CL77 Boring/Clearances

cbxmountainman · Post by **cbxmountainman** » Sat May 28, 2011 9:29 am

Fellow members: I just picked up a set of pistons/pins/rings for a 305 first oversized. The only Service Manual I have is for a CL72. I need to have my cylinders bored to fit so I can get it back on the rtoad. What should the piston to cylinder wall clearance be? I imagine tyhe ring end gap would be the same, but not sure on the piston clearance be. I have a shop who will bore it for me for $100.00 total. Good price? Been a long time since I've had any machine work done. Thanks for any/all help, info. Charlie cbxman@nc.net

davomoto · Post by **davomoto** » Sat May 28, 2011 9:53 am

Charlie,

Sorry I dropped the ball on this one! According to my Honda spec guide, the piston to cylinder clearance should be 0.01-0.03mm (0.0004-0.0012in). $100 is a good price to bore two holes. I have a shop that does my 305s for that price, but his machine won't do the 250s. Those cost me $130 at a different shop.

Davo

Cheburashka · Post by **Cheburashka** » Fri Sep 14, 2012 8:34 am

I'm installing oversize pistons (Thanks LM!!) and have been looking at figures for clearance. The ones listed in the above post seem odd to me. 4 ten-thousandths to 12 thousandths clearance? Can that possibly be right?

I want to make sure I'm getting the right size when I spend all my extra cash on having my cylinders bored out. Had a shop do an old BMW R-75 once and they bored it out too big, leaving me exactly where I started after the rebuild.

48lesco · Post by **48lesco** » Fri Sep 14, 2012 9:00 am

Davo's post is correct; .0004"-.0012" with .0023" being the service limit. In shop-talk that's 4-12 "tenths" and some shops will question that small a clearance on an air-cooled engine. Tell them they don't have to break the edge on the top of the cylinder either since your pistons will go in from the bottom. $100 is a good price.
-48

cbxmountainman · Post by **cbxmountainman** » Sat Sep 15, 2012 3:53 pm

Finally got around to get this done. I got the clearance several months ago so thanks to the informer. I found someone locally who bored my block for $50.00. Coming along slow but sure. Planning on having it running in the next month as have some last details to finish. Thanks for the help.
Charlie

Cheburashka · Post by **Cheburashka** » Sat Sep 22, 2012 10:28 am

My local machine shop strongly advised against going to .0004. He wanted to take it straight to .0012. Only shop in town, and he generally knows what he's doing. We compromised on .0008.

Is anyone actually getting theirs bored to .0004? Does it matter if you're using oversize?

48lesco · Post by **48lesco** » Sat Sep 22, 2012 12:38 pm

8 tenths is fine, and if you bore gage it, it will be +/- a couple of tenths anyhow. I have had them at .0004 with no Ill effects, but then I'm pretty careful about running them in for the first 100 miles (<6k rpm, change speeds, not too hot, etc.) Be sure to check your ring end gaps too. .008-.016" on the top two and .004-.012" on the oil ring.

Honda305.com Forum

CL77 Boring/Clearances

CL77 Boring/Clearances

Sorry to dredge up an old one.

Piston Clearance