Skorpion Tour engine rattle

[sandberg]

I have a Tour with 12k miles and when in third or fourth gear between 3k and 4k rpm, I get an engine rattle. Doesn't really happen in 1st or 2nd. Above 4k the engine is quiet. The bike otherwise runs fine. I am just worried that this is an indicator of a future problem and I am not able to do much troubleshooting myself. I would love to find a mechanic who can work on this but don't know where to find one anywhere near Atlanta. Any help out there would be appreciated!

[hb7]

Cked for enough oil ?......

[sandberg]

Yes, Checked the oil and even changed it. That is one of the things I can actually do.

[hb7]

Should be at least 2.5 qts of oil. Did you clean the oil return screen below the battery ? If that screen gets blocked, oil pump pick up is reduced and the cam tensioner might not tension the cam chain. If you have a real problem whatever metal is in that screen could be a clue...

Also inspect the cam through the valve adj holes for any obvious wear possibly caused by oil starvation.


OTOH, maybe you are hearing things ..

[Bill Jurgenson]

Did you clean the oil return screen below the battery ? If that screen gets blocked, oil pump pick up is reduced and the cam tensioner might not tension the cam chain.

hum. THe chain tensioner is automatic, but it is not hydraulic. It is a simple spring ratchet mechanism that couldn't care less if there is enuf oil in the engine or not. Not that it cannot cause problems - it can - but under normal usage and rpm range it is pretty foolproof. If you ever do have reason to remove the tensioner, be sure to lift the ratchet and set it back before reinstalling it.

If you have a real problem whatever metal is in that screen could be a clue...

Since that screen is in the line from the tank to the engine, you do indeed have real problems if there is anything metallic in it!

Also inspect the cam through the valve adj holes for any obvious wear possibly caused by oil starvation.

Well, since you cannot see the bearing surfaces, you ain't gonna see much. The aluminum plain bearings of the camshaft are the weak spot of this engine. Use the best quality synthetic oil and change it regularly - at least once a year, regardless of mileage.

now to your question:

I have a Tour with 12k miles and when in third or fourth gear between 3k and 4k rpm, I get an engine rattle.

the possibilities:

-valve adjustment: especially the forked rockerarm for the center and right intake valves can be tricky to set. 0.10mm intake, 0.15mm exhaust cold. Normally however, no adjustment is necessary. I have seen a locknut (M6x0.75) come loose, however, and that is very audible.

-the less serious: gear pitting. THis is normal for the 5th gear and to a lesser extent for the 2nd. I have not heard of it for the other at mileages below 40tmls. The pitting is cause by high gear load at low RPM. THe motor is not a thumper, despite its displacement and cannot take continued use at RPM below 3,5- 4000. Just don't do it unless you have flat slide carbs and a really skillful right wrist.

-serious: the Woodruff key in the crankshaft for the primary gear and the countershaft drive gear may be making the noise. This happens unfortunately far more often than Yamaha is willing to admit. When it gets play, this will increase until the the key is sheared off, at which moment the counterbalancer and crank will meet for the first and the last time...
Less often but also possible is damage to the keyway of the counterbalancer which in the end can cause the same BIG trouble.
If you cannot find teh cause with the first two possibilities, remove the side cover and check the primary gear train. Otherwise it could get very expensive indeed!

[Bill Jurgenson]

Did you clean the oil return screen below the battery ? If that screen gets blocked, oil pump pick up is reduced and the cam tensioner might not tension the cam chain.

hum. The chain tensioner is automatic, but it is not hydraulic. It is a simple spring ratchet mechanism that couldn't care less if there is enuf oil in the engine or not. Not that it cannot cause problems - it can - but under normal usage and rpm range, it is pretty foolproof. If you ever do have reason to remove the tensioner, be sure to lift the ratchet and set it back before reinstalling it.

If you have a real problem whatever metal is in that screen could be a clue...

Since that screen is in the line from the tank to the engine, you do indeed have real problems if there is anything metallic in it!

Also inspect the cam through the valve adj holes for any obvious wear possibly caused by oil starvation.

Well, since you cannot see the bearing surfaces, you ain't gonna see much. The aluminum plain bearings of the camshaft are the weak spot of this engine. Use the best quality synthetic oil and change it regularly - at least once a year, regardless of mileage.

now to your question:

I have a Tour with 12k miles and when in third or fourth gear between 3k and 4k rpm, I get an engine rattle.

the possibilities:

-valve adjustment: especially the forked rockerarm for the center and right intake valves can be tricky to set. 0.10mm intake, 0.15mm exhaust cold. Normally however, no adjustment is necessary. I have seen a locknut (M6x0.75) come loose, however, and that is very audible.

