Spun crank or bearings?

S

sevenspeed

New member
I am still on my search for a clean Vmax4. Today I had to drive some distance for work and was passing a '96 I found on CL. Headed out with my empty trailer...

On arrival the seller tells me the #1 cylinder [plug] has made contact with the piston. Verified visually -- mark on the piston.

Seller reported that the sled started backfiring last ride out. I want to hope for a bearing here, but really feel this is a spun crank. I am driving back past this machine tomorrow and must make a decision. Mostly considering making an offer on the machine as-is, and then rebuilding this to my liking.

How far off am I on my guess? Told this one has a 95 engine due to a rod thru #4 in the past.

Cost to rebuild this PROPERLY without cutting corners?

Thanks everyone.
 
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I HIGHLY doubt the crank spun on that 800 engine..I`m not sure i have ever heard if it happening on an 800..

not sure what you mean by the "cylinder" made contact with the piston, did you mean the "head" made contact?

if the top of the piston apears to have little indentations, that`s likely the result of a burnt down piston, and the debri got caught on top of the piston, and pounded the head...

cost would be imposible to guess with the information provided?
 
Oh geez. I did not read what I typed.

#1 piston made contact with the spark plug electrode. Electrode bent, mark on the piston.
 
Is it even possible for a piston to hit the electrode before it hits the head???

Seems it should also contact the head at the perimeter????

Foreign object??

opsled
 
+1 on what Phill said, don't think its possible for piston contact that.....

The Viper I bought that lean burned down had a crushed electrode. It was piston ring fragments that caused it.


M
 
Ok... I was wrong. You guys were right. When I looked at the sled I had 5 minutes to drop my empty trailer and head off to work. The following day I came back and was able to spend time with the machine. No time needed; everything was there to see: #1 piston experienced nasty lean burn and eroded the piston down to the top ring landing. Piece of ring missing. Piece of the JUG was missing at the intake port. The indentations all through the head matched the profile of the missing piece. #2 looked slightly rounded on the exhaust side piston edge. This you might tolerate for the rest of the season if it was the only problem with the sled.

If you were in my position, would you stop there? Nope. #3 at 120PSI. Oh, ok! #4 at 60PSI. Oh geez... removed the other head to inspect. #3 similar to #2. #4 has a quarter sized erosion in the center of the piston and erosion on the piston edges that is just making contact with the ring. Full rebuild required here.

I made an offer on the machine that reflected this damage. Owner was in denial. "But how would any of that metal make it below the pistons?" I was explaining that engine would require full disassembly, careful inspection, and rebuild. He was convinced he could slap on a jug or two he had lying around (oh geez I hope the boderline pistons are not re-used!). The awful conclusion of this is that owner reported the machine was running a bit "off", made plenty of power, but was backfiring greatly.

I know it is said here over and over, but when something feels off: it IS off. If you think you hear a new strange noise or notice your ESP like connection to the engine feels different: something IS wrong. It's so tempting to just go on and enjoy the ride. This goes for anything with an engine... that trailer full of snowmobiles you are towing... you get it. This owner could have prevented this with a carb cleaning. "it has not been serviced in two years". Such a shame.

Ummm... so I bought another one just 14 miles away, this one is home, and this one RUNS! Now I am off to work in the freezing rain that is falling to clean up the clutch on the new one. Looks ignored and I expect big changes in the next hour.

And a HUGE thanks to roadrunner. Do you know what an amazing asset you have in your community? This gentleman saw the post here and by email #3 had sent a comprehensive list of every vmax4 for sale within 2 hours of my location. He even contacted owners for me. Amazing! Here is a person that has true passion for this machine. Awesome!

THANK YOU EVERYONE!!!
 
I can totally relate!!!!

this sounds like the guy i got my sled from exactly!!

the guy fired it up..sounded HORRIBLE, was poping etc..he rips it around the yard (or should I say LIMPED it around the yard)..he pulls back up, I told him go ahead and shut it down, and said yeah something defiantly does`nt sound right..i did`nt know jack about a vmax 4, other then it`s a two stroke, and defiantly sounded BAD..LOL

anyway, the guy says cylinder one is a little low on compression, so i think it`s just a stuck ring, but it`ll still easily go 70mph or so..LOL.

long story short..I got it, had TWO comepletly burnt down pistons!!
I already figured there was some problems, and i was going to be pulling the motor..but the price I paid for it, I was still happy..

the guy wanted $1000 for it (1995 800), well, a little while before this, I had purchased an ole honda cb 750 (1975? i think it was)..anyway, i got the bike for $200, put about $50 in it...the owner of the sled happen to mention he was looking for a bike for his ole lady, so i mentioned i had the perfect bike..he ask how much i wanted for the bike, i said $800..so i gave him the bike, and $200..so in totall, i had about $450 into the sled...of course i had to rebuild the motor..but it still worked out to be a good price in the end i think...two cylinders replated, two new pistons, and a gasket kit...and a few other things here and there..various suspension bearings etc..
 
The sad part is that I am now 4 hours away from that sled, but it is still calling me. It wants to be rescued and rebuilt. Going outside to play with the one that I brought home instead..
 
sevenspeed - Thanks for the compliment. Don't forget, I am only an hour away from the sled and I would have no problem picking it up for you and keeping it here, until you could pick it up.
Have fun on your new VMax-4!
 
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