help with a R1 motor

[RaWarrior]

Or specifically, the engine in my Yamaha RX-series snowmobile. The "genesis extreme", or a tweaked/tuned for snow R1 engine. 1000cc I4, quad carbs. Motor is all stock except for muffler(equivalent of slip-ons to a bike).

Anyway, I was out riding today and got onto a lake. Absolute perfect conditions to really haul ass....just a little hard-packed snow to get good traction but not so much as to "drag" on the skis. To the bar, spins up to it's usual 10k rpm or so and slowly fades down to about 9300 as the clutches backshift into the highest ratio, which is about 110-115mph. Hold that for maybe 30 seconds. Ease up for a "corner" on the lake down to 70 or so, then back on it. Once it cracks 100 or so, there's a quiet(but audible over wind/motor noise) whap-whap-whap-whap under the hood. I ease off and it goes away, everything still seems to be working normally. I bring the speed up again but hold off WOT, running at maybe 70 or so. Motor seems....different. When you're "rolling on" the throttle, it feels like it drops a cylinder, once throttle position is "steady", it comes back. Power still seems to be all there, idle is fine and starts easy as always, but it's got a definite "fartiness" to the motor....a definite lag on the throttle. At the next stop I realize the "whap whap whap" was the belt disintegrating and flinging pieces of itself all over the engine compartment. Swapped in the spare belt and continued the ride.

The rest of the day it drove okay, but noticeably different. The engine noise at idle is slightly different. My buddy I was riding with didn't notice, but I've been on this sled long enough that I picked up the idle didn't sound quite right. A faint knocking was mixed in that sped up with engine speed. Also, it drove totally different. I swear the motor felt considerably more powerful. Even maybe 1/2 throttle would send the revs up to 11k+ and absolutely launch the sled. Nailing it from a standstill resulted in the motor bouncing off the rev limiter at 11,500(which it's never, ever touched before). It really seemed like a peppier, more powerful motor. Except it would sometimes(but not always) drop a cylinder on acceleration and had that noticeable knocking noise.

Coolant temp never went above normal(160* or so), oil level is fine and it didn't start burning any, and no check engine light on the dash(though it's carbureted so there's not a whole lot of things the CEL can actually detect)

I'm sure the jaunt at WOT on the lake caused this, so any ideas what actually went wrong in there? I initially thought it might have burnt a valve, I'll probably try to check compression in all the cylinders sometime this week. Any other ideas? What lets go on a Yamaha I4 from running it too hard?

 

[The Beekeeper]

Check the plugs when you do the comp test, they could indicate an overly rich/lean condition or potential combustion chamber issue, is the ignition timing controlled by the computer?

 

[RaWarrior]

Yeah, it's all computerized. Uses COPs like a modern sportbike engine. From what I've heard, it uses a preprogrammed 3d map to adjust timing based on ambient temperature and elevation in respect to rpm.

The FI motors can be adjusted for fueling right through the handlebar controls...each injector can individually be adjusted from -10(lean) to +10(rich), with 0 being stock. Mine has a TPS as well as individually controlled bowl temp sensors/heaters. Hot engine coolant also flows in jackets around the slides/throttle plates to keep them from icing up with snowdust.

 

[06VMAXIMUS]

Is it possible when the belt disentegrated, it screwed something up in the clutch (es)?

 

[acammer]

Check the plugs when you do the comp test, they could indicate an overly rich/lean condition or potential combustion chamber issue, is the ignition timing controlled by the computer?

+1 on starting with a quick plug read - leaned out or oil will tell you plenty. Audible knocking sounds like a pretty big problem, I'd also take a look in the oil to see if there is any evidence of metal shavings.

As for the increased performance, when you changed the belt perhaps you've got the clutches acting different, and that's what you're noticing. I suppose its also possible something occured when you wrecked the other belt that something in the clutches got messed up which is affecting the way the clutches perform, and could even be causing your knocking noise.

However, if it feels like its putting a cylinder down at times, and is knocking, I think you've got problems in the motor. Its a little weird that its intermittent, maybe valvetrain related, if you hurt the bottom end I'd think it wouldn't have tolerated bumping the limiter at 11.5k rpm after the fact.

Keep us posted.