- gear pitting. This is normal for the 5th gear and to a lesser extent for the 2nd. I have not heard of it for the others at mileages below 40tmls. The pitting is caused by high gear load at low RPM. The motor is not a thumper, despite its displacement, and cannot take continued use at RPM below 3,5- 4000. Just don't do it unless you have flat slide carbs and a really skillful right wrist.

- the cog: I have seen the locknut put on backwards by a dealership shop. This done, the nut is tight but the gog is not and the splines will eventually shear off.

-serious: the Woodruff key in the crankshaft for the primary gear and the countershaft drive gear may be making the noise. This happens unfortunately far more often than Yamaha is willing to admit. When it gets play, this will increase until the the key is sheared off, at which moment the counterbalancer and crank will meet for the first and the last time...
Less often but also possible is damage to the keyway of the counterbalancer which in the end can cause the same BIG trouble.

If you cannot find the cause with the first three possibilities, remove the side cover and check the primary gear train. Otherwise it could get very expensive indeed!

[jimc]

Is it possible that the primary gear rattle could be related to the cold start rattle that makes me crazy? Cold starts exhibit a light ratchet type rattle for about 60 seconds. Bike has done this since new, but i don't have high mileage yet. Almost sounds like a kickstart ratchet...but i don't think the e start uses a toothed drive.
Valve clearances are OK, and oil change doesn't affect it.
Thanks,
Jim

[hb7]

"damaged keyway in a counterbalancer of an xtz engine..."

Bill, is that damaged keyway a stock engine or a modified higher horsepower engine ?

[DAVID THOMPSON]

the nut on the counter shaft sprocket needs a torque wrench
and loctite non hardening and also a metal tab type lock washer or they will come loose
my rotax engine book says 221 Violet.see below

222 Violet, Low Strength Thread Locker. For 1/4" diameter and smaller fasteners. Where "Thread Locker" is specified in Rotax documentation, that spec is generally European version 221 Violet. 222 is the correct US equivalent
see link for past post on the rotax powered bikes here
http://www.mzriders.com/mz/viewtopic.php?t=944

i do not like to glue things together but i always loctite the sprocket nut
as i do not like working on bike transmissions
it cuts into ride time and naps under a good shade tree on a hot day
ar dave

[sandberg]

I found some time to look at my valves and the intakes were ok but the exhaust wouldn't let a .10mm through. That was a bit tight so I am wondering how the clearance is to the top of the piston. Could I have possibly touched them? I set them to .15-.20mm and took it for a short ride and it actually seemed 90% quieter although not completely gone. Above 4k and there is no noise.

On another subject, there is a large hose that runs over the top of the carbs and attaches the top of the crankcase to the airbox. It was in the way so I ran it through under the carbs. It is now looped. I don't know what it does or if it is even necessary? Maybe a anti-pollution device or something. It would take much to block it off.

[Bill Jurgenson]

The valves will never "kiss" the piston with the stock cam. It ain't possible - or rather only when the timing chain breaks. Not even possible with a stage 3 Megacycle cam still using the the stock springs. The valves just float above -8000rpm. Nothing else happens as I know from experience. And lots of experience with broken timing chains, too, in the racing engine, which is why I use a different chain and chainwheels in it.
When the tolerance gets too small, you run the risk of burning the valves and/or seats because they do not close dependably and the burning charge forces it way out thru the gap.


The hose is the crankcase vent. Don't shorten it. In fact, if anything, lengthen it. Since yours goes over the carbs, it is the later, longer version. Better to leave it as it was. tho it shouldn't really matter. Just pull it off the airbox when you want it out of the way to work on something. Check the inside of the airbox periodically for oil blown into it thru that hose. Some engines are dry, others blow a bit - most I think - and some blow a very lot, all "new out of the box". I have had or rebuilt enuf of them to have a certian amount of experience.

[Bill Jurgenson]

Bill, is that damaged keyway a stock engine or a modified higher horsepower engine ?

from a stock SZR engine used in a custom built sidecar bike.


Personally, I don't use Loctite unless it is unavoidable, certianly not on the sprocket nut. using the proper torque for the thred and a NEW lockwasher is more than enuf security.

[sandberg]

Thanks for all the info. I'll put that hose back where it belongs. I don't think I will get that far into the engine to replace the cam chain and wheel. Sure would be nice to find someone close by with your kind of experience. In the meantime the bike seems ok as long as the revs are up.

[hb7]

You know, it wouldn't too hard to record the sound of your rattle and post it on http://www.zshare.net for all to hear....

[sandberg]

I would have to get a microphone down by the engine and secure it there while I am doing 30 mph running down the road. But I don't have a microphone and holding my camera while making an mpeg would make it tough for me to use the clutch. What was your plan?