k plus and as high as 8300 still no issues after years of running it ....neither crank welded ........the pto stub just gave up .....another issue is harmonics can cause hell on a cranks even though you may not see it in clutch wear or crank wear it can cause weak spots .........just have it fixed and keep running it
 
Nearly impossible to break it when the clutch is properly installed no matter what you do. It very likely was not machined correctly and created a focus point that sheared it. Ask DRP what the correct clutch part number is.
 
I've seen many broken pto stubs on many different motors. To say its impossible is very misleading. Metal fatigues over time. 7k launches will accellerate that weakening. After numerous heat cycles, clutch installs, clutch removals, and hard acceleration......things just happen.
 
I didn't say it is impossible. Unless it was defective, you won't break it on that motor. In fact, I don't even think they can be bent. They are very over sized. Using a stock one on a 200+ HP four cylinder 800 coming in at over 7,000 RPMs on many surfaces for many years will let you know what they will take...
 
My 1980 SRX is fixed and ready to go.IMG_1339.jpgNew Polaris clutch, new driven. I am going to give this a second chance. More traction products installed with aluminium skis. Should be fun.IMG_1337.jpg
 
What have you done to the stock secondary to allow it to work with the 1 3/8" belt?

In stock form they will not open far enough to allow full shift without stretching the belt when using an overdrive primary like a P-85.

If you have this problem you are severly overstressing your parts especially at the RPM you say your running. I think the 80 crank stub is also a little longer than the others to accomidate the oil pump drive which could give more leverage to the forces in play.

opsled
 
Driven Clutch

opsled said:
What have you done to the stock secondary to allow it to work with the 1 3/8" belt?

In stock form they will not open far enough to allow full shift without stretching the belt when using an overdrive primary like a P-85.

If you have this problem you are severely over stressing your parts especially at the RPM you say your running. I think the 80 crank stub is also a little longer than the others to accommodate the oil pump drive which could give more leverage to the forces in play.

opsled
Click to expand...
The driven clutch is machined to allow full shift. The crank broke shortly after taking off.
 
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