 

[RaWarrior]

OK, went out today and gave it a closer look. The high-revving issue was because the helix inside the secondary had partially disintegrated, the upper points of the three towers were all sheared off on both the helix and moveable sheave side. So the clutch is toast. It opened too far and let the belt go too far down which started ripping it apart. That all makes sense so far.

Checked compression. Across the 4 cylinders I got 170, 150, 170 and 160. The manual says "normal" is 205 and "minimum" is 180. So they're low, but they're low across the board. All the plugs looked perfectly fine, a dusty brown color.

With the hood up and listening closely with the motor running, there's a definite knock coming from the head of the motor. If you touch the valve cover you can even faintly feel it. When you rev it up a bit, the knock is mostly lost in engine noise, however, holding it at say, 4000RPM or so, randomly and for a split second, the knock gets suddenly louder and when that happens it definitely loses a cylinder, can instantly tell in the exhaust noise.

What could be knocking in the head? A loose camshaft carrier allowing the cam to slip around a bit?

 

[The Beekeeper]

Try a wet comp test, squirt a little oil in each cyl and retest compression, this will help tell if the rings are sealing well or if your losing compression past the valve seats or gaskets, I would pull the valve cover and look for loose valve train components in the case of the knock, another possibility would be somthing got pulled into the cyl and is lodged in the piston or combustion chamber, I have seen excessive carbon deposits cause a knock before but I doubt this would be the case here, thanks for keeping us updated..................

 

[tugla]

i was going to say check the clutches, might need a cleaning and chg of parts besides what you found messed up. hopefully nothing in the primary messed up the balance of the motor. sorry im not back in the yukon im pretty good friends with the yamaha guys and they know lots about these motors as all the guys working there are racers and moders.

what year sled is it?

 

[maxcruiser]

I agree with Beekeeper, try a wet comp test, will help pinpoint valves or rings problem. I would than take the valve cover off to inspect cam lobes, valves springs, etc... Than you turn the engine over by spinning the primary clutch.

I owned an RX-1 a few years ago, great sled. It was the first model year, only issue I had was with the back to front weight transfer on sudden deceleration.
The front end would go into a kind of speed wobble/tank slapper after shouting down after a high speed run on the lake. Fix that with some rear suspension upgrades.

Mike

 

[acammer]

OK, went out today and gave it a closer look. The high-revving issue was because the helix inside the secondary had partially disintegrated, the upper points of the three towers were all sheared off on both the helix and moveable sheave side. So the clutch is toast. It opened too far and let the belt go too far down which started ripping it apart. That all makes sense so far.

Checked compression. Across the 4 cylinders I got 170, 150, 170 and 160. The manual says "normal" is 205 and "minimum" is 180. So they're low, but they're low across the board. All the plugs looked perfectly fine, a dusty brown color.

With the hood up and listening closely with the motor running, there's a definite knock coming from the head of the motor. If you touch the valve cover you can even faintly feel it. When you rev it up a bit, the knock is mostly lost in engine noise, however, holding it at say, 4000RPM or so, randomly and for a split second, the knock gets suddenly louder and when that happens it definitely loses a cylinder, can instantly tell in the exhaust noise.

What could be knocking in the head? A loose camshaft carrier allowing the cam to slip around a bit?

Between the knocking, low compression, and intermittent cylinder dropping, I think you might as well go ahead and pull the head - clearly something is amiss and you could be risking some real damage if what-ever valve is malfunctioning ends up making contact with the piston.

 

[RaWarrior]

The front end would go into a kind of speed wobble/tank slapper after shouting down after a high speed run on the lake. Fix that with some rear suspension upgrades.

Mike

Mine does that too, it's the last of the RX's, and 05. In 06 the Apex came out. Even letting off the gas results in the front end getting kind of squirrely. I blame it on the garbage stock skis that dart all over the place but I've been too cheap to replace them and I've just come to expect it. I've fiddled with the rear suspension endlessly and never found a setting I liked. It's harsh over small bumps and cases flat on big ones. It's just too clumsy of a sled for how I ride. The seat is too low, the handlebars aren't tall enough (and I'm only 5'8), it's too heavy, and the suspension blows. The engine was the high point, and it just took a dump on me with only 5500miles.

The season is almost over anyway (another few weeks tops around me), so I'm just going to bring it home and park it. If I get time between work and Vmaxing around this summer I might tear into it, if not, I'll sell it as-is and take a hit on the value.