I have a set of CTR .25mm oversized pistons, the machine shop have measured them and they are 81.20mm, I presume the the ".25mm oversize" is the size they should bore the cylinders to giving 81.25mm bore and 0.05mm clearance. Can anyone confirm? As Honda UK have not come back with an answer.

 

Mine were 81.23mm new, block was bored to 81.25mm. 5 Hundreths sounds pretty close to the service limit. My manual is home, I'll check.

 

Thanks, I was pretty sure they should be bored to 81.25, but the machining company said if they have the exact clearences they can bore each cylinder to match up exactly with any inconsistancies in the pistons.

 

The standard for your piston-cylinder wall clearance is 0.01-0.04mm's (0.0004-0.0016")... So you'll be fine with that... If you wanna be dead on I would have the cylinders bored to ~81.225mm's... That is assuming all your pistons are exactly 81.20mm's... Are you using a caliper or micrometer??? Peace

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Kataku2K3 &raquo;</TD></TR><TR><TD CLASS="quote">The standard for your piston-cylinder wall clearance is 0.01-0.04mm's (0.0004-0.0016")... So you'll be fine with that... If you wanna be dead on I would have the cylinders bored to ~81.225mm's... That is assuming all your pistons are exactly 81.20mm's... Are you using a caliper or micrometer??? Peace</TD></TR></TABLE>

So if I take the numbers the machanic has given me then the piston-cylinder clearance would be the difference in diameters 81.25 - 81.20 = 0.05 divided by 2 (because the piston-cylinder clearance is all the way round the piston) giving 0.025mm (if the figures that have been passed on are accurate) which is pretty much in the middle of the spec.

I don't know if they were using calipers or micrometer, and I got the the info 2nd hand (the whole build is being done by my usual mechanic but the machining is being done by a specialist shop)

I have passed the info on, the machine shop will bore each cylinder to allow for any diffeences on each piston i am told which is why they needed the clearance info to get the best match.

Thanks for the info

 

Sounds good, good luck with the motor when it's all finished... By the way what are your plans for headwork, tuning, etc.??? Latez

 

As the companies over here in the UK don't have any proved porting for the ITR head like Portflow etc do in the US it will not be ported. I'm not willing to risk a bad port job (I may sort out getting a head send to the US one day to have it done). The head is being cleaned and the ports will be polished and any imperfections taken out but that's it. The cams going in are TODA B with Toda springs and Portflow retainers, along with TODA cam gears.

The bottom end is being balanced with the flywheel, possibly clutch assembly too (is that possible?) The engine is being completely stripped and rebuilt with all new gaskets and bearings. Block and head are being chemically cleaned etc...

While I'm here I'd like to thank Mike at IPS Racing for all the above parts and advice.

Oh, tuning will be via PowerFC