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Discussion Starter · #1 ·
Hi guys!! been sneakin around here for little while. I acquired a 78 CX500.....once i get the title, i am going to do some work to get it back on the road. Until then, i'd like to pick your collective brains on some technical work.



This bike was parked in '92' "because of a valve issue"...has 36,000miles on it...that's all I know.



I've got it idling. haven't done a compression/leakdown test. BUT...the ol' hand over the carb trick tells me that there is VERY little vaccum on the left carb intake! The right side sucks very strong, left, very weak.



Adjusted the valve lash to spec, everything under the valve covers is very clean,doesn't appear to be discolored from excessive heat, tappet ends don't have much wear, tops of the stems look great. lots of oil getting to the top.



Question is....how much trouble is a ring job?? I'm thinking of just changing the rings, and adressing valve seats and seals while i'm in there.



Ialso thought about just changing the head, but getting another decent one is a crapshoot.....although I know where there are about 20 of these bikes and multiple motors in a scrap yard, getting ready to go to the crusher.(Wva)



If i can just yank the cylinder, change the rings without going any farthur, check the valves, this will be a cake job!! or am i just dreaming!!!???LOLOL!! thanks in advance!!
 

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You cant 'yank a cylnder' on these bikes I'm afraid

Only the heads

The cylinders are part of the main casting



I'd pull the head first and check the valves this will also allow you to take a look at the pistons and cylinder walls

If you wish to then remove the pistons, you'll have to remove the front cover and undo the

big ends and pull the pistons and rods out of the top.



36 thou sounds a bit soon to have to renew rings though



If its been laid up since 92 the lack of 'percieved' suction may be due to sticky carb pistons but sticking my hand over the inlet is not a method of diagnosis I'd have a lot of faith in.
 

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Not as much cake as you're thinking or should I say hoping.





What is the actual valve issue that the bike was parked for?





The rings and pistons seldom have any wear worth addressing.

Unless your rings are frozen to the piston they should be fine.





Compression is tested on a warmed up engine in case you don't know.



For a left side piston removal I believe the front cover has to come off and then the whole transmission behind it. If you cant disconnect and reconnect the spring in the rear then the rear cover has to come off.
 

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Do a proper compression test first! Warm engine, plugs out, full throttle, etc. If you find the left side low (as you suspect), squirt a bit of oil into the spark plug hole on the low side and repeat the compression test. If it comes up, then you are looking at a ring issue. If it stays the same (ar close to), then you are looking at a valve issue.
 

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Discussion Starter · #5 ·
"If its been laid up since 92 the lack of 'percieved' suction may be due to sticky carb pistons but sticking my hand over the inlet is not a method of diagnosis I'd have a lot of faith in."



INDEED!!LOLOLOL!!



carbs are good...gotta get some rebuild kits, but everything is moving freely....definately not the cause.



have no idea about "the valve problem".....spoke with the original owner and that was all he said....I have a feeling he took it to a shop, and that was what they told him.



I'm pretty happy pokin around an explosion engine!! the lack of vaccum on that cylinder points to rings or valves, adn if you guys are pretty confident about 36,000miles or more off a set of rings, I'm betting on valves....plus the fact that supposedly it was actually the original issue...suppposedly.



I'll yank the head off that side and have a looksee!!! hopefully I can just dress teh seats and be done with it....



are parts fairly available for these bikes???? I saw some other posts saying bearings were gone etc.



this should be a fun tinkering project....I'm used to OHC inline Fours, so this will be an entertaining diversion!!



thanks again for the help guys!! I do appreciate it!!!
 

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Some parts that never really need to get changed have disappeared from the dealers. Others are just fine.
 

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anything special I should know about yankin the head off the left side??? seemed pretty straight forward, but everything has it's little tricks!!
no,no tricks 6 bolts,walk in the park
 
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