Can these motors take the extra power?

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Rocky_Motor

Rocky_Motor

New Member
Nov 14, 2011
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Fort Collins & Boulder
I've been thinking of getting an expansion chamber and thatsdax's carburetor after my engine is broken in. But I got to thinking that since these engines aren't particularly high quality, do performance mods just kill motors?


Soo, for those who have increased the power output of your motor, have you found that your motor tends to break a lot? Or does it run with more power and no problems?
 
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vachon644

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Nov 27, 2011
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Quebec city, QC, Canada
I think that expansion pipes designed for the HT engines are tuned for low rpm rather than high rpm and that alone should not cause any harm to the engine. As for the carb, if properly tuned it shouldn't cause any troubles either. It's obvious that straining the engine at high rpm will make the piston rings wear out faster but I never heard of an HT engine which stopped working due to normal ring wear resulting in too low compression. That said, I do believe that poor maintenance is far worse than performance mods.
 
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ivan H

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Oct 8, 2011
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I think the weakest link on these motors is the bearings used in them, especially the small end which is a 10x14x13 & the piston pin bosses are about 17.5mm apart allowing bearing drift. Replace with a quality 10x14x15 & the crank & countershaft bearings with quality items. Center & end float crank to .004" & properly align the countershaft before torqueing the cases to 75inch/pounds & it'll be much more reliable & able to handle any extra power. Cheers
 
F_Rod81

F_Rod81

Dealer
Jan 1, 2011
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Denver, CO
My old Grubee GT5 has about every mod out there that you can buy other than a shift kit. It is dialed in perfectly and is considered the fastest MB in its class in Colorado. I built it good and it is still running strong as a daily rider with very little to no issues. It all depends on the operator.
 
Al.Fisherman

Al.Fisherman

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Sep 9, 2009
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F_Rod81 said:
My old Grubee GT5 has about every mod out there that you can buy other than a shift kit. It is dialed in perfectly and is considered the fastest MB in its class in Colorado. I built it good and it is still running strong as a daily rider with very little to no issues. It all depends on the operator.
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You explained it all... It's not stock out of the box.
 
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ivan H

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Oct 8, 2011
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The small end bearing is the main one to be wary of because of not being wide enough, if u check the forums people do have problems with. The others wont fail, they're just not quality, a couple of mine were really notchy. I replaced with NTN bearings. Also, one of the countershaft bearings was a kinda loose fit in the case, maybe to allow for alignment of the shaft as the cases provide no means of aligning this shaft. I seated it with loctite bearing retainer. I have mild port work, rocksolid head, vm16 mikuni, sbp x chamber & shiftkit. The motor sound a lot better with the bearings replaced, nowhere near as rattly. Cheers
 
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ivan H

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Oct 8, 2011
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yeah, at 3.5mm wide that seal doesnt offer a great purchase on the case does it. Have u considered using a seal adheasive, I think loctite has a product,,, or even silicone. Cheers
 
Rocksolidperson

Rocksolidperson

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Feb 11, 2012
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the engines can run the higher performance loads, look at my build thats in my signature, i have done 8000km now and still going great no probs at all, just run good oil at a not to much amount and they will go forever
 
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motor_bike_fanatic

New Member
Jul 26, 2011
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Pennsylvania
There are some performance mods that can shorten the life of these engines, especially when done improperly. Improper porting and piston skirt trimming can seriously harm any small engine. These engines also do not like to be bored out, at least from what I have heard. But expansion chambers should not cause any harm. I have had an expansion chamber for almost a year, and as far as I can tell its not hurting the engine at all. The important things that will keep your engine alive as long as possible are the proper oil, proper air/fuel mixture, and properly tuned carb. There are a lot of people on this forum that seem to think that when you install an expansion chamber, you need to re-jet your carb in order to obtain the proper air/fuel mixture. That hasn't been my experience. I am running a pocketbike pipe with a stock NT carb, and my spark plug has remained an even brown color since I tuned my carburetor. I have done nothing else to my carb or engine since installing the pocketbike pipe, except for installing a port-matched intake gasket.
 
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ivan H

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Hi Rocksolidperson,, so, the main bearings in these can fail. A couple of the bearings I removed were really notchy & only a few months old so no doubt they would have excessively worn in time. Are u running a rocksolid motor now? I got mine from zbox before I knew about rocksolid, but the bearings I put in for crank & countershaft are the same NTN units listed on their site. I used a 10x14x15 for the small end as its 2mm wider than the stock bearing. Cheers
 
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Lightster361

New Member
Sep 6, 2011
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Texas
ivan H said:
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I think the weakest link on these motors is the bearings used in them, especially the small end which is a 10x14x13 & the piston pin bosses are about 17.5mm apart allowing bearing drift. Replace with a quality 10x14x15 & the crank & countershaft bearings with quality items. Center & end float crank to .004" & properly align the countershaft before torqueing the cases to 75inch/pounds & it'll be much more reliable & able to handle any extra power. Cheers
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And were do I find these bearings? Thanks zpt
 
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ivan H

Member
Oct 8, 2011
622
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australia
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Hi Lightster361,, I'm down under in Oz,,, but if ur having trouble finding quality bearings, the 6202's u can order from Rock Solid Engines. They're a 20,000 rpm rated bearing. The 10x14x15 I got from sunstate bearings but there's a link to a quality item in a thread on this forum, I'll find it & get back 2 u. Cheers
 
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ivan H

Member
Oct 8, 2011
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australia
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Ok Lightster, I just remembered, (I'm still on my first gallon of coffee). Check out the thread entitled "need help with piston bearing". Someone posted a link to a quality 10x14x15 in the states. Cheers
 
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ivan H

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Oct 8, 2011
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australia
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Yeah, they r a little pricey but u get wot u pay 4. At under $25 including freight its a good price 4 peace of mind. U know it aint gunna fail no matter how hard u rev it. Cheers
 
Das Chicken

Das Chicken

Member
Mar 22, 2012
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Georgia
ivan H said:
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Hi Rocksolidperson,, so, the main bearings in these can fail. A couple of the bearings I removed were really notchy & only a few months old so no doubt they would have excessively worn in time. Are u running a rocksolid motor now? I got mine from zbox before I knew about rocksolid, but the bearings I put in for crank & countershaft are the same NTN units listed on their site. I used a 10x14x15 for the small end as its 2mm wider than the stock bearing. Cheers
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Are the 48-49cc and 66cc bearings the same? I'm using a stock (port-matched exhaust) 48-49cc engine. What are the crankshaft bearing sizes? I made the mistake of running outboard oil in my engine. It's got about 440 miles on it, and the cylinder wall already has scratches deep enough to feel with a fingernail. :-|| I switched to air cooled oil after about 4/5ths of my second gallon of gas. Any idea where to get cheap cylinders and pistons, and QUALITY bearings? I'll put up a video of it running soon, and tell me what you think about it's condition. I'm not going for a performance bike, just trying to stay reliable. Thanks.
 
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