Author Topic: 1969 Honda Cub 90 (CM91) - Almost Done (hopefully) (Read 16591 times)

CBJoe · « **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

Sent from my iPhone using Tapatalk

CBJoe · « **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

RAFster122s · « **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

CBJoe · « **Reply #53 on:** July 01, 2019, 03:28:20 PM »

Quote from: RAF122S 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

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.

CBJoe · « **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

scottly · « **Reply #55 on:** July 02, 2019, 09:51:42 PM »

CBJoe · « **Reply #56 on:** July 02, 2019, 09:56:39 PM »

Quote from: scottly on July 02, 2019, 09:51:42 PM

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

Sent from my iPhone using Tapatalk

scottly · « **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.

RAFster122s · « **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

CBJoe · « **Reply #59 on:** July 10, 2019, 02:37:35 PM »

Quote from: RAF122S 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

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

) 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

RAFster122s · « **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.

CBJoe · « **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

CBJoe · « **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

CBJoe · « **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.

RAFster122s · « **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

CBJoe · « **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

RAFster122s · « **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

CBJoe · « **Reply #67 on:** July 23, 2019, 11:01:01 AM »

Top end done and installed. Battery charging now. Hopefully it starts later without too much trouble!

Sent from my iPhone using Tapatalk

CBJoe · « **Reply #68 on:** July 23, 2019, 12:03:36 PM »

It lives....and no more smoke. Currently no exhaust gasket installed, but have them on order. I need to take the throttle assembly off again as somethings hung up so it’s not operating properly. Once that’s cleared up I’ll mess when the carb tuning.

It’s got a VM19 aftermarket carb in it as I haven’t been able to find a stock carb. Heading out of town for till Sunday so will mess with it all when I get back. Nice to almost be done with it.

Sent from my iPhone using Tapatalk

RAFster122s · « **Reply #69 on:** July 23, 2019, 12:16:21 PM »

Very cool Joe! Congrats on the successful rebuild. Ride it like you stole it! Throttle assembly is finicky if like the S90. Might just need lubed. I would suspect it might be at the carb since that part was apart. Verify your carb piston is assembled into its slot correctly,but not having running issues it is low probability of being the cause.

CBJoe · « **Reply #70 on:** July 23, 2019, 12:35:38 PM »

Thanks David...rose is looking forward to learning to ride. Just need to get the details sorted and make sure it’s safe and then parking lot training begins

Sent from my iPhone using Tapatalk

CBJoe · « **Reply #71 on:** July 29, 2019, 03:46:51 PM »

Figured out my throttle issue. Didn't realize it but the aftermarket carb Top doesn't have a barrel adjuster to take up slack. So there was way too much free-play in the cable. Ordered a new Carb Top with Adjuster from DrAtv. Should take care of it.

Gene · « **Reply #72 on:** July 29, 2019, 05:30:28 PM »

I'm just happy you saved it.

CBJoe · « **Reply #73 on:** August 02, 2019, 02:52:01 PM »

Little 90 is running pretty well...shifting good and easily rockets along at 45mph on flat ground

Just takes a moment to get there!

I'm a little bummed because after it gets really good and warmed up, i've got a tiny bit of exhaust smoke

Doesn't smoke at all at startup, but after 10 minutes of riding I've got a little bit. Just put a brand new spark plug in before this ride. Heres a video of said smoke. I'm kind of worried I nicked the exhaust valve seal or something when I installed the valves and such. I have to admit that the tank has year old gas in it as well.

BTW...the pipe blued really bad the last time I ran it as I had the mixture screw turned way in and it was lean

After turning it off and back on, the smoke pretty much goes away. But i'm sure it would come back if I rev'ed it up.

Here’s the plug after about 15 minutes of riding. Thinking it may still be lean. Might put a slightly larger main in.

RAFster122s · « **Reply #74 on:** August 02, 2019, 10:55:27 PM »

Plug looks a bit lean.

Glad it is running well. Did you put the DrATV performance can in it?
Video definitely captures the clacking noise of the valve train.
Your rings aren't even broken in yet...let the jury stay out on the smoke.

News:

Author Topic: 1969 Honda Cub 90 (CM91) - Almost Done (hopefully) (Read 16591 times)