Engine Balancing

[360sprntr]

Hello Everyone! I began my gasgas experience two years ago with a low hour demo 07 300.Sent Forks and shock to LTR, head & carb to rb.Getting everything as dialed in as possible.Very happy with everything about the bike except the vibrations,which I found unacceptable. I tried most traditional aids for motorcycle vibrations, all having noticeable benefits but none being the cure only an aid. I was willing to look within in case it was me hanging on to tight, even though previous machines had not left my arms asleep at night. Liking the bike very much except for the vib's, I decided to go after what I belief to be the root cause, engine balance. I'm usually a do it yourself-er, but decided to treat myself to a complete rebuild at surf and turf, who specialize in crank truing and balancing. Being one of very few shops capable of performing single cylinder two-cycle crankshaft balancing.Well very long story told short this has been an amazing experience! The ignition inertia weight was left out and balance corrected.Kick starts perfectly,does not stall, awesome bottom end and must have gained a couple thousand in over-rev.I would do this to a brand new bike before ever riding it! It has to be something that would pay for itself in reliability. If this thing didn't make noise you would swear it was electric! I strongly recommend making a good thing perfect, balance your gasgas. I stepped out of the box and would like everyone to benefit. Would be more than happy to answer any question.Bill

 

[GMP]

Good post. I'd do it the next time I rebuild one. Did you also have the ignition flywheel balanced? I'm pretty sure Trail Tech provides that service.

 

[case-racing]

balance

Ok i'm interested, so what part exactly are we talking about, i can't picture it in my head, the Gas Gas quad i have has very bad vibrations too the point i am snapping engine mounts, i had to remove my balance shaft as i twisted it and getting bits in Australia for it is a pain in the arse. if you could take a picture of it that would be awesome.

Cheers Bill

 

[360sprntr]

Sorry there will be no pictures, as my motor is together and running. It's a procedure that would be done during a rebuild as the crankshaft will need to come a part and reassembled with a solid mass of weight that does not swing so it can be spun. I'm on to work right know but I'll post web sight if there is interest,but I believe it to be surfnturfracing.com.Check it out there's picture's and info. Were you live you'll probably need to research who can do it. I live in Oregon, but sent my engine clear across the country. After researching were it could be done.

 

[GMP]

Thats close to me and right in NETRA land. Now I'm more pissed my brother sold the GG 125 before I could get it. I'd have these guys do a big bore before an EG hack for sure.

So what did you end up paying if you don't mind? i see the prices vary depending on what they have to do.

 

[ramcclure200]

I feel your excitement, I had to rebuild my 90 RMX motor back in 92? i think and at that time Noleen Racing was doing balancing let me tell you that motor was smoothhhh and a double joy to ride, money well spent for sure.
Enjoy your New bike and you will be less tired after a long ride now

 

[farmerj]

Bill, I am really interested in that.

(1)From what I've understood, a crankshaft can only be balanced for a certain part of the rpm range. Did your engine end up smooth all the way through?

(2) "The ignition inertia weight was left out" - Which part is that? I don't want to lose any flywheel-type weight, as I'm after the "no-stall factor" down low when plunking around on hillsides. Do you really still have the same "bottom end?"

Glad you found engine balancing a good solution!

Jeff

 

[Hawkeye]

Hmm. I was thinking about installing the GG counterbalancer in my 2001 300 just like I did my 2002. Now I'm thinking of having the '01's crank balanced and then I can compare the two...

http://www.surfnturfracing.com/services/crank-work/crank-balancing

Looks like prices will be between $375 and $475 for disassembly, balancing and reassembling. The higher price would be if they have to add weight vs. having to subtract it from the crank.

 

[360sprntr]

Howdy Glenn, I had to check out if my flywheel had been balanced. It was not, which surprised me and glad you asked. I will be checking that out for sure. As for how much it cost, remember I was treating myself. So I went all out with all new part's no work on my part. It cost $1185. returned to my house. Money well spent, as I would not trade for a brand new bike! When I was making the decision on what to do, STR was more than willing to let me supple all the new part's and send motor in pieces. But I just sent the whole motor and bought part's though STR.
Thank's Bill

 

[360sprntr]

Howdy Jeff, I was under the same understanding as yourself about RPM range. This guy has it figured out and nailed it! Very good everywhere, it just rip,s! It definitely will rev much higher effortlessly than before. The inertia weight is behind the clutch basket, and yes it really does have just as much bottom end. I was also skeptical and made contact with steahly offroad to custom build a flywheel weight for my ec ignition,which he will. Have a friend that would cnc a cover spacer,just in case. After riding it , I'm very happy and no longer have that concern. I also crave bottom end grunt, that's the reason for the 300. But was willing to give that up for a smaller bike if I couldn't solve the vibration issue. Ended up getting the best of both world's. Money well spent! Oh Ya it doesn't stall I tried.Bill

 

[farmerj]

Great info., Bill. I have more questions!

