Center cylinder lost all compression - your guess?

S

Sidekrans

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Feb 8, 2016
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Hi,

First post for me. I've recently bought an abused viper mtn 04. The condition wasn't exactly great but the prices was so..

20170226_164506.jpg

Anyhow, I've noticed the performance going done for a couple of days now. I started to notice this at the same time as I changed the drive-belt so I thought it had something to do with that at first.
On my last run here in the northern Sweden the performance suddenly dropped over a lake run, I could also hear something wasn't right and it had some "exhaust-poffs" at idle also.
I've been really gentle on the thumb because of the new drive belt so I haven't been pushing it.
Back home a did a compression check and found the previous high reading of a 132 now was below 50 for the center cylinder. The other ones were still at pre-season levels of 120 and 132.

Because of its condition I have a long TODO-list and have taken care of some of the more serious like chassi cracks, new seat and cooling system leakage but I haven't done the cleaning of the valves.
So I checked the condition of the valves today and they were a mess. The center was completely stuck. The other two were also in real bad condition. I finally got the center out and it too looked awful but it also had additional damage to it.

20170313_131521.jpg

Re-installed the valves and I thought it sounded happier now.
Did a new compression test and reading was the same on the center.

I'm ready to order a set of new pistons and do a complete rebuild.
Looking at Wiseco right now, would like to go OEM but the price is almost what I gave for the sled so...
The mileage are over 9000km or close to 15000 miles and no clue when last rebuild was done, if any.

Where I'm at I have no access to a garage right now so I cannot open it and see for myself so can only guess what's happen.
What is the most likely cause of the compression drop to your ears, piston, rings, gasket, something I'm missing?
Could the stuck valve be part of the reason for the failure you think?

Anything else I should do at the same if doing the rebuild?
 
Looks to me like valve went in too far and was hit by piston. Possibly not adjusted correctly and or lack of maintenance.
 
Yeah, there's no question there. The piston took the powervalve and it's a mess in there. You probably need a new cylinder too, and to flush the crankcase as well.
 
Sidekrans said:
Hi,

First post for me. I've recently bought an abused viper mtn 04. The condition wasn't exactly great but the prices was so..

View attachment 63024

Anyhow, I've noticed the performance going done for a couple of days now. I started to notice this at the same time as I changed the drive-belt so I thought it had something to do with that at first.
On my last run here in the northern Sweden the performance suddenly dropped over a lake run, I could also hear something wasn't right and it had some "exhaust-poffs" at idle also.
I've been really gentle on the thumb because of the new drive belt so I haven't been pushing it.
Back home a did a compression check and found the previous high reading of a 132 now was below 50 for the center cylinder. The other ones were still at pre-season levels of 120 and 132.

Because of its condition I have a long TODO-list and have taken care of some of the more serious like chassi cracks, new seat and cooling system leakage but I haven't done the cleaning of the valves.
So I checked the condition of the valves today and they were a mess. The center was completely stuck. The other two were also in real bad condition. I finally got the center out and it too looked awful but it also had additional damage to it.

View attachment 63023

Re-installed the valves and I thought it sounded happier now.
Did a new compression test and reading was the same on the center.

I'm ready to order a set of new pistons and do a complete rebuild.
Looking at Wiseco right now, would like to go OEM but the price is almost what I gave for the sled so...
The mileage are over 9000km or close to 15000 miles and no clue when last rebuild was done, if any.

Where I'm at I have no access to a garage right now so I cannot open it and see for myself so can only guess what's happen.
What is the most likely cause of the compression drop to your ears, piston, rings, gasket, something I'm missing?
Could the stuck valve be part of the reason for the failure you think?

Anything else I should do at the same if doing the rebuild?
Click to expand...


I wouldn't go with wiseco pistons, you'll have a much greater chance of a cold seizure. If you don't want to go with OEM pistons I'd use SPI.
 
Kramer660r said:
Looks to me like valve went in too far and was hit by piston. Possibly not adjusted correctly and or lack of maintenance.
Click to expand...

norwegian said:
Yeah, there's no question there. The piston took the powervalve and it's a mess in there. You probably need a new cylinder too, and to flush the crankcase as well.
Click to expand...

I guess you're right. I was hoping for some other answer though.
I have to go out and open up the top now to see for myself...
 
shaggyzr2 said:
I wouldn't go with wiseco pistons, you'll have a much greater chance of a cold seizure. If you don't want to go with OEM pistons I'd use SPI.
Click to expand...

