Explosion in Viper Ville!

OldIron

OldIron

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I might be my own worst enemy!

I was trying to get three vipers started for the first time about two weeks ago. With the sun going down, the temps dropping and the wind annoying the heck out of me and my arms getting tired of pulling I started to resort to desparate measures. I started to pull plugs and give a little direct primming. Worked well to get two of the three vipers started. The third one was being stubborn so I kept doing this and it would run for a few seconds then die. Well, about the third iteration of this and "Bang!!" Every annimal in the area ducked for cover. The neighbor's 4th grade kid cupped his ears and keeled over like he had been shot! And my ears started to ring after I was first startled by the flame that kicked out somewhere near my shins. After convincing the neighbor's kid he hadn't been shot and that he was fine. And listening to him tell me that "That was like my dad's 30-06" over and over I got back to it. The viper fired up and I got her in the garage. By the way, the explosion dislodged the exhaust pipe from the can. When I got her started up I quickly noticed and corrected it.

I cleaned the carbs, did all my preventative maintenance and then took her for a spin this weekend. Right off I realized something wasn't right. It was running but seemed to be real sluggish. I couldn't lift the skiis, and it seemd to be boggish in the middle and on top. I checked the plugs and the Mag and Center plugs looked great. The PTO plug looked dark almost border line wet but mostly dark. I checked spark it was good. And for being out in the field we put a thumb over the spark plug hole and it had pressure. When I get a chance I'll check compression with a guage.

So I changed out the plugs and checked them later that day and it was the same deal. I know the cylinder in question was firing and I do believe it was running on all three but just that the cylinder in question wasn't producing what it should. I've never seen the symptoms of a messed up read or blown crank seal before.

My guess is I may have damaged a reed valve or blown a crank seal when I had that explosion in viper ville. The explosion happend prior to me cleaning out the carbs. Does anyone have any other ideas on this?

With a little luck maybe tomorrow I can take a better look at this.
 
Keeping in mind I have little to no personal experience with the viper BUT with this scenario on a SRX...basically the same....in theory. I would lean more towards a reed/carb problem than the crank seal. Usually when crank seals leak they go lean, what your describing sounds more of a rich/fouling problem. Easy enough to pull the reeds and give them a good look. Even if they all look okay maybe even swap them around and see if problem follows reed. If you run a compression keep in mind 1 cylinder should be less than the other 2, not sure which on your sled as they changed from PTO to mag or vice versa at some point over the years.
 
that was a good read...lol

check the reed block in that cylinder.........
 
Yes definitely check the carbs and all reeds. Reeds are known for issues on a Viper. And if you break part of a reed, you will loose your top end noticeably. Trust me, been there done that.
 
It think the fuel pump is fine since I drove around on it quite a bit. And I didn't have any symptoms indicating lack of fuel.

I'm thinking that it's the reeds. I just need it to warm up around here so I can get to it. It's been in the single digits and below recently. The good of it is that it's snowing here.

It's nice having three machines until it's time to clean carbs.

Thanks for all the good ideas. I'll post back once I can get into that machine and find out what happened.
 
Well, I thought it was going to be the reeds but I confirmed that they are good to go. Pulled the whole reed cage out and they looked brand new. And pretty much they are since they went in and only have two rides under their belt.

I also did the following: I did a compression test and the cylinder that looks rich was showing 10psi lower then the two good ones. Bad one being the #1 or PTO cylinder.

So with that info I was thinking that it may be a bad ring or rings. So I did a leakdown test on all cylinders when cold and when warmed up. The results were that all three cylinders were within 1% of each other when cold or warmed up. I put 90psi in and they all held at 87 to 86psi. According to the chart this is a 3% and 4% result respectively.

Still not sure why the compression test had a 10psi difference between the PTO cyl and the others.

I had already checked the powervalve and it's pretty wet due to the rich situation on the PTO cyl. However, no pull thru's and it seems to be working correctly.

One thing I did notice is that the carb T fitting was not connected to the air box. This is the fitting that connects the carb bank air lines to the air box. I was wondering if this could result in that PTO cylinder being rich while the other two seemed to be pretty much right on? It seems like they would all be affected.

