And then there were two.. 1976 GT250 Rebuild

hurco550 said:
Yep xb I was thinking what Tune-A-Fish was thinking about the deck. Never thought to break the burr on the ports, or I should say I never have before lol
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I've experienced the results of a few machinists telling me "just use some emery cloth on them,it should take care of it.." it didn't ::), xb is right,it needs to be done.I had a small chip come off the edges of the ports and it ruined a fresh bore job on a 2 stroke in the past.
I just used my Dremel w/ a round stone on the last 2 stroke cyl. and deburred my ports no problem.
I've been experiencing LOT'S of weird machinists in the past 1+ yrs. and I'm just wore out from their 'advice'.I'm looking forward to getting in touch w/ that man at mototechUSA & seeing what he'll tell me about his work.I had a crankshaft (XR200)rebuilt by "a precision machine shop" recommended to me by another forum dude on another forum and I think it was the first time that he did a 3-piece crankshaft... I hope he was able to align both crank wheels to a very close tolerance.I need to ask the machinist in Mansfield if he would check the crank and see how 'true' it really is,if he does that type of work.I also want to get a big bore sleeve installed in a CB125;I wonder if he does that type of work? I'm going to call him next week.
 
pluss the rings are not happy with any ex port, its the width that is the issue the ring will naturally expand slightly into the port and the top edge is the issue this is where piston speed is high as well .tuners/designers learned that an exhaust port too wide will eat rings hence bridged ex ports.there is a simple rule of thumb limit to ex port width per bore size.bottom line is any ex port should get a little extra care on the upper edge with a nice smooth champhered radiused transition,nothing huge, just enough
and considering your machinist prowess you should make sure the squish band is down where it needs to be, most stock stuff is set too big
best thing to do is first cc the chambers and then if you need to drop the suish down you can bring the dome back so volume is maintained
 
Got all ready to chamfer the ports, then upon closer inspection, the guy I had bore them had already done it. . So that's that.
I got my gasket set in and was about to do the re assembly
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The bad news... I didn't realize that gt250s came with either 14mm or 16mm wrist pins. And of course I need the 14 and bought the 16... so hopefully new pistons on the way soon. I am gonna measure mine really close and hope the new ones come in close. If not I'm gonna have to bore again another .05mm over. . Blah
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Wow, that is really bad news about the wrist pins... Dang, what crappy luck.
 
hurco,
I'm hoping that piston seller will be good to you and just give you an easy exchange;I like that old blue shop air compressor, ;).What brand is it ?
 
Well, the piston seller was more than happy to exchange the Pistons if I covered shipping both ways. The only problem is that it would have cost me more to ship the wrong ones back to Japan than it would have been more than just buying new ones. So I just bit the bullet and ordered them, and they came in today. I have to give my engine guy a call as I had my cylinders bored to the "wrong" pistons. The new ones came in only one thousandth (.001") smaller at the skirt. I am hoping that this isn't too much. Oh well, live and learn. .
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Glad to hear your back with it hurco.I just spoke to Chris(the machinist) this morn. about sending my cyl./piston out to him tomorrow and he's a good dude about that.
Did you get those pistons from Japan as in 'oem Suzuki' ?
 
grcamna5 said:
Glad to hear your back with it hurco.I just spoke to Chris(the machinist) this morn. about sending my cyl./piston out to him tomorrow and he's a good dude about that.
Did you get those pistons from Japan as in 'oem Suzuki' ?
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Thanks man. They are aftermarket, I can get nos suzuki standard size pistons, but not over size
 
xb33bsa said:
bead blasting the skirts will bring em up a bit ;) you could coat them while yer at it
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Where do you send yours to get em coated?
 
xb33bsa said:
yeah bake pretty simple process though
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wow pricey, but may worth it while its apart. it says its just for domes, but you use it on the whole thing, or just the skirts?
 
xb33bsa said:
stuff i got is for the skirts not sure if they still sell it ..oh wait it is the same as the gear coat
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http://www.kgcoatings.com/products/3000-gear-kote

This what your talking about? Much less than the other stuff
 
hurco550 said:
Well, the piston seller was more than happy to exchange the Pistons if I covered shipping both ways. The only problem is that it would have cost me more to ship the wrong ones back to Japan than it would have been more than just buying new ones. So I just bit the bullet and ordered them, and they came in today. I have to give my engine guy a call as I had my cylinders bored to the "wrong" pistons. The new ones came in only one thousandth (.001") smaller at the skirt. I am hoping that this isn't too much. Oh well, live and learn. .
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hurco,
Let me know what the machinist says to you about the correct clearance for that;I'd rather have them on the tight side myself and then break it in slow and carefully,but that's just me..
 
The coating is going to be super thin mil but skirts opposite the pin only is good. as for tolerances 1K (1/2 really if that's overall) tight seems a bit snug to me, loose is worse but if the piston gets hot and leaves skidders it's gonna seize up faster than fat kid can eat an ice cream man.
 
Tune-A-Fish, great visual there, I'm no skinny kid... and I love me some ice cream.

Took apart the oil pump and cleaned it all up and checked everything out. Looks like she is good to go, so I slapped er on and re fitted the oil lines. The oil lines aren't hard, brittle or cracked, so I think they will be fine. I talked to my engine machine guy, and he said a half-a-thou a side more piston clearance won't hurt a thing, so I went ahead and put em on. Also got the stator back on after a trip to the hardware for bolts. For sitting Fer almost 6 years since I took it apart, those 3 bolts are the only thing I've "misplaced". Not bad if you ask me =)

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Also flattened down the decks with some 220 grit on top of a piece of glass to keep it flat. Finished out quite well.

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Cylinders and carb boots re installed. Man those boots were pricey. $37 a piece from Great Britain. The old ones were petty bad off though, and I don't wanna be suckin air.

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Gotta soda blast the head, and I should be ready to close er off.
 
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