Author Topic: 1969 Honda Cub 90 (CM91) - Almost Done (hopefully) (Read 16589 times)

CBJoe · « **Reply #25 on:** September 05, 2017, 02:41:30 PM »

Quote from: b52bombardier1 on September 05, 2017, 05:07:10 AM

On my ST90 engine with the high performance Dr ATV cam, I needed to up the size of the main jet to about a 76. It was running quite lean with the stock 68 main in it. Overall, that cam and the bigger main jet only gave me maybe 2 mph of an increase in top speed so don't expect miracles.

Rick

Not so worried about top end speed. Did you feel much of a difference in the torque or grunt at lower speeds?

b52bombardier1 · « **Reply #26 on:** September 05, 2017, 03:36:51 PM »

Maybe a slight difference. Would I install this cam again? No. The only reason I had it was that I won it in the CT90 / CT110 Tech Weekend raffle in southern California.

Rick

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CBJoe · « **Reply #27 on:** September 05, 2017, 04:39:06 PM »

Quote from: b52bombardier1 on September 05, 2017, 03:36:51 PM

Maybe a slight difference. Would I install this cam again? No. The only reason I had it was that I won it in the CT90 / CT110 Tech Weekend raffle in southern California.

Rick

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Cool...thanks for the feedback

RAFster122s · « **Reply #28 on:** September 06, 2017, 02:00:02 AM »

The DrATV cam will not give you much if any top end, it gives you more torque/power in lo-mid range. You will see it in hills or pulling away. Ramps of cam open earlier and rate of opening is different on intake and greater duration on cam for both intake and exhaust.

CBJoe · « **Reply #29 on:** September 16, 2017, 05:31:40 PM »

Got the harness and connections all cleaned up and working. New 6V battery and replaced all the corroded bullet terminals.

Looking like I need to get a new left hand switch as the electrics are all corroded inside. Luckily they are readily available on eBay.

Muffler was rotted out but I found what looks to be a solid one that is on its way to me.

Getting ready to replace the tubes/tires/wheel bearing and brake shoes

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Gene · « **Reply #30 on:** September 16, 2017, 05:48:04 PM »

Very cool.

CBJoe · « **Reply #31 on:** September 17, 2017, 08:23:01 AM »

Can someone educate me on whether I need to worry about this on a bike that will not be doing over 60mph. There's a flat spot in the rim as you can see in the pic. Not terrible, but I don't think truing will get it out. The spokes at that point are finger loose now

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jgger · « **Reply #32 on:** September 17, 2017, 09:09:10 AM »

That looks like a pretty good flat spot, is it like that on both of the lips of the rim or just one side? In reality that bike will just be a short hop type of rider, I think that at 50MPH on a pristine new one of those you might have white knuckle syndrome.

It has, what, about 1 1/2 to 2 inches of suspension travel in the front?

Trace the curve of the rim on a piece of cardboard on a "good" spot and compare it to the flat spot to see just how bad it is, that might help with the decision to replace/run. You will not be able to true that out. If the bend is only on one lip you might be able to bash most of it out with a dead blow hammer or something.

You might be surprised as to how little run out is there at the tire after it is mounted also. The question is can you live with it?

You have enough going with the rest of the bike that you might just want to run it to see weather you can live with it or not. If you decide to run it make sure the spoke ends at the end don't stick out inside the rim enough to puncture the tube.

CBJoe · « **Reply #33 on:** September 17, 2017, 09:13:04 AM »

Quote from: jgger on September 17, 2017, 09:09:10 AM

That looks like a pretty good flat spot, is it like that on both of the lips of the rim or just one side? In reality that bike will just be a short hop type of rider, I think that at 50MPH on a pristine new one of those you might have white knuckle syndrome. It has, what, about 1 1/2 to 2 inches of suspension travel in the front?

Trace the curve of the rim on a piece of cardboard on a "good" spot and compare it to the flat spot to see just how bad it is, that might help with the decision to replace/run. You will not be able to true that out. If the bend is only on one lip you might be able to bash most of it out with a dead blow hammer or something. You might be surprised as to how little run out is there at the tire after it is mounted also. The question is can you live with it?

You have enough going with the rest of the bike that you might just want to run it to see weather you can live with it or not. If you decide to run it make sure the spoke ends at the end don't stick out inside the rim enough to puncture the tube.