I didn't notice a huge difference with the track lifted off the ground between the T fitting being plugged in and not plugged in (T fitting to airbox). I'm not sure if the T fitting issue is the cause.

I'm thinking about re-cleaning and adjusting the power valves. Then going thru that #1 (PTO) carb again.

Any suggestions/input is welcome.
 
viper has lower compression in pto from the factory due to the chamber in the head is larger so your engine is in good shape, it should read 10-12psi lower then the center and mag. (yamaha did this so you can use all the same main jets across instead of a stagger)

fitting left off the airbox would make it doggy and rich running, hook it back up and ride it......
 
I would check pv cables for pull thrue or broken cable. Great story btw. =)
Woops! Saw you already done that. Don's right, try it again with the fitting
back on.
 
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Unfortunately just connecting the t fitting to the air box didn't do the whole trick. It's still running with a bog most noticeably in the mid and on up.

So far:

Carbs cleaned
Throttle free play adjusted
Reed valves good
Power valves were cleaned and only about 80 miles on them since
Power valves adjusted last weekend- No pull thrus

Which brings me to a theory. After adjusting the power valves last weekend I lifted the back end and I ran the sled up to see if the valves were doing what they should. I noticed that when I started the machine the servo moved and moved back - I believe this to be normal. So I ran it up to 7500 (which I felt odd about) and I did not observe the servo move. I did this about 3 times. It never moved. So is it possible I have a CDI that is messed up? Should I pull one from the other machines and try the same thing? Or is this something I shouldn't even be doing?

I'm considering pulling the engine and checking everything over.
 
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I found a crankcase bold in the bottom of the engine compartment so I pulled the engine and I found two pistons that need replacing.

Some extra information:

On this sled I had pulled out the center gasket on my optical and I kept on smelling coolant whenever I had run it. Upon opening it up it seems like there was some coolant mixed in with the oil down in the crank case as in the picture. I don't believe that was me spilling in down there. Also, the bottom of the heads are very sticky, and two of the small end connecting rod bearings were sticky and hard to roll the bearings.

I'm just wondering if coolant can mess up the sides of a piston like these pictures?

My theory is this:

My optical mod was not smart and it was allowing coolant to get into the cylinder. Also with that bolt falling out (I didn't use thread lock because the manual didn't call for it there but I did torque everything to specs) this also allowed coolant to get into the crankcase. The bolt that fell out was on the mag side forward and it was the mag piston with the most damage followed by slight damage to the center.

I'm not sure if any of these would cause a bog but if after the engine rebuild it still bogs, I'm going to try swapping the CDI.

I'm glad I pulled this engine because I think this thing probably would have eaten itself apart.
 
Cant see the pics you speak of? Bolt that fell out? Head bolt? I havent heard anything about modifying opticool head gasket. Is it possible bolts were botoming out in cylinder and not torqueing head down to specs?
 
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roudyroy1 said:
why is the pto side cylinder lower compression? why dose this need to be done?
Click to expand...

they did this so you can run the main jets straight across all 3 cylinders. yamaha thinks the extra heat from the pto makes you need a bigger jet, all other srx from 2000-up all use a staggered jetting set up with the larger main on the pto. So by lowering the compression some it makes less heat so it reqires a smaller main jet........

total waste ot time for them to tool the head like that and how often does someone change the mains anyways....lol, I always thought it was stupid!
 
Sort-of-related question...

How do you keep the piston at TDC for a leak down test? I have an airplane and do that test regularly but need to have a friend hang onto the prop to keep the engine from turning since being even a few degrees off TDC will cause the engine to turn (real hard too).
 
Kenora said:
Sort-of-related question...

How do you keep the piston at TDC for a leak down test? I have an airplane and do that test regularly but need to have a friend hang onto the prop to keep the engine from turning since being even a few degrees off TDC will cause the engine to turn (real hard too).
Click to expand...

well the easy way on a snowmobile is to use a wooden dowel right thru the clutch against the frame or whatever. On your airplane or any engine where the spark plug goes in top of the head you could make a mechanical stop that would screw in the sparkplug hole and hold the other piston at BDC. say a 1/4" diameter rod welded to a old sparkplug base, of course this length of this would be custom fit to your engine application, but then its a 1 man operation to check.
 
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