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xr50 88cc big bore kit


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alright...

so for those who dont want to read thru the whole thing, heres my questions...

1) getting a sharp noise when kick-starting... no noise when turning over by hand, no noise when running... any ideas?

2) what is proper break-in procedure for big bore kit?

so after about an 8 hour ordeal, we got the big bore kit installed... put oil back in it, turned it over by hand a bunch of times to make sure everything was ok... seemed to be ok, a little tougher at one point, but not stopping or anything... so we decided to try to start it...

kicked it slowly a few times to get gas runnin thru, then it sounded for a minute like it was gonna catch, but made a "bang" and stopped... this kinda worried us, werent sure what that was about... but decided whatever, try again... made the same noise, but started and surprisingly enough =P, seemed to run real smooth... idle was kinda high, but we havent done any adjustments to the carbs yet...

as far as i know, we did everything by the book, only thing i wonder about is the camshaft... instructions said to insert the new one with the cam lobes facing down, which i took to mean not lifting the arms... theres only two ways the timing sprocket could screw onto the camshaft, so we went to the closest one once we had the parts together... seems to me like it wouldnt run if this wasnt correct?

anybody know what this noise might be? it almost sounds like a backfire, but sounds a little metallic too... so far, we have gotten this noise everytime we kicked it over... no noises when cranking over by hand, and no noises like that when running... so not sure what thats about...

other question is, what is the proper break-in procedure for the big bore kit? one of my buddys was convinced that you have to let it idle or ride around slowly (keeping the revs down) until it reaches operating temp, then shut off, let it cool down, and repeat this a few times...

my other friend was convinced that you should ride it like you normally would (aka, beat the crap out of it =P) until operating temp, let it cool down, and repeat a few times...

im leaning towards taking it easy for maybe half a tank... other way sounds like a good way to blow up stuff...

any input/comments/suggestions greatly appreciated!!

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I'm not sure what the sound could be, could you maybe make a video so we c ould hear it?

On the timing, you just need to make sure when the piston is at TDC the O on the came sprocket lines up with the < notch on the head. Typically the O will line up with the TOP portion of the <, not the bottom portion.. IT's never perfectly in the middle, kind of weird.

As long as the O lines up with the < at TDC, the motor is in time. However you COULD install the cam 180 degrees out.. Which is still perfectly fine and the bike will run fine, HOWEVER, you'd have to adjust the valves with the cam sprocket 180 out.. (so the came would be in proper position)

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And for breaking it in, you should NEVER run it hard tell it has a coupe heat cycles. IMO the worst thing to do is run it hard right from the jump without at least letting it fully warm up.

My personal way for breaking in, is the first start up just fire it up, and let it idle, maybe giving a couple blips of the throttle but keeping below about 1/4 of the total RPM.. Let it warm up 5-10 minutes, then shut off and let it cool 20-30 minutes..

Then fire it up, let it warm up 5-10 minutes, then maybe take it for a slow ride around the block going up to about half rpm, then shut it off and let it cool 20-30 at least..

Then a third time fire it up, warm it 5-10 minutes, go ride it for another 5-10 tell it's fully warm, then open it up and enjoy it! Maybe take it a little easy the first day, not holding on rev limiter for long periods of time. But after 2-3 heat cycles it should be good to go.

I always at least heat cycle a motor, but I end up running it hard after a couple heat cycles, then letting it fully warm up.

Also I'm a whore for always letting my motors warm up, on my dirt bikes every time I ride I let them just sit there idling and warming up for at LEAST 2-3 minutes, then I take it easy the first 5 minutes tell its at 100% full operating temp, then I give my bikes hell.