Well...I guess it's a moot point. Its bent just enough that even with the spoke nipple tightened all the way the spokes in that area are still loose. I found a set of NEW original DID rims for a good price so I went ahead and ordered them and a spoke set. At least now the rims will be pretty

Joe

jgger · « **Reply #34 on:** September 17, 2017, 09:19:12 AM »

Well the upside is you now have something to make a nice wall clock out of. Haha

CBJoe · « **Reply #35 on:** September 28, 2017, 08:17:15 PM »

Hubs bead blasted and a couple coats of Eastwood Diamond Clear....new rims and spokes. First time lacing wheels...was a learning experience. Rear done...front soon. Waiting for some parts to arrive but should be running in the next couple weeks!

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CBJoe · « **Reply #36 on:** April 02, 2018, 07:14:41 PM »

The Garage is warming up again and it’s time to get this old 90 going.

Rebuilt some NOS D.I.D rims and blasted/rebuilt the hubs and sprocket carrier with new parts.

Got a bunch of miscellaneous nuts/boots/gaskets to get it refreshed.

Found a repro fairing as the old one was cracked and brittle. Also was happy to find an old dealer takeoff gas tank

. Doesn’t look like fuel has ever touched the inside!

Hoping to get it running pretty in the next month or so... exhaust is going to be fun...it’s an old one piece unit that’s pretty much unobtainable. I found one with a solid muffler and a bashed head pipe. My original is the opposite, so i’ll probably try and have them cut and turned into a single good unit.

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MoMo · « **Reply #37 on:** April 02, 2018, 09:43:36 PM »

starting to take shape, looking good...Larry

CBJoe · « **Reply #38 on:** May 27, 2018, 03:51:13 PM »

Getting close to having the cub running. The Carb was a real pain to figure out due to the specific flange spacing of this one off model. Essentially the engine side flange spacing is around 50mm and the carb flange was 46mm. However almost all C90s and all of the aftermarket carbs were 48mm. It was also made more difficult because of the backbone of the frame interfering with the aftermarket carbs.

FINALLY I found out there was some UK model from the early 80's that used the same flange spacing at the engine but had 48mm at the carb. Wohoo! It also has a slight twist which allows the carb to clear the frame.

EDIT: Adding info

As a follow up I can confirm that the following intake manifold worked well on my CM91 to mount a Mikuni VM19 carb with the 48mm carb flange spacing. The pipe also has a very slight twist in in which allows the Throttle cap on the carb to clear the backbone of the frame. NO interference or other issues seen.

17111-096-010 Pipe, Inlet that is marked for a C90 England (https://www.cmsnl.com/honda-c90-cub-eng ... ml#results)

I mounted a Mikuni VM19 and did an inline valve.

I got the rest of the engine gaskets needed and will mount all next week. Then hopefully one less project of the list

CBJoe · « **Reply #39 on:** June 04, 2018, 11:57:45 AM »

First start up with new Carb setup and all the engine bits back on. No muffler as of yet. Even with no muffler the bike sounds great and starts easy.

https://photos.app.goo.gl/NikLQOqTIlkAcZt92

The Exhaust System on this bike was a one piece unit. I have a good Header pipe and a good muffler...but I need to find a 25mm ID coupler to attach them. Cant seem to find one that with that small of an ID.

jgger · « **Reply #40 on:** June 04, 2018, 12:00:13 PM »

High performance go kart shops, maybe?

CBJoe · « **Reply #41 on:** June 04, 2018, 12:38:34 PM »

Quote from: jgger on June 04, 2018, 12:00:13 PM

High performance go kart shops, maybe?

Funny enough I was just thinking that....going to look to see what scooter shops are in the area as well. But they are all closed today.

CBJoe · « **Reply #42 on:** June 04, 2018, 01:54:54 PM »

Success! Was looking on some random forum and found this stuff linked

https://www.napaonline.com/en/search?text=exhaust%2Bflex%2Btubing&q=N%3D109532200%26Nty%3D1%26Ntk%3DKeyword%26Ntt%3Dexhaust%2Bflex%2Btubing&isProduct=true&indices=PIA

This stuff is perfect. I cut the Bad Pipe off the good muffler and did the same for the other. Did a quick test fit and it will work great! I need to get some cleaner clamps and ream the small flex piece, but I think with some exhaust sealant it will work nicely.

