i've always heard that it's easy to get a metrakit overbored if you seize it. well, i soft-seized mine rill bad . . . what now? specifically:
what parts do i order?
what sort of shop do i need to go to to get the overboring done?
does anyone know a good one in/near chicago?
what special instructions should i give them to get a good job done?
about how much should it cost?
any engine machine shop can probably do it on their rod hone. ask them to do it before you order the piston so they can tell you what size they had do finish the cylinder at.
the best thing to do it is look into your cylinder and check to see if there's any deep scratches...depending on the depth of the scratches, you need to determine the size of the piston you will need. the metra 65ccs come in 43.5mm(stock size), 43.7, 43.9, 44.1, and 44.3mm oversize pistons....when overboring you want to make sure that your not left with any scratches... as it defeats the purpose, as it may cause blowby
greg sorry but that's not the way to do it, as stated above the pistons only come in certain sizes...purchase the piston first, bring the piston and cylinder to the machine shop...they're gonna measure the piston size with a caliped....then they're gonna bore the cylinder to the size of the piston with a certain tolerance for piston expansion etc....you might wanna ask benji or 1977 if they have oversize pistons.... or order from metrakit themselves
Good luck finding a new metra piston. You will be able to see them on all the euro sites, but finding them in the US is going to be a challenge.
bummer dude what happened
No, do not buy the piston first as you do not know how far the machine shop will have to go to clean up the cylinder.
Just give the shop the sizes of the oversize pistons and they will stop at the smallest diameter that will clean the cylinder. Then buy the correct piston.
If Metra has a standard piston to cylinder wall clearance spec, give that to the machine shop. Otherwise the machinist will have to use his best judgement/experience in the matter.
FYI, the Honda Hobbit manual says that the stock clearance is:.050-.025mm max .150mm
I've found that the only shops that want to work on moped cylinders are ones that work on kids dirtbikes. Find someone that sells 50cc dirtbikes and ask them where you can get an overbore done. Then get that mechcanic to determine how far to overbore it, then get a new piston and have the work done.
The downside is that you are looking at hours of legwork, months of waiting, and easily over $100 is parts and labor. Maybe you should just get a new kit?
How bad is the seize anyway? Cast iron is usually pretty robust, you may not need to over bore it at all.
i'm not sure how bad it is, in a relative sense, since it's the only seized cylinder i've ever seen up close. what happened was, i was trying to get my 14mm intake off a week ago, but the manifold studs were bent, so in trying to lever it off with a screwdriver, i dug a big hole in my gasket. however, i also failed to get the manifold off on that particular day, so i didn't notice that i'd fucked up the gasket. then yesterday, i was heading over to tony's to try again at getting that 14mm intake off, and i was at wot for a few minutes with this massive air leak, and soft seized my engine. i'm a real genius. it also should have been really obvious to me what was going on, because the idle was high as shit . . . seriously i feel like such a f(*^&ing bonehead.
it's running now, though, with a 19mm carb installed, but i'm nervous to push it at all. it has a whitich, round mark on the cylinder, and a corresponding whitish, round mark on the piston. i guess i should get new rings, at least . . . i dunno.
i guess the first thing is to find out which shop can overbore the cylinder before doing anything...once that's taken care of then go ahead and send the cylinder in.
It's probably fine. Pull it apart and check out the piston and ring.
babooze, i work at a machine shop. we would waste hundreds of dollars a month if we just randomly ordered pistons without knowing what overbore we are going to need on the block. the final size is dependent on the damage caused to the cylinder. the machine shop will tell him how far they need to take it. if its beyond the largest overbore, then theres no saving it, unless they can knurl the piston (which i HIGHLY doubt). the overbore sizes for these motors are relatively close together, so he wouldnt have much problem at all having them clean it up and give him a measurement. he could then tell them what piston sizes he has available and they could finish it so it would work for the piston.
greg, you have a valid point on that....i kinda do my own assessments...and check to see what size piston i would need. i've done a fair share of overbored piston and i more or less judge for myself now a days... yeah, before i use to do it that way
but yeah if the machinist bores the cylinder to where there are no scratches left and if it goes past the biggest size piston it's useless to buy a piston...need to trash the cylinder.
Allow me to reiterate that your kit is probably fine. Pull the piston out and check the condition of the rings.
Im with bret on this one, you don't know what condition the cylinder and piston are in. Pull it apart at look for piston smear over the rings or gouging of the cylinder. Piston smear = new piston, gouging = either a trip to the machine shop ( I'm with Greg on that one) ora diy home job ifits not that bad. You can get a break hone at kragen that will chuck into a drill.
i'm sorry, i thought i posted somewhere above about this: i did pull the piston/cylinder, about an hour after the seizure. there's a large, whitish mark, like a bruise kind of, on the piston, and a corresponding one on the cylinder. the rings seem totally fine though. also, when i run my finger over the cylinder wall, it feels smooth . . . so i don't know. i ran the kit today, it seemed alright. i'm scared to ride it fast though . . . hm
hone it and sand the piston down. you shall live.
what is knurl????
Picture?
knurl is the raggedy sharp file-like edge on bike pegs and other metal bars for traction. when applied to a piston skirt, it raises the surface, essentially increasing the bore size the piston fits. weve got a machine to do it on auto pistons, what weve got is much too big for a moped piston but i bet theres a knurler out there that would work.
SOS pad and wd-40. Your cylinder will be fine. I had a metra kit bored out once. It only costed 50 bucks if I remember correctly. 40 or 45 for a piston. Saves you about 60 bucks from buying a kit. Gave me a couple extra mph too. :)
but try with an sos pad and wd 40 first eh? interesting. i'll give that a shot.
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