Author Topic: 1969 Honda Cub 90 (CM91) - Blowing Smoke  (Read 3343 times)

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Offline CBJoe

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Re: 1969 Honda Cub 90 (CM91) - Blowing Smoke
« Reply #50 on: June 29, 2019, 06:49:13 pm »
Hey David,

Yes indeed...that diagram is for the 1966 CM91.

I do not have the tools for doing the guides myself...I will likely take to a machine shop

We’ll see...it so easy to put back together I may just slap the seal and springs in and see what it goes. If still smokes I’ll take it down and do it all.

Joe



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Offline CBJoe

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Re: 1969 Honda Cub 90 (CM91) - Blowing Smoke
« Reply #51 on: July 01, 2019, 07:07:35 am »
Took the pieces over to Rons (MCRider) place Sunday while we were wrenching on his projects.  Overall feeling is that there's too much play in the guides and the cylinder shows some sign of needing bored/honed.

So I'm just gonna take it in to have the proper work done before putting back together.  Hopefully drop it off to a machine shop this week.  Just need to find one local that has a good rep.

Joe
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Offline RAF122S

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Re: 1969 Honda Cub 90 (CM91) - Blowing Smoke
« Reply #52 on: July 01, 2019, 10:34:54 am »
Small bores challenge many machine shops, may need to find a mower repair shop that does machine work.
I figured if you could feel play in the guides you would need them replaced...
Hope you can find a good shop to do the work.
David
David stuck in the curvy back roads of "Upper East" TN

Offline CBJoe

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Re: 1969 Honda Cub 90 (CM91) - Blowing Smoke
« Reply #53 on: July 01, 2019, 03:28:20 pm »
Small bores challenge many machine shops, may need to find a mower repair shop that does machine work.
I figured if you could feel play in the guides you would need them replaced...
Hope you can find a good shop to do the work.
David

Thanks David :)  I've got a call into once place and am reaching out to the local community to see who has a good rep for this small engine work.

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Offline CBJoe

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Re: 1969 Honda Cub 90 (CM91) - Blowing Smoke
« Reply #54 on: July 02, 2019, 09:43:14 pm »
Found a gentleman locally to do the machining.  He did a check before I left and determined that a .50 over Piston and rings are needed.  I've ordered the parts and will drop them off after they come in.  The old 90 will ride again soon...hopefully with less smoke  ;D

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Offline scottly

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Re: 1969 Honda Cub 90 (CM91) - Blowing Smoke
« Reply #55 on: July 02, 2019, 09:51:42 pm »
 ;)
Don't fix it if it ain't broke!
Helmets save brains. Always wear one and ride like everyone is trying to kill you....

Offline CBJoe

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Re: 1969 Honda Cub 90 (CM91) - Blowing Smoke
« Reply #56 on: July 02, 2019, 09:56:39 pm »
;)

You called it on the rings...guides were also shot.  Poor thing deserves a refresh


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Offline scottly

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Re: 1969 Honda Cub 90 (CM91) - Blowing Smoke
« Reply #57 on: July 02, 2019, 10:16:09 pm »
Smoke from guides can vary with load, but smoke from rings is more or less continuous, and heavier.
Don't fix it if it ain't broke!
Helmets save brains. Always wear one and ride like everyone is trying to kill you....

Offline RAF122S

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Re: 1969 Honda Cub 90 (CM91) - Blowing Smoke
« Reply #58 on: July 03, 2019, 01:13:18 am »
Joe,glad you found a place and he gave you the size for the piston and rings. He sounds like a good guy.

David
David stuck in the curvy back roads of "Upper East" TN

Offline CBJoe

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Re: 1969 Honda Cub 90 (CM91) - Blowing Smoke
« Reply #59 on: July 10, 2019, 02:37:35 pm »
Joe,glad you found a place and he gave you the size for the piston and rings. He sounds like a good guy.

David

His shop is like my retirement heaven..all full of machining tools and disassembled engines.  When I "retire" from my professional job (hopefully by 55 or before  ;D) I'll probably look to volunteer my time at a shop like this to learn some of the trade.

.5 Over Piston and rings dropped off today to him.  Will have new guides, valves, and cylinder bore all done.   Should be like new!

Joe
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Offline RAF122S

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Re: 1969 Honda Cub 90 (CM91) - Blowing Smoke
« Reply #60 on: July 10, 2019, 08:05:38 pm »
Do not forget to replace the can chain roller as they can disintegrate after sitting with a lot of age on them. They grow hard and then chunk apart.
Did you measure the camchainto see if it is in serviceable limits?
I do not recommend aftermarket rollers...guys on C70 and S90 have been bitten by some of them.


Congrats on the parts arrival and soon to be reassembled and running bike.
David stuck in the curvy back roads of "Upper East" TN

Offline CBJoe

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Re: 1969 Honda Cub 90 (CM91) - Blowing Smoke
« Reply #61 on: July 11, 2019, 05:02:00 am »
It has the DrATV performance cam, so all good there.

I'll look into the roller
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Offline CBJoe

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1969 Honda Cub 90 (CM91) - Blowing Smoke
« Reply #62 on: July 17, 2019, 11:09:10 am »
Got the head and cylinder back from the machine shop.  .5 over Bore Piston and Rings.  New Valve Guides installed, new valves and seats cut and lapped. 

Looks like new! Gonna put it back together tonight with all new springs and should be running again soon. Hopefully with no smoke :)



« Last Edit: July 17, 2019, 11:11:38 am by CBJoe »
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Offline CBJoe

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Re: 1969 Honda Cub 90 (CM91) - Blowing Smoke
« Reply #63 on: July 17, 2019, 04:28:43 pm »
Phew....that up close picture of the cylinder made me realize how dirty it is.  I did some blasting and evaporust soaks to clean it up today and I'll paint it tomorrow or the next.
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Offline RAF122S

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Re: 1969 Honda Cub 90 (CM91) - Blowing Smoke
« Reply #64 on: July 17, 2019, 11:01:03 pm »
Yeah, that cylinder looked a little rough on the outside. Glad you decided to clean it hip and repaint it. With it disassembled is the best time for that job...

Look forward to seeing it back together!  You are going to share some pics aren't you?

David
David stuck in the curvy back roads of "Upper East" TN

Offline CBJoe

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Re: 1969 Honda Cub 90 (CM91) - Blowing Smoke
« Reply #65 on: July 18, 2019, 02:35:27 pm »
Hi David..for sure I'll have pics.  Cylinder is all cleaned up and ready for paint.  Its super hot and humid outside right now though so probably wait till this weekend to paint it.

Joe
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Offline RAF122S

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Re: 1969 Honda Cub 90 (CM91) - Blowing Smoke
« Reply #66 on: July 18, 2019, 02:43:03 pm »
Good luck finding low humidity in July, at least here that is true...running 60-70% humidity here.

Look forward to seeing photos...

David
David stuck in the curvy back roads of "Upper East" TN

 

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