Removing stuck cylinder on Express SR

[vintagegarage]

I am having trouble removing the cylinder on my 1981 Honda Express SR. The cylinder is stuck to the crankcase. From the looks of it, the cylinder may never have been removed since 1981. Before I ignore the Workshop manual which says clearly "Do not pry between the cylinder and crankcase or strike the fins", does anyone have a better way of loosening up a stuck to the crankcase cylinder?

[Wheelman-111]

Greetings:

Ah, paper impregnated with fossilized petroleum products can be a surprisingly strong adhesive. Maybe spray the case/cylinder gap with solvent like carb cleaner or even WD-40 and patience for an hour or two while an opening in the bond is dissolved. Firm grip on the fins, up-down, left-right wiggle and PULL! Use a rubber mallet to thwack near the base of the cylinder.

[MrJumps]

Mean grean, I s*** you not eats up grease like an champ and tears up gaskets and seals. Soak it in the stuff and wait not even 15 minutes and you can pluck it right off. Also pour gas into the cylinder staright gas and it will help soft up the gasket internally.

[vintagegarage]

Thanks Wheelman and Jumps.. much appreciated.. I'll let you know how it goes..

[kuromi]

Rubber mallet and gently tap around the top of the cylinder in all directions.

If you look between the fins, you may see parts that look stronger to take the rubber mallet blows.
Never pry off the barrel as it risks scoring the mating surface which can lead to air leaks and the like.

[benji]

Wd-40 does work when you let it soak in.

[vintagegarage]

I finally gave up and ignored the service manual and pried (lightly) between the block and the fins. The cylinder finally released with a "pop". I don't think I damaged the block, nor the fins though. The piston was badly scored from various seizes in the past, enough so the rings were stuck. I'm going to take the cylinder over to a nearby small engine machine shop to see if it can be saved. I have a new "B" piston, and it is only very slightly larger than the original piston, and I have a new set of standard rings. Hope the cylinder can be just honed to fit the B piston, but I expect I will have to source a larger piston and rings.. I'll know more this coming week.

[Wheelman-111]

Greetings:

If by "B" piston you mean "first oversize", honing will not be a good method to address the bore. A qualified Bore Shop must set the cylinder in a jig for a re-bore, which is a very precise way to enlarge the cylinder for a perfect fit to the new piston. If they know what they're doing, they will install a Torque Plate and torque the cylinder down with bolts before they lower the machine bit. This is because there are subtle alterations in shape between an uncompressed and compressed cylinder. Yes, it's that precise. Failing to proceed according to this method, your bike may fire up and run, but its durability will be compromised.

[vintagegarage]

I am not sure what B piston means.. all I know is I have one, and it is not much different than stock bore. I think "B" means only slightly larger than original, but not sure. I think it is intended to take stock bore rings. I've been unable to find anything on the web that defines what a B piston is.. it is mentioned in the service manual for the NX50 and also in the parts fiche, but that is as much as I know about it. The only other choice I see is a new .50 oversize piston from ebay, and .50 rings from Honda.

http://www.hondapartshouse.com/oemparts ... aft-piston


The workshop manual says some cylinders are stamped A and some are stamped B in the area near the exhaust port, and the implication is that the stamping is done at the factory. My cylinder has no stamp at the place where an A or B should be.

I hear you that honing won't be good enough.

[frank50e]

I bore cylinders for HD's daily and the advice above is dead on.The same shop you take it to can measure the bore taking scoring into consideration.You may need a second or even third over to get a good seal.

[noiseguy]

I am not sure what B piston means.. all I know is I have one, and it is not much different than stock bore. I think "B" means only slightly larger than original, but not sure. I think it is intended to take stock bore rings. I've been unable to find anything on the web that defines what a B piston is.. it is mentioned in the service manual for the NX50 and also in the parts fiche, but that is as much as I know about it. The only other choice I see is a new .50 oversize piston from ebay, and .50 rings from Honda.

B-size is a very subtle difference from stock. They'd literally make the cylinder at the factory, measure it, and fit either an A or B piston in it... so, maybe .001" oversize?

You're going to need to run down a true OS piston and rings if there's visible scoring, or find a complete jug/piston set to replace. Sorry.