Vmax ST blown up twice

C

Chris

New member
Hey guys i baught a 1994 V Max and the dealer ship sold it to me blown up so they rebuilt it on there cost wich was nice but it blew up again with only 30 km on it , it keeps melting a hole in the piston , so i braught it back and they said it was out of time and it was a 180 crank in it . Is it posible for them to tell this with not even taking the heads off ? i didnt think so but they said it was. So there ordering me a crank and piston and all seals , Now if it was a 180 degree crank is thereany specs for i can get this done at a shop with the new crank ? and is there a way for me to tell if it is a 180 crank by the CDI ? it appers to be stock , stock coils and such , also looking for all the torque specs adn sequences to rebuild it down to the crank . Any help would be great thanks guys
 

Yes, you can tell if its a 180 crank without removing the heads...just pull the plugs, and see if two pistons come up to TDC at the same time..a 180`d crank, means TWO pistons, always travel together...so it basicaly makes it a big twin..LOL
Look to see 9roll the motor as needed) anyway, look to see, if you can get two pistons, to be at the top at the same time...
other wise, a regular 90 degree motor, will only have one piston at top, at a time..

also, you should be able to tell by the cdi...there`s another post on here by a guy named fastmax i believe it was, that has the info on that..

As far as a hole in the piston, I`d "gues" thats more likely a dirty carb, or a leaking crank seal..

specs on a 180 crank, is only a matter of how you line up the pre factory marked crank halves...each crank half, will have a dot on the gear..line the dots up for a regular 90 degree motor...for a 180 motor, you off set the dots at a certain degree..
180 crank, and a regular stock 90 degree crank, is the same exact thing...just has the gears lined up differantly..

Search this site, and you`ll find a complete manual, with all the specs you`ll ever need..

ohh, and welcome to vmax4.com!!

AL P
 
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Thanks . I was guesing a leeking crank seal too but the dealer ship didnt believe me , They did it at there cost so it was as cheep as posible . so they did a carb cleaning , base and head gaskets and didnt even check the crank seal , They wanted to give me my money back so im assumeing they didnt even check the crank they said they didnt take it apart or any thing but they knew the crank was out . . . . Highly doubt full so i talked to them and and insted of getting my money back i got them to supply a crank , all seals and gaskets needed for a rebuild so thats my next project. Its most likely just a crank seal but if there offering a crank , berrings ,conecting rods , and seals i might as well do it all
 
So now there only giving me a half crank . jus the one side , Where do these cranks normaly twist right in the middle ? will i be ok to change jus one and not the other when i find out witch is twisted ?ill still have to change seals on the one side , am i better to get the whole thing ?
 
Yeah each crank half has a large gear on center of the motor end of the crank, half....
usually one of these gears will slip, when that happens, it throws one crank half out of time with the other (and of course the ignition timming will be off also)..
have they checked both crank halves, and concluded that the gear on one of the crank halves has defiantly slipped (twisted if you will)?..
 
So i got her all apart , Should bothe the cranks have like the same twist ? like the stoke at the same time , , , , if you know what i mean , it is not a 180 crank , but i took them apart and put them next to each other and the one has a little but differnt of a twist i think , I put them together with the other dots and made it a 180 and moved it and the one comes to TDC befor the other ? is that a spun crank ?
 
In stock form..90 degree`s..no two pistons, would ever be at TDC at the same time...their would always be 90 degree`s (1/4 of a turn) of crank rotation, before another piston reached TDC..

looking at the crank..as if you were setting on the sled...line up the gears, however it takes, to get the crank/pistons to be in the postision picture in my link below..
if you can get the pistons positioned like pictured...then see if the dots on the gears are lined up...even if they are...it could still be out by just a few degree`s, which would be very hard to see....but this may give you an idea..

this pic, is what a stock 90 degree motor would be at..

http://img705.imageshack.us/img705/2017/crankrotationvmax4.png
 
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So the Dealership looked at it and said it was out , , , how they checked with a hole in the piston and the heads still on i do not to know so i braught it in and getting it rebuilt , They sent it away to a place in quebec , and supposably if theres any damage there going to weld it , and put new seals and berrings , If they dont weld it do you jus put a tack of weld on it ?
 
No I really would`nt say they tack weld it...more like a solid good weld all the way around the gear where it meets the crank half..
 
So the dealer ship got my crank back from Quebec where they supposivly "pinned" the crank , is this a good idea ? Now is that the most likely cause if all the seals and carb was good for it "holing " a piston ? It was #2 from pull cord side ,
Is there any quick easy ways to gain some performance ? Clutching Ect. . .
 
not sure i understand what you/they mean by "pinned" the crank???, that does`nt sound like welding, or "key way"`ing it to me??

also, I`m not to sure a twisted crank would hole a piston??..if the crank did twist...two pistons would be off, not just one, so why only one piston damaged??

can you go see the crank? if so, can you take a couple pics, where the large center gears are on the crank halfs?
also, something to check, is the pulser line on the number two from pull cord side...under that cylinder, is a hose running off the crank case, and going to one of the fuel pumps..if that hose, is loose, or split etc..it`ll suck air, and burn down that cylinder..that`s what happened to mine...also happen on my number one cylinder (nearest the clutch)..that cylinder also has a hose running off the crank case under it..that one on mine was split...

here`s a pic of where they`d weld it..
copyofvmax4crank.jpg


AL P
 
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The pinning, i was told, is the Yamaha recommended method, and what the local dealship here did in the day. if you look between the gears and seal you will see the gear has a shoulder, they drill through,pin and weld it.

This is how Mongoose Enginnering do it, its not cheap, around $500 bucks a side plus shop fees................ So they are not scrimping there.
 
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after all of this i got it back together last year and had a blast with my 4 all winter looking forward to another winter with the vmax 4 pinning the crank seem to work very good
 
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