Topic: cb550 605 kit cylinder-piston clearance?

[francis8766]

I had my cb550 rebored and honed for the 605 kit amd had them installed. After i ran the bike, the bike wont hot start and it gets vdry hard to kick start as if the pistons aree stuck or something. Im thinking maybe the shop didnt leave enough cylinder-piston clearance to compensate when the piston swells when it gets hot. .

I would really appreciate your help regarding the proper cylnder-pistom clearance for the cruzinimage 605 kit. Thanks alot

I dont think the pistons are forged. Hope this helps

[francis8766]

Hey cal, ive been searchimg for answers from old threads and i found different answers. . So for these are the answers i found,,

Cylinder-pistom clearance:
 0.025-0.035
0.0028
.0012-.0015-.0020

To be honest, i dont even know if its the piston-cylinder clearance thats causing my problem. . Im really at a loss here. . Would really appreciate your suggestn on this. .




                                               

[bwaller]

Just another possible option is too little ring end gap??

[FunJimmy]

It matters not whether they are forged or cast pistons, only the material. Stock clearances are sufficient, or you could go up to as much as 0.0020

Cal,

It matters greatly. Forged pistons expand more than cast. Cast pistons can be set at 0.002" while forged will need to be closer to 0.0035", but check with the manufacturer first.

[FunJimmy]

Ya, I read that too Cal. There are quite a few "Forged vs Cast" discussions out there that are interesting to read. Seems it's not as simple as first believed. Alloy mix, skirt design, and more all have an impact and need to be considered when specifying clearences. Air cooled vs water cooled also plays a roll in piston clearences. I've stuck a few J&E forged pistons in air cooled Buell engines over the years and it gets expensive fast. Wiesco makes good pistons. I'd probably give them a try next time I do the top end.

[francis8766]

Hey cal. I think the too much friction for the motor to spin or kick over fits the description well. When the engine dies, i cant even kick it all the way down. . The engine wont quit on me if i wont let go of the throttle or rather the engine keeps going if i keep the throttle a little open but when the engine is cold, it will idle for sometime before it dies. The engine starts easy when its cold and can restart it after. The only problem is after running the bike for a few kilometers or maybe when the engine really gets hot

[francis8766]

Does too little ring end gap have the same symptom as mine? Because i didnt check my ring end gap before installing it. . What should the ring end gap be? Thanks alot guys

[francis8766]

Im also using 20w-40 motor oil

[alacrity]

Ring end gap is perhaps even more critical than a thousandths either way in piston diameter. Why? Because if the ring ends touch when compressed, they will break and your nice new engine will be farked.   If they are too far apart, it means they won't seal well (or at all) as the slide along the cyl wall.  It's the RINGS that hold your compression where it is supposed to be and your oil where it's supposed to be.  One should never trust an aftermarket supplier's ring sizing/gapping. it's super easy to check and way too important if they had an error in production and get it wrong.

[FunJimmy]

Does too little ring end gap have the same symptom as mine? Because i didnt check my ring end gap before installing it. . What should the ring end gap be? Thanks alot guys

Quite simply, they bind. If the ring end gap is to small it will close causing the rings to bind in the cylinders due to expansion of the rings as they heat. There should be a ring end gap specification in the shop manual. Alternatively, too much ring end gap will provide a route for combustion gasses to pass by the rings, reducing force on the piston (power) and contributing to blow by.

[Bootsey]

This is something I had wondered about... Are the desired ring gap specs still the same as stock size specs, even when using oversized pistons and rings?

[FunJimmy]

This is something I had wondered about... Are the desired ring gap specs still the same as stock size specs, even when using oversized pistons and rings?

Yes. The difference between overbore specs is nothing to worry about.
Ring end gap has to be sufficient to prevent binding in all temperature ranges and isn't precisely specific to the overbore.

[bwaller]

Those are cast pistons and it would be inexcusable to be too tight. Can't see a machine shop leaving less than 0.001" so likely not that.

Ring end gap of 0.004"/inch of bore so 0.010" bare minimum for compression rings. Since they're not OEM rings (even if they were) it's essential to check end gap.

Good luck.

[francis8766]

Hey guys, i just went to the machinist to have my cylinder checked and found out that they left less than 0.001 clearance. If i remember it correctly the machinist said he only left half of 0.001as clearance. . I hope this solves my problem. . Ill update as soon as i get my cylinder back and after the road test

[FunJimmy]

Did he mention WHY he arbitrarily pulled a half thou out of his a$$.
Any machinist worth his salt should know to ask what tolerance you want.
Get it fixed then rip his buisness card to shreds.

[alacrity]

I concur with funjimmy.  The ability to punch holes in metal does not qualify one as a "machinist."  From your description, you were ill-served by this hole-puncher.  I would doubt he used the proper jig to ensure those holes are perfectly aligned and "square" to the block and precisely centered in relation to each other so your conrods travel truly just as they did before your block was mutilated.   And based on his sloppy "half a thou/give or take" mindset, I would mistrust every aspect of the work  In fact, I would source a new cyl block and find an actual qualified pro machinist who will also be able to tell you if your formerly brand news pistons and rings are now farked and in need of replacement.  Get hole puncher to pay for it all--


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[Trad]

I had a similar but opposite situation with a local machine shop. They bored my cyclinder way too big for the JE 60mm pistons I had. Clearance called for from JE was something like .0028 and when I got everything back I mic'd the pistons and used my bore gauge to find out they were .0060 or more over!!!! I'm really glad I invested in those tools. I THEN PROCEEDED TO SEND MY HEAD AND JUGS TO MRieck FOR THE GOOD TREATMENT 

For your machinist to call out half a thou as clearance I call BS. I would take it to another shop and have them mic and gauge it all before you let the origional shop mess around some more. Just my 2 cents