Topic: 350F cylinder ridge scraper

[sfhurst]

I recent acquired three 1972/3 350Fs in various states of completeness.  I am hoping to restore one to showroom stock and a cafe racer.  I have three engines that have good bores but a noticeable ridge at the top of each cylinder that needs removing.  All of the scrapers I have found on line are far to large for the 350F bore.  Does anyone make a scaper for small displacement engines?

[MauiK3]

https://www.jbtools.com/lisle-16000-small-cylinder-hone/?wi=off&gclid=EAIaIQobChMImpWP3cCf-wIVN2xvBB3CSQYAEAQYAiABEgJ7gPD_BwE

Not sure what size it accommodates but here is a start.
Welcome, keep us posted!

[Airborne 82nd]

I wonder if a brake wheel cyl. hone will knock it down? What is the diameter of the bores?

[Flyin900]

It is a good idea the check the bores for in spec tolerance if you haven't already, as the CB350F is critical for it being in spec. If you have a ridge at the top that isn't carbon build up then I would check the bore specs. There should be a copy of the FSM online here under the Manuals and Technical Documents near the top of the home page.

[sfhurst]

There is definitely a sight ridge of built-up carbon.  The bore is roughly 1.75" so the suggested tool would be perfect.  The carbon build-up is very thin, but very hard so I am pretty sure a hone won't touch it.  Yikes at the price of the JB tool but I have three engines to do.  I can always sell it on eBay after I'm finished for close to the purchase price.  Thanks to everyone for their help.

[RAFster122s]

If I recall discussions  about the cb350/360 and 400 motors they require extremely tight tolerances to prevent smoking on rebuild and have proper compression. Most automotive machine shops with no experience with these small motors ignore instructions and Do Not keep the tight tolerances required. As a result many of these rebuilt motors smoke and exceed the manual’s spec for rebuild. All because they are accustomed to car motors requiring much looser tolerances.

Not trying to be a killjoy, but be aware your efforts could be in vain or have a low success outcome.

HondaMan has talking about the tolerances and issues with the small motors. Drop him a PM and pick his brain a bit…

[Flyin900]

If I recall discussions  about the cb350/360 and 400 motors they require extremely tight tolerances to prevent smoking on rebuild and have proper compression. Most automotive machine shops with no experience with these small motors ignore instructions and Do Not keep the tight tolerances required. As a result many of these rebuilt motors smoke and exceed the manual’s spec for rebuild. All because they are accustomed to car motors requiring much looser tolerances.

Not trying to be a killjoy, but be aware your efforts could be in vain or have a low success outcome.

HondaMan has talking about the tolerances and issues with the small motors. Drop him a PM and pick his brain a bit…

As noted above if your not familiar with these motors don’t just dive in, the tolerances are critical and a simple honing can take a slightly worn bore out of spec.

[HondaMan]

I'm jumping in to echo the above comments: that ridge can stay there if the bores are otherwise not rusted. The pistons and rings will never touch it.

The piston-to-bore clearance in this little engine is 0.0004" (that is less than 1/2 of 1 thousandth of an inch!) and if the clearance becomes more than 0.0008" (that is STILL less than 1 thousandth of an inch...) the engine will both burn oil and weep it out the exhaust pipes.

Don't use 'bore scrapers" in this tiny engine (or any SOHC4, for that matter). If you feel the urge to remove that top crust of carbon, use a conventional brake cylinder hone, oiled profusely, and don't run it for more than 1 minute in any position in the bores. Otherwise, you're going to have to get bigger pistons and do it fully over with a proper bore job.

I get to fix lots of these...

[bryanj]

I agree, if it is a ridge you need a rebore and oversize piston kits done by a firm that knows what they are doing, there are lots of oil burning threads wherevthe rebore is not correct

[Tracksnblades1]

+3

Ridge reamers are for funnels…😩

[grcamna2]

subscribed

[sfhurst]

Just wanted to close this out by saying thanks for all of the advice.  Starting on engine #2 of three.  I'm sure this one will go much better.  I will use the whole experience in the Learning Curve class I teach.