Hi every one, I hope your season is going better than mine so far. Alright I hope someone might be able to help here with this issue. I will start by saying I am the proud owner, well maybe I will rephrase that and say I am the owner of 4 VK540's, 1-2003, 1-2005 & 2-2008's. Each one of them has a blown mag side piston?? The 2003 has just gone through its second piston tonight. So that brings the total to 5 mag side pistons in 4 different motors. What up with that! I could understand maybe if it was a lean run and a burn down holed piston but it isn't that, all of them, all 5 have dropped their skirts. Anyone else having troubles with these motors in this respect. Is this a crank problem right from the factory? Maybe clutch issues throwing a weird harmonic into the crank that makes the far side piston drop it's skirt? Any input? Any ideas of what I should do to try and cure this?
yamahamark
Member
Sounds like it might be a factory problem.
A couple of bucks
VIP Member
Not a chance. Was all gas bought at the same station?
grasshopper
New member
Do all have a crank seal leak? Perform a leak down test.
I had bought 3 of them for parts already blown on the mag side, complete machines just bad motors. Another of them went early this year I rebuilt this motor with new crank seals and all new gaskets again it has a bad piston, all mag side pistons all of them with no skirt, and one was a factory Yamaha motor with only 2600km on it. All gas was from the same station just at different times and years, it is the only gas distributor within 150km from us so we have no choice. I will say that 3 of the motors did have over
10 000km on them when they finally did go. But again why all mag sides never the pto. I am thinking on sending one of the cranks out to get rebuilt and welded rather than going with a new Yamaha crank. I think that possibly a backfire is throwing the phase of the crank out just that little bit and this is making a funny vib in the crank and it is beating the skirt right off the mag side piston. Going back to the gas I did read an article about water in gas going through the carb and then for some reason making the skirt come off a piston, but I would have thought at some point in time this would have affected the pto piston as well not just the mag side especially due to it being a twin cylinder single carb motor.
10 000km on them when they finally did go. But again why all mag sides never the pto. I am thinking on sending one of the cranks out to get rebuilt and welded rather than going with a new Yamaha crank. I think that possibly a backfire is throwing the phase of the crank out just that little bit and this is making a funny vib in the crank and it is beating the skirt right off the mag side piston. Going back to the gas I did read an article about water in gas going through the carb and then for some reason making the skirt come off a piston, but I would have thought at some point in time this would have affected the pto piston as well not just the mag side especially due to it being a twin cylinder single carb motor.
Yamaha Nutz
New member
you must have a air leak some where ...but then again you said the skirts are breaking off so that would tell me you have too much piston clearance and the pistons are slapping hard .....i find it very hard to believe that the crank is out of phase as the pins are all splined and the center if is either splined or keyed and very hard to twist .....in all my years i have found crank seals, base gaskets, or sloppy piston clearance to be the cause to these engines going down
Thanks for pointing the splined crank out Yamaha Nutz, so I guess we will throw my thought of crank twist out. What you are saying about piston slap and too large a bore makes somewhat sense. But I will tell you what I did earlier this year to patch the blown motor. I took two motors both with blown mag side pistons and built one swapping the good pto piston and cylinder from one of the spare motors onto the other motor after completely disassembling, cleaning and putting back together with all new seals and gaskets. And again the mag side piston is shot. So it very well could be worn piston and bore but again always mag side?? Oh well it is what it is and it will be rebuilt asap. Going back to the splined crank halves that should make it very much easier to rebuild, have you done one of these. I have done a single cylinder crank in my flat track days but I have never attempted a twin due to the fact of getting everything buggered up on the reassembly. With these cranks being splined it will take a lot of the measurements out of the equation and be much more simpler on reassembly no? Any input or things I have too look out for when rebuilding one of these cranks, or should I just send it out.
Another thing I thought about is the pulse line is pulled from the mag side cylinder. I thought maybe this could be causing a problem but it would cause a lean condition if it were leaking and a melt down no not a dropped skirt. Plus everything "looks" ok on the lines and pump.
