viper crank issues

S

ski-man

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I have a 02 viper in my shop with the center main bearings out, approx. 4000 miles. Not sure on what way to go, part it out or rebuild the crank or replace the crank. luckily the cases and all three cyls. escaped damage from the bearing failure. Anyhow, what's the deal with the crank problems on these motors, I have seen many of these sleds getting parted due to bad cranks and it seems that center bearings is a very common failure. I compared the viper crank to a 700 redhead crank (which seem bulletproof) and the bearings are larger all the way around in the viper. Any insight out there on why the issues with the vipers?
 

Its my understanding that the crank bearings are not the problem. The SRX actually has the same crank (minus the connecting rods). As we know the SRX does not suffer from the crank issues that the viper does. It's pretty much agreed on this forum that the problem is heat. A rear heat exchanger helps, but mostly the fact that the viper has a mono head, higher compression, more timing and a leaner setting from factory. All these cause alot of heat and heat ultimately leads to the failure of the center bearing. The Guru's on here recommend adding a rear heat exchanger, setting your carbs to a richer setting (3.25 or 3.5) and making sure your not using low grade gas. I have a viper with 9300 miles on it and no crank problems thus far. Just finished my entire engine rebuild just to be on the safe side.

Hope this helped.
 
02YamiSxViper said:
Its my understanding that the crank bearings are not the problem. The SRX actually has the same crank (minus the connecting rods). As we know the SRX does not suffer from the crank issues that the viper does. It's pretty much agreed on this forum that the problem is heat. A rear heat exchanger helps, but mostly the fact that the viper has a mono head, higher compression, more timing and a leaner setting from factory. All these cause alot of heat and heat ultimately leads to the failure of the center bearing. The Guru's on here recommend adding a rear heat exchanger, setting your carbs to a richer setting (3.25 or 3.5) and making sure your not using low grade gas. I have a viper with 9300 miles on it and no crank problems thus far. Just finished my entire engine rebuild just to be on the safe side.

Hope this helped.
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Spot on!Just want to add proper storage is KEY! A little rust/corosion on a SRX/Viper crank and WHAMO!
 
thanks for the replys, this viper does not have a rear heat exchanger, I have one off a 700 sx I could install or would one out of a srx be better?
 
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ski-man said:
thanks for the replys, this viper does not have a rear heat exchanger, I have one of a 700 sx I could install or would one out of a srx be better?
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The sx one will work but the srx one would be better, just bigger is all.
 
center and mag are usually the ones to go on the Viper for the reasons listed in post #2. I will add however that the SRX and Viper do not use the same crank. they are interchangeable but not the same. I'd have it rebuilt. since you're already in wisconsin do a search here on "midwest cranks" you'll find contact info for Jeff at midwest crank. very reputable. I've got a guy here that does mine for dirt cheap. cheaper than buying a used crank and I now what I've got.
 
heat is not what is killing the crank. It is either lack of oil or lack of proper storage. Now that these are older sleds, the lack of proper storage is adding up. People do not block off the outlet of the exhaust when storing. This leaves one cylinder open to atmosphere.
Heat on the problem bearings is a non issue. Think of what is right in front of those two cylinders on the case. The water pump housing. All that cold water is flowing over the front of the case. On vipers and srx sleds this water is somewhat a constant temperature as unlike a car, these sled us a mixing housing for thermostat. There is always water flowing around even when the stat is closed, when open, now you have hot water and new cold water mixing coming in, the more the stat opens, the more it closes off the hot water mixing port and goes to cold only water. Great system, quick warmup and no sudden influx of cold water to stress the motor.
The other part of the hot crank that doesn't add up is this. The motor is nothing more than a combination air pump and compressor. the compressor is on the top side and is where almost all of the heat is generated. the lower section (because this is a 2 stroke) is the pump part. All of the air, Cold, comes rushing into the engine with every rev. The first thing it hits is the top of the case, the crank and the rod. This is what keeps the crank and cases cooled the most and is why you don't see manufacturers wrapping a coolant port around the crank case. It is just not a big heat issue to start with. crank cases of 2 strokes are air cooled by their own cycles.
 