(1) Do all 300s vibrate the same amount? Or are there differences between individual bikes from factory anomalies or slight tolerance differences during assembly?
(2) Does jetting affect vibration tendencies?

Thanks,

Jeff

 

[360sprntr]

Howdy Jeff! I would think every motor could be slightly different for the reason's you mentioned, I know the crank being dead true to be very important. Always use the best part's and best machine shop, over time I believe you'll have best result's. I ride with a friend that has an 11 ktm 300 with flex bars and we switch bikes at least once a ride. Before the work on my bike, his vibrated less, was soft on the bottom end but was way stronger on top. I was considering getting one but liked the gasgas power better so went after making it better. Went riding with several guy's who had rode my bike before and none could believe how good it is, bottom may be better,top much better. Run's harder on top than the KTM now. The only problem I had was I got stuck on a RM250 for a while and had a hell of a time getting mine back. Also vibrates less than the KTM and I don't have flex bar's. I do think jetting to be a factor, that's something I'll share on a different post as mine is very good and worth sharing. Mines so smooth and linear it seems electric, I don't even feel a power band, pull's hard down low and rev's to the moon. with no big hit anywhere just strong. Much more like a well tuned 4cycle, my friend's call it a 3cycle. I used to say my favorite bike was a new one,now It's a dialed in one!Bill.

 

[GMP]

Bill,

By cost I meant the crank service alone. Was it the basic work or did it cost more for heavier weight added? All GG cranks, at least the 250/300s, should be the same and prospective customers will know what to expect. I also think most would do the R&R themselves and just send the crank, piston kit, and rod kit.

As far as the primary eccentric balance weight goes, it was changed from a round 10oz weight to the 8oz eccentric in '01. '97 and '98 engines with the counterbalancer had the drive gear in this location. The MC motocross bikes had a simple spacer probably like what they put in yours now. One of the three is required to capture the crank to the right side main bearing inner race. I had a '00 with the round weight and swapped in the eccentric to see if it made a difference in vibration. It may have helped a little or changed the harmonics around a bit. Point is if you can find one of these from a '99/'00 it will give you slightly more inertia without affecting balance. It would be similar to adding a 10oz weight to a 2K-2 flywheel as the diameters are close.

I sold my '00 to a friend nine years ago and gave him a box of parts including the weight. He still owns the bike, so I'll bet its still on a shelf somewhere.

 

[lankydoug]

When I used to build (car) drag racing engines we balanced everything 100% of the time. Once we figured how much 1 gram out of balance would affect a V-8 with a 4" stroke at 7,000 rpm and if I remember it was like 75lbs out. A short stroke 2t would be less but the rpm increase would have a big affect. Balancing is a big plus for dependability. I remember the price being $100 plus mallory metal if required. I'm sure it's higher now days since that was 15 years ago but any automotive machine shop that does high performance balancing could do it.

 

[360sprntr]

Howdy Glenn ! That is a great idea, I could even build it myself and play with weight's. I like that better than a fly wheel weight. To be honest I haven't felt the need, but it would be fun to see what happen's. I'll have to find my bill, but I'm sure heavy metal was added as it was under balanced by 20 grams. I'd like to know if the weight you mentioned is available I'd be willing to be a gennie pig. Thanks Bill

 

[360sprntr]

Howdy Glenn! I just reread your last post and between us I believe we proved that balancing will be beneficial, by comparing are experiences. I'm sure glad I finally joined this forum! Thanks Bill

 

[GMP]

The space behind the crank pinion is limited as it was originally designed for a counterbalancer drive gear. You can't go too thick, I'd say your close to the limit with the old OEM weight.

 

[Neil E.]

Bike to bike differences are mostly from trueness of the crank. There is quite a difference between a perfect crank and one that has .002" runout. Some manufacturers consider .004" runout to be 'within spec'.

I'm one of the folks that prefers a heavy flywheel. If there was enough room on the primary side, I'd add more weight. Just the diameter of a drive gear wouldn't be much extra inertia. The primary side is a better location for weight as the inertia forces wouldn't have to be transfered through the crank.