Yamaha Nutz
New member
it has been a while since i have done a SRV crank and i can't remember if it is keyed or splinned ...but it is either or .... i do a bunch of GPX SRX and Phazers every year
while it seems straight forward and does make things easier you can still screw things up easy if you don't know what you are doing or if you have to replace a rod pin hardest thing i deal with is obsolete parts for these cranks ....just have to spend time figuring out what else will work with in the last month we have lost a few more oem parts so sourcing from the aftermarket is the only option .....SRV cranks are pretty stout and can take a beating the last one i did had a bent rod from hydo locking even before i took it apart i checked the deflection and it was still straight even with the bent rod that much i remember
while it seems straight forward and does make things easier you can still screw things up easy if you don't know what you are doing or if you have to replace a rod pin hardest thing i deal with is obsolete parts for these cranks ....just have to spend time figuring out what else will work with in the last month we have lost a few more oem parts so sourcing from the aftermarket is the only option .....SRV cranks are pretty stout and can take a beating the last one i did had a bent rod from hydo locking even before i took it apart i checked the deflection and it was still straight even with the bent rod that much i remember
RON HYDRAULIC YAM
Member
I bought a 93 VK used a few years back just to make cross country ski tracks ,,, It ran decent but wouldn't idle ... Finally one Sat morning I
decide to pull out the plugs and PTO was packed w almn ... I had heard the skirts come off the year before and had just brushed under some ice
coated branches and thought it was ice hitting the fan ,,,.. The skirts were packed in the ports , 3/16 groove in wall from piston pin , Almn packed
into the crank brgs .. Tough beast had put on at least 262km with no outer crank seal and the plug to seal off the gears to inject pump
was missing from sled ... the Mag side had been on fire and partially melted .... Some one had used ether at some point before I got it...
Rebuild from an SR540 ? engine with bigger reed cages from the btm up and runs much better ....
Surprised that they might blow up with no good reason ...
Hope some of the other ideas sort them out..
Ron
decide to pull out the plugs and PTO was packed w almn ... I had heard the skirts come off the year before and had just brushed under some ice
coated branches and thought it was ice hitting the fan ,,,.. The skirts were packed in the ports , 3/16 groove in wall from piston pin , Almn packed
into the crank brgs .. Tough beast had put on at least 262km with no outer crank seal and the plug to seal off the gears to inject pump
was missing from sled ... the Mag side had been on fire and partially melted .... Some one had used ether at some point before I got it...
Rebuild from an SR540 ? engine with bigger reed cages from the btm up and runs much better ....
Surprised that they might blow up with no good reason ...
Hope some of the other ideas sort them out..
Ron
low slung
Member
Heard the older phazer motors(485)would snap off shaft(or crank)on the fan side and meltdown.Is the 540 a similar design?
Throttle Junkie35
New member
If the crank snaped off on the fan side....it would not run. I've seen failures of the fan it self (bascially the blades break off) on both motors. more so on the 540.
low slung
Member
My old mans ET410II has a axial driven fan,but the phazer 485 and VK540 motor were belt driven fans(weak or broken belt=meltdown).
Throttle Junkie35
New member
Yep, that would do it too. The Et410 etc.. have what you would call a radial fan. The 485 and 540 are an axial fan.
low slung
Member
My mistake,still thinking back to the 1992 brochue(V-max4 on the cover)with these specs.Always thought the VK540 motor was bulletproof(is in these parts)?
82f100swb
New member
I just did pistons in my 86 SRV, had it out to change the oil pump cable, and found a very worn and cracked mag side skirt. The PTO side had some wear not unexpected for 6100km.
The sled had came with a parts engine from a VK. You guessed it, it has a cracked mag side skirt.
Sent from my SM-G900W8 using Tapatalk
The sled had came with a parts engine from a VK. You guessed it, it has a cracked mag side skirt.
Sent from my SM-G900W8 using Tapatalk