BETHEVIPER said:
heat is not what is killing the crank. It is either lack of oil or lack of proper storage. Now that these are older sleds, the lack of proper storage is adding up. People do not block off the outlet of the exhaust when storing. This leaves one cylinder open to atmosphere.
Heat on the problem bearings is a non issue. Think of what is right in front of those two cylinders on the case. The water pump housing. All that cold water is flowing over the front of the case. On vipers and srx sleds this water is somewhat a constant temperature as unlike a car, these sled us a mixing housing for thermostat. There is always water flowing around even when the stat is closed, when open, now you have hot water and new cold water mixing coming in, the more the stat opens, the more it closes off the hot water mixing port and goes to cold only water. Great system, quick warmup and no sudden influx of cold water to stress the motor.
The other part of the hot crank that doesn't add up is this. The motor is nothing more than a combination air pump and compressor. the compressor is on the top side and is where almost all of the heat is generated. the lower section (because this is a 2 stroke) is the pump part. All of the air, Cold, comes rushing into the engine with every rev. The first thing it hits is the top of the case, the crank and the rod. This is what keeps the crank and cases cooled the most and is why you don't see manufacturers wrapping a coolant port around the crank case. It is just not a big heat issue to start with. crank cases of 2 strokes are air cooled by their own cycles.
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I strongly agree as this has been my experience as well. Lack of oil "investigate the oiling system design" or moisture in storage "lots of ways to get moisture in there during the summer" are the likely culprits.

I wonder if others who tear into these engines could chime in also, especially those that see a lot of them.
 
I agree with 02yammiesxviper, "heat" IS the issue for the rod bearings going south in a viper and always has, no matter how rich you run the oilpump it will always be the center and mag piston that the rod bearings go bad in 99.99999% of every viper you find blown up, it will be 1 of those 2 cylinders down..guaranteed!
The actual culprit that causes the problems is....detonation, which comes from excessive HEAT. You have a recipe for disaster on a viper with the lousy pump gas these days.
Every single ingrediant below does 1 thing, they add heat, you add heat, and you get detotnation UNLESS you have enough octane to keep it sustained.

1.) increased compression ratio on center and mag cylinder
2.) increased ignition timing
3.) less water capacity and less cooling capacity with rear exchanger being a tube.
4.) mono head does not wick the heat away from the mag cylinder effectively
5.) lean carb settings on the needle and nozzles

Those 5 ingredients with todays lousy pumpgas and you get heat, which leads to detonation and you basicly "pound the rod bearings away". No amount of oil in the gas can keep this from happening, as its not a oiling problem, its a octane problem!
The reason the pto cylinder never blows up in a viper is the compression ratio is lower due to a larger/differnt combustion chamber spec. on the pto side of the viper head, so its not as sensative to the gas octane. The reason you dont see srxs down as much as vipers is the compression is lower and the timing is leess advance along with greater cooling capcity and the richer carb settings on the needles/nozzles.

Cranks are the same between the engines with exception to the pork chop style and the full circle crank, one isnt "weaker" then the other, same bearings. one crank style doesnt keep the problems from happening then the other does, its the 5 things listed above.

I have 5 viper cranks under the bench right needing repairs now from last winter, they all have 2 things in common, wanna guess?
 
I am getting the crank redone and I am installing a srx rear cooler. Recomending 91 premium non ethanol.

Would richening the needles be advised? How about cutting the squish on the 2 higher compression cyl's. to match the lower compression one done @ the factory?
 
Yes, I agree that detonation is very hard on bearings. Thus I stand corrected, indirectly "heat" can cause bearing failure. Good point Don.
 
ski-man said:
I am getting the crank redone and I am installing a srx rear cooler. Recomending 91 premium non ethanol.

Would richening the needles be advised? How about cutting the squish on the 2 higher compression cyl's. to match the lower compression one done @ the factory?
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Theres a ton of threads about moving the needles. As far as cutting squish you would have to add to it to lower comp, which would lower the PTO even more. Alot of guys swear by the opti-cool head gasket. Some have had bender head mod which evens compression out. With head mod you have to set that PTO carb like the center/mag cylinders. I have ben running multiple SRX's with 0 crank problems, just picked up an 04 viper S so I have ben reading up on the vipers lately.
 
snomofo said:
mrviper700 said:
I agree with 02yammiesxviper, "heat" IS the issue for the rod bearings going south in a viper and always has,snipQUOTE]


The OP complained of main bearings, not rod bearings.

Thoughts?
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you've got a point, he did say mains. I agreed with post #2 based more on rod bearings. I've next to never seen the mains the issue....
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I have a couple cranks sitting because of corrosion on rod pins. rods look fine, and the bearing on either side of the pump drives seem to be the ones that usually have to replace. I used to buy cores for parts but don't dare anymore.

Havent needed a crank in my 4 stroke.
 
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