50mm taiwan bore info

JJ Joseph · Post by **JJ Joseph** » Fri May 11, 2012 1:46 am

evilone wrote:Just a F.Y.I for anyone planning on running a 50mm Taiwan bore.

Are you able to tell us what brand of bore you are using? Taiwan products are generally very high quality, and I've never had any quality issues. My Ruima 50mm BBK was perfectly set up right out of the box and has run without a hitch, nearly always WOT, for almost 10,000 miles. But I'd sure like to know if there's any low-quality merchandise out there, and who the maker is. I'm sure others here would like to know, too. Thanks!

Madman · Post by **Madman** » Fri May 11, 2012 5:13 am

Here is a picture before it was broken. But I don't think mine was too bad I think I broke it!!

Madman · Post by **Madman** » Fri May 11, 2012 6:27 am

bakaracer wrote:You have to check with a feeler gauge to make sure what the gap is at. But just by looking from your pic ,that looks like its more than enough. My guess is .013

We use mm here so it is 0.2mm
Converted to inches that is 0.0079

Madman · Post by **Madman** » Fri May 11, 2012 6:30 am

And piston clearance was 0.15mm or0.0059 inches if I'm measuring right!

evilone · Post by **evilone** » Fri May 11, 2012 6:12 pm

JJ Joseph wrote:Are you able to tell us what brand of bore you are using?

Sorry , got it used so i do not know the brand.

paulpauly7 · Post by **paulpauly7** » Fri May 11, 2012 9:15 pm

the brand that madman has is MTRT i have the same kit sitting on my bench new in the box

bakaracer · Post by **bakaracer** » Sat May 12, 2012 4:21 pm

Madman wrote:And piston clearance was 0.15mm or0.0059 inches if I'm measuring right!

yeah thats a bit tight. you want more like .20mm or.23mm range.

evilone · Post by **evilone** » Sat May 12, 2012 8:20 pm

JJ Joseph wrote:
Are you able to tell us what brand of bore you are using?

JJ, i contacted previous owner about what brand the bore is...it is a Ruima.

Madman · Post by **Madman** » Mon May 14, 2012 5:09 am

bakaracer wrote:
Madman wrote:And piston clearance was 0.15mm or0.0059 inches if I'm measuring right!
yeah thats a bit tight. you want more like .20mm or.23mm range.

So when I hone it out and add a new piston it should be fine I guess.

evilone · Post by **evilone** » Tue May 15, 2012 9:12 pm

evilone wrote:piston to cylinder clearance was .002" (not too bad).

(not too bad)

After more inspection and actually thinking about the measurements i got, i see mine is tight!

madman...mine is about .102mm-.152mm (.004"-.006"), and that's after honing the cylinder.

Madman · Post by **Madman** » Wed May 16, 2012 10:22 am

evilone wrote:
evilone wrote:piston to cylinder clearance was .002" (not too bad).
(not too bad)

After more inspection and actually thinking about the measurements i got, i see mine is tight!

madman...mine is about .102mm-.152mm (.004"-.006"), and that's after honing the cylinder.

Yeah ok its good (or bad) to know that this is one thing that could be messing us up, I guess a good bit of honeing could bring this clearance back to within specs. But i have a new 50 mm piston on its way and it will be interesting to see the clearance with that piston! Is the bore tight or is the piston fat?

evilone · Post by **evilone** » Wed May 16, 2012 4:12 pm

bakaracer wrote:yeah thats a bit tight. you want more like .20mm or.23mm range.

I've been second guessing myself all day at work....bakaracer, why does it need to be .20mm - .23mm range?
That would be .008" to .009" when typically they are around .002" to .004"
That would mean madmans piston to cylinder wall clearance would be a little under .006" which is actually a little on the big side. Is it a Ruima thing or what?

bakaracer · Post by **bakaracer** » Wed May 16, 2012 6:57 pm

You can try it at .18mm if you want. Pretty much any cast iron taiwan bores are tight. That's why you hear a lot of guys seizing a new bore with not that many miles on it. Its a crap shoot that you will get one that's. Ok clearance wise and no issues. But majority of them are tight by about .0015 so a quick hone helps. Plus pretty much all the cast iron bore don't have chamfered ports so running a flex hone throught will massage the ports too so they don't act like a squeegee and scrap the oil off the piston. Those sharp edges on the ports can chip small pieces off and cause seizes too so running the flex hone eliminates that issue of happening. Brake hones only make those edges on ports even sharper or even chip them so don't use a brake hone also called stone hones.

Red Eft Performance · Post by **Red Eft Performance** » Wed May 16, 2012 9:51 pm

evilone wrote:
bakaracer wrote:yeah thats a bit tight. you want more like .20mm or.23mm range.
I've been second guessing myself all day at work....bakaracer, why does it need to be .20mm - .23mm range?
That would be .008" to .009" when typically they are around .002" to .004"
That would mean madmans piston to cylinder wall clearance would be a little under .006" which is actually a little on the big side. Is it a Ruima thing or what?

First off Evilone how are you getting your measurement? Are you measuring the same way madman is in the pic above?
You guys should be measuring at the bottom of the piston 90 degrees out from the piston pin on the skirt. That is typically the largest point on the piston. Its very hard to get a accurate measurement with a feeler gauge. Really not the best way to do this.

Baka would know better than I what the best clearances would be for these bores.

So with that said if you are measuring with a feeler gauge you have to take your measurement and Divide it by 2. cause you are pushing one side of the piston against the cylinder wall and you are actually measuring the gap of both sides. So if you take Bakas suggestion of .008" your clearance is actually .004"

I will admit .004" seems a bit big for a 50mm bore. But maybe thats what needed do to the low quality of these bores. Again Baka has alot of experience with this stuff.

bakaracer · Post by **bakaracer** » Wed May 16, 2012 9:56 pm

Thanks Keith! yes the measurement should be taken at the piston pin area or just below it. the top of the piston is smaller than the middle and skirt area as the piston is tappered.

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