Re-bore or Clean Up

[spookefoote1956]

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Hello again. I took the barrel of the wife's Cub today and saw the piston as in the attached pics. The barrel is clean and unmarked but as you can see the piston is well mucky. Should I just clean up the piston or is more radical work required?

Cheers, Chris

[g80csp11]

technically you should measure the bores and piston to check for wear , but in reality ne wrings and a deglaze of bore will get you more miles
why did you look , loss of power ? , burning oil, lack of compression etc..
Don't forget to do the head at the same time , grind in valves at very least


are the rings stuck in the grooves , if so you can get a few more miles by fitting new rings and cleaning

just cleaning and refitting will still you with the same problem

[spookefoote1956]

The bike has stood since 1995 and having finished the "Beast" it's now time to restore the cub so it was just a case of stripping it down to get casings vapour blasted etc. Everything was running fine in 1995. New rings would probably help a great deal.

[Rob Harknett]

Had to decoke a piston like that after about every 1/2,000 miles back in the 50's using that dirty old fuel. Please get in the habit of stuffing up the crank case before you let the piston out the bore. One day you may be pleased you did, when you lift a barrel clear and broken rings fall in the crank case. Also afterwards if you drop a ring circlip or something else goes down the hole.

[spookefoote1956]

Interesting what you say Rob. The last time the cub had fuel in her was before un-leaded. I'll be honest when I used to green lane her on the island she would put up one hell of a fight!

[Rob Harknett]

Thought perhaps it was some time ago since last decoke. I know I do fewer miles than when a bike was every day transport, but never had that much carbon build up. In fact the old decoke after x number of miles is now something seldom done. I'm sure all you need do is the usual clean up, grind in valves little perhaps, as already suggested, and all will be OK.

[Mick D]

Hi

I'm with Rob on this one:

From the photo it appears the rings are free and I can see no signs of scoring or seizure on the skirt, in view of this and your report of the barrel being fine I'd be tempted to just give it all a good clean up and re-lap the valves. Check the ring gaps on re-assembly but I wouldn't be too hasty in replacing unless absolutely necessary, if it was running fine before why mess with it?

Back in the days when de-cokes were a requirement I'm sure most of us didn't go any further than a good clean up, valve lap and inspection.

Regards Mick

[raffles]

One thing you should check on a Cub, is the alloy block on the oil pump which the pump drive spigot fits into they are known
to wear badly not allowing the pump full function
Tony

[Rob Harknett]

Hi

I'm with Rob on this one:

From the photo it appears the rings are free and I can see no signs of scoring or seizure on the skirt, in view of this and your report of the barrel being fine I'd be tempted to just give it all a good clean up and re-lap the valves. Check the ring gaps on re-assembly but I wouldn't be too hasty in replacing unless absolutely necessary, if it was running fine before why mess with it?

Back in the days when de-cokes were a requirement I'm sure most of us didn't go any further than a good clean up, valve lap and inspection.

Regards Mick

I would do the same Mick. All too often parts get replaced and prove to be no good. The old parts probably had enough life in them to last years, just using the old bike for pleasure.

[spookefoote1956]

Thanks for the advice, especially as the problem was not AJ related.