CBJoe · « **Reply #43 on:** July 07, 2018, 11:24:25 AM »

2 steps forward one step back. The motor starts up and runs great, but it was burning quite a lot of oil. Very Oily Spark Plug. So off comes the head. Whats funny is it looks so clean I wonder if someone rebuilt it before I got it and didn't run it much.

Also...I looked and looked disbelieving my eyes because there was no sign of a head gasket! However I'm not sure if that's the source of the oil in the cylinder?

Sorry if this is a dumb question...but would a missing head gasket on this 90 be the source of oil in the cylinder? Wouldn't that just cause poor compression?

Joe

CBJoe · « **Reply #44 on:** July 07, 2018, 11:47:05 AM »

Quote from: CBJoe on July 07, 2018, 11:24:25 AM

2 steps forward one step back. The motor starts up and runs great, but it was burning quite a lot of oil. Very Oily Spark Plug. So off comes the head. Whats funny is it looks so clean I wonder if someone rebuilt it before I got it and didn't run it much.

Also...I looked and looked disbelieving my eyes because there was no sign of a head gasket! However I'm not sure if that's the source of the oil in the cylinder?

Sorry if this is a dumb question...but would a missing head gasket on this 90 be the source of oil in the cylinder? Wouldn't that just cause poor compression?

Joe

Upon closer inspection I think I have my answer. The cam chain channel gasket was bent (see picture) and it looks like oil was leaking between the cam channel and the mating surface between the head and the cylinder. The piston and cylinder bore look near perfect.

I've got all new Honda OEM gaskets so I think I'm just gonna put it all back together (with a head gasket this time

) and see how it does.

Joe

CBJoe · « **Reply #45 on:** June 22, 2019, 07:00:35 PM »

Starting back into this project as it sat all winter. Poor thing starts up like a champ, but blows smoke like crazy. I didn't really check the valves/guides or anyting when I had it apart last. I just replaced the gaskets.

Just ordered the pieces to do a valve job on it. Should be pretty easy. Even ordered new guides.

scottly · « **Reply #46 on:** June 23, 2019, 09:40:17 PM »

That looks like way too much smoke for valve guides. I would look at the piston rings..

CBJoe · « **Reply #47 on:** June 24, 2019, 01:37:14 PM »

Quote from: scottly on June 23, 2019, 09:40:17 PM

That looks like way too much smoke for valve guides. I would look at the piston rings..

Thanks Scott...that’s on the list as well. Just need to pull the cylinder to see if it needs standard or oversized at this point

Plug is super wet with oil. But it starts like a champ

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CBJoe · « **Reply #48 on:** June 29, 2019, 12:39:55 PM »

Pretty sure I found the primary culprit. I pulled the top end off and removed the valves to inspect. Looks like some pieces were missing / incorrect.

If you look at the attached diagram...my exhaust valve was missing #'s 8, 9 and 14. So no ex valve stem seal or cap. I also found that whoever was in here last put the stem seal only on the intake valve...which is not supposed to have a seal.

Now I'm trying to decide what to do...I have all new springs, valves, guides, etc...I either just slap it back together with correct seal and pieces on the exhaust valve or take it in for a full refresh. The valves have a little bit of play in the guides...but I don't know if its too much.

Joe

RAFster122s · « **Reply #49 on:** June 29, 2019, 04:57:35 PM »

Some 90 motors did not have exhaust seals. The early S90 motors did not. So, be certain you have the correct exploded diagram and it does not source the seals for later serial number motors...

Can you put a dial gauge on the valves together a number on how much play. Odds are they could used replaced. Do you have the hones needed for the guides after being pressed in?
It is my understanding they would need honed to fit after replacement. Sounds like a full valve job would be needed and you apparently have most of it already...
If you intend to hang on to the bike, then doing a full valve job would be the way to go...

It is heartbreaking to find shoddy work that could have been easily done correctly for a few dollars more invested. DrATV.com is a good source of parts if you were not aware... Beatrice Cycles is their company name.

At least the small singles are easy to work on and most parts are cheap.
I have a 11/69 build S90 that was an Airman's bike, has a vin plate on the headstock, very rare to unheard of as far as S90s go...
Then a '81 C70 Passport that is very tired and sunbaked...
David

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Author Topic: 1969 Honda Cub 90 (CM91) - Almost Done (hopefully) (Read 16589 times)