Even my car I let warm up for at LEAST 20-30 seconds before driving away, and my sport bike I also let idle 1-2 minutes tell it starts to show temperature on the temp gauge before moving. Just my way of doing things ­čĹŹ

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thanks for the tips on breaking-in!! and i figured out what the noise was...

i brought it in to work today, had one of our mechanics look at it... figured out that the gasket between the head and the jug was leaking/faulty/not installed correctly/didnt torque headbolts to spec... or some combination of the above...lol... apparently it was blowing out the side... he revved it up a bit, which i didnt do for fear of ruining something, and it was definately poppin and blowing smoke out the side between the head and jug...

so now i have a whole new set of gaskets coming (because of course you cant buy just that one =P) , and gonna hafta take the head off when they come in, reinstall a new gasket, and hopefully that will fix it... i believe that is the only problem, the mechanic said other than the gasket leak he thought it sounded like it ran fine, timing was ok...

i do have two more questions however...

sorry in advance for the crappy quality of the pics, they were taken with my phone at night...

first question is, what the hell is this black box?

IMG00032-20100322-2012.jpg

originally had a tube coming from stock air intake, but no hookup on the new air filter, so i just left it open... bike runs without it, so im hoping its not too crucial, but im wondering if i should at least rig up something to keep crap from getting into it...

second question... for those who have installed the big bore kit... it may be kinda hard to see in this pic, but my carb overflow nozzle runs almost directly into the top of the jug, with no room for the overflow tube... how can i get around this? can i bend the nozzle outwards, or will i snap it off? i dont think i want gas spilling onto the jug/head after running hard for an hour or two... =S

IMG00034-20100322-2012.jpg

comments / suggestions appreciated!! =)

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for the vent tube, I personally just bought some tube from a hardware store, and run like a 1 foot long tube that dumps to the ground lol... I dont run a filter, I just chain my oil every 4-8 hours or so of running my bike

and do you have a plastic carb spacer between the head and carb manifold?

Also my carb drain tube was pinched, but still would let fuel out. I never worried about it since it worked, but mine was definitely pinched bad with the tube on it lol

And about your previous problem, my friend had that same problem. I installed his big bore and torqued it properly with a NICE torque wrench I borrowed it.. I ended up finding out a decent amount of ppl have this problem. You just have to over torque the head bolts a little lol

8, or 10, or 12 or whatever ft lb's the torque is just isn't enough to always seal, even with a brand new jug/head gasket lol

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ooh reread your post and see you didn't fix it yet and ride it

I'd just retorque the head bolts to spec, start it, see if it pops.. If it pops, just tighten the head bolts a little, like 1/8-1/4 turn on the each bolt in a criss cross fasion.. Then start and see if it pops, continue tell it stops (don't go much over like 30-40% or so over torque...)

It's a pretty common problem. You can actually most the time reuse a used head gasket.. And since yours has very little run time, and never sealed, you should still be good to torque it tell it quits poping..

Btw I'm not always a 'ghetto engineer' I also have swaped head gaskets on cars, sport bikes, and full sized dirt bikes/quads... But these 50's head gaskets can sometimes be reuse, and commonly have problems sealing at their LOW stock torque specs for the head bolts

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ooh reread your post and see you didn't fix it yet and ride it

I'd just retorque the head bolts to spec, start it, see if it pops.. If it pops, just tighten the head bolts a little, like 1/8-1/4 turn on the each bolt in a criss cross fasion.. Then start and see if it pops, continue tell it stops (don't go much over like 30-40% or so over torque...)

It's a pretty common problem. You can actually most the time reuse a used head gasket.. And since yours has very little run time, and never sealed, you should still be good to torque it tell it quits poping..

Btw I'm not always a 'ghetto engineer' I also have swaped head gaskets on cars, sport bikes, and full sized dirt bikes/quads... But these 50's head gaskets can sometimes be reuse, and commonly have problems sealing at their LOW stock torque specs for the head bolts

yeah, i would reuse the gasket, but in finding out the problem the gasket got pretty well ruined i think... lol

i also borrowed a torque wrench from a mechanic at work, and will use that when i replace the gasket... hopefully that will fix the problem...

from what i've seen online, sounds like torque rating is 10ft/lbs. for the headbolts... figured id start with that, see if i get any pops, and go up a little at a time from there if i get any...

we'll see what happens once i get the gaskets... =)

one other issue is there seems to be a mushy spot in the kickstart were it almost feels like its slipping... let up to the top, and it grabs again...

the mechanic said he figured it was from loosing compression thru the gasket, but im wondering if there is anything else it might be...

guess ill see if a new gasket fixes it, but any ideas on anything else it might be?