Ok, noted, Wiseco is out.

Since the Yamaha dealers in Sweden have ridiculous prices on pistons/rings I'm left to buy overseas like boats.net. Too bad the import charges are quite high.
If anyone can recommend an OEM seller with good prices on piston/rings I'm all ears.
I will keep this sled "forever" so I would like to do it right, but not at any cost.

The valve should probably be replaced or what do you say?
 
So I went out today (in the snow fall) and took off the top and exhaust.

piston_top.jpg
cyl.jpg
piston1.jpg

So I'll start looking for a used cylinder, valve, 3 new SPI or OEM pistons with rings, a gasket kit. Anything else I should shop?
 
I did not think the valve is able to reach the piston. Is it possible the valves were installed upside-down?

Sent from my SGH-I337M using Tapatalk
 
Sidekrans said:
Ok so you don't think the poorly maintained valve (lots of crap on them) was the cause of this?
Click to expand...

no its was not ......ask don he got alots of experience with viper ...u should take picture of the other top piston to see if we see some wash on top .....don will chime up
 
modsrx said:
no its was not ......ask don he got alots of experience with viper ...u should take picture of the other top piston to see if we see some wash on top .....don will chime up
Click to expand...

Here's a video:
https://drive.google.com/open?id=0B2-jDnAzUDk8ejR1Vm5fQWR1MDg

I'd like to hear what you think about the condition. I know it's dirty and all, the Viper is in for a real make-over soon...

I've ordered full gasket set with crank seals, three new pistons and rings with clips, bearings etc.
I've found a used valve and will order it along with a thermo sensor that was broken and an air intake box to replaace mine that was in bad condition.
Also found a used cylinder that might buy that as well if this one is beyond hope.
 
Sidekrans said:
Ok, noted, Wiseco is out.

Since the Yamaha dealers in Sweden have ridiculous prices on pistons/rings I'm left to buy overseas like boats.net. Too bad the import charges are quite high.
If anyone can recommend an OEM seller with good prices on piston/rings I'm all ears.
I will keep this sled "forever" so I would like to do it right, but not at any cost.

snip/QUOTE]

As long as you understand that a Wiseco piston's thermal expansion rate is different than an OEM or other cast piston brands and adjust your warm-up routine accordingly, you won't have issues provided you follow Wiseco's recommended clearances when installing.

Be the first to start your sled and suit up outside while everyone else is inside dressing. Light throttle for the first few miles (distance dependent on cold soak time).

It's a quality piston but not for the - pull the cord and flipper to the bar - kind of trail rider which is why most folks recommend against using it. Something to consider if the OEMs are so much higher in cost and you aren't the hasty type.
Click to expand...
 
snomofo said:
As long as you understand that a Wiseco piston's thermal expansion rate is different than an OEM or other cast piston brands and adjust your warm-up routine accordingly, you won't have issues provided you follow Wiseco's recommended clearances when installing.

Be the first to start your sled and suit up outside while everyone else is inside dressing. Light throttle for the first few miles (distance dependent on cold soak time).

It's a quality piston but not for the - pull the cord and flipper to the bar - kind of trail rider which is why most folks recommend against using it. Something to consider if the OEMs are so much higher in cost and you aren't the hasty type.
Click to expand...


I heard the warm up was essential. I wouldn't be comfortable lending the sled to friends and family with such restraints on usage. After advice in this thread I ended up with SPI pistons instead.

I'm about to place an order on a used cylinder now - a new layer of nicasil (I suppose that's what's needed right?) will cost me about $230, the used cylinder I'm looking at is less than $80.
 
Last edited:
A short update.

I've replaced everything mentioned above, new cylinder, all pistons, welded cracked exhaust, new air intake box, new valve, new temp sensor etc.

The sled fired up but sounds like it was running on only two cylinders. Compression good and back to normal, sparks ok.
Started up again and let it run on half choke - all three cylinders running now.

I'm guessing there is something with the gas/air. Probably a dirty carburator. Will dig into it next weekend.

In a way I'm glad I finally found something that could explain the melted piston.
Even though the exhaust had cracks and the exhaust donut was in bad shape due to a couple of springs missing I just wouldn't believe that to be the cause.
 
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