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SOHC.co.uk Forums => CB750 => Topic started by: leadnavel on February 23, 2018, 11:22:32 AM

Title: Would you use these piston rings?
Post by: leadnavel on February 23, 2018, 11:22:32 AM: Hi guys your help would be appreciated with this dilemma. I'm continuing with my first 750 K7 engine rebuild, 32 yrs after removing the engine from the frame. The engine has been sitting without oil in it for all this time but I have been sticking some oil into any open engine holes over this period and hand cranking it to keep things moving. I'm in the process of stripping and cleaning the oily rust from the exposed surfaces and am unsure if would be OK to use the old piston rings as they have various markings on them, are these markings/stains normal. Although they look iffy all the rings feel smooth to the touch! What do you guys think?
Title: Re: Would you use these piston rings?
Post by: JamesH on February 23, 2018, 11:50:23 AM: False economy in my opinion...just source new ones...you'll always have a nagging doubt otherwise...
Title: Re: Would you use these piston rings?
Post by: Trigger on February 23, 2018, 12:09:21 PM: The piston to bore clearance needs to be tight on these old girls and as James stated, only muppets use old rings. You need to check that the bores are within spec and if they are, then they will need a light cross hatch and new rings, to insure that the engine will not burn oil ;)
Title: Re: Would you use these piston rings?
Post by: hairygit on February 23, 2018, 12:23:14 PM: And a set of rings isn't much more than a decent top end gasket set, which you would have to buy in the near future if you used the old ones!

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Title: Re: Would you use these piston rings?
Post by: leadnavel on February 24, 2018, 01:32:08 PM: Thanks for the information chaps, sounds like it would be a wise move to get myself a full set of rings to be on the safe side. I’ve miked and measured most of the other gubbins in the top end and all appears (surprisingly after all this time) to be within spec and in good nick, after a good clean. I haven’t got a bore gauge so next stop local mech to have the bores measured and cross hatched if needed. Much appreciated your wisdom is!

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Title: Re: Would you use these piston rings?
Post by: Tomb on February 24, 2018, 01:59:12 PM: I would fit the rings to the bores at the top of the bore wear area, and check the end gaps, if they're to spec and the rings look Ok everywhere else I would use them.
Title: Re: Would you use these piston rings?
Post by: haynes66 on February 24, 2018, 06:20:58 PM: i wouldnt. sometimes, rings lose their springiness. even if the end gaps are spot on, they may not push against the bore as they should. anything springy which has been unused, under tension for 30-40 years or more can 'settle' into their compressed position. well, it does with tractor parts anyway! dont know about japanese steel...
Title: Re: Would you use these piston rings?
Post by: mickwinf on February 28, 2018, 04:47:38 PM: as its an engine out job on the 750 would be a big risk, i might chance it on a 550 as can be done in the frame.