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most likely the clutch slipping, does it make sort of a 'whir' sound when it happens and sound like the motor isn't spinning over?

It's happened on almost every single bike I put a 88 kit on, the stock clutch can't handle the compression at the low speed it takes to kick, and sometimes slips

Have to pick up a HD clutch, or a manual clutch to fix the problem. I put about 3 years on my honda trail bikes HD clutch and it still is holding up great and never slipping when kick starting my bike

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most likely the clutch slipping, does it make sort of a 'whir' sound when it happens and sound like the motor isn't spinning over?

It's happened on almost every single bike I put a 88 kit on, the stock clutch can't handle the compression at the low speed it takes to kick, and sometimes slips

Have to pick up a HD clutch, or a manual clutch to fix the problem. I put about 3 years on my honda trail bikes HD clutch and it still is holding up great and never slipping when kick starting my bike

not sure, it doesnt really make a noise, just feels like its slipping... ill hafta deal with that later, once i actually get this thing running... see story continued below... =\

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well thanks to some super fast shipping, i got the new gaskets today, i was all set to go with a torque wrench borrowed from my work...

tore the head off, put the new gasket on, started putting everything back together, and thats where things started going wrong...

either i dont know how to use a torque wrench, or 10ft/lbs. is too much for the head bolts... the 3 acorn nuts torqued to specs fine... but it was the weirdest thing i ever seen, it stripped the inside threads right out of the last plain nut and left them sitting on the headbolt... course i had to ruin the threads on the headbolt while getting the stupid nut back off...

then i also managed to snap one of the timing sprocket bolts off inside the camshaft... 6.5 ft/lbs. on that bad boy didnt seem to faze it the first time we put it together, must have weakened or something...

managed to pull the remainder of the bolt out with an extraction drillbit, so thankfully i shouldnt need a new camshaft at least... only good news of the day... i did get a metal shaving or two in the bearings from drilling the bolt out, but blew air through the bearings real hard while spinning them, and that seemed to get rid of it...

so now i need a new headbolt and nut, and a timing sprocket bolt... and hafta figure out what to do for torque ratings... idk...

i just wish i could get this stupid thing running good enough to ride it... would relieve some stress... i was about ready to kick the thing into the wall when those bolts and nuts snapped...

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ALRIGHT!! ENOUGH SCREWIN AROUND!!

of course nobody has the parts i need in stock, they're all gonna be a couple days out...

so instead...

borrowed a mechanics "thread restoring kit" , needle torque wrench as opposed to a clicker...

ran to the hardware store, got me a new nut and two screws for the timing sprocket... he didnt have hex heads in that size, only philips head... also grabbed a tube of red locktight...

went home, used the die on the headbolt, managed to clean it up halfway decent, threads were still a little mushed but not horrible...

threw everything back together, couldnt really torque the timing sprocket screws, so just tightened them as best as i could by hand and called her good...

torqued the headbolts down with the needle torque wrench, with locktight on the headbolt with the hex nut... didnt torque them to 10 ft/lbs., called it more around 8-9 this time...

turned the flywheel a bunch of times by hand to make sure nothing was stickin... first kick started it right up... rode it around the yard for about 10 minutes with low revs.... then shut her off, retorqued the headbolts and checked the oil...

then said to hell with breaking it in, i need to do some wheelies...

cracked the throttle a bit, holy hell that thing runs like a raped ape!!!

was doin sitdowns in 3rd gear no problem, when before i had to stand on the back pegs and physically yank the front end off the ground... lol crazy fun...

seemed to run fine, no backfires or anything, only thing i noticed after a little while is that if i rev a bit under load, i hear a faint metallic knocking...

any ideas what this might be? valves not adjusted correctly? timing chain off?

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