Just bought a 1971 CB350 with 1500 miles. What to do with the motor?

Wyld Bill

Been Around the Block
So as much as I love to fabricate and I love the old cafe style bikes I'm going to build a 100% OEM or at least mostly OEM looking bike. So I started with HondaTwins forum but seems pretty dead over there.
Motor questions-
Should I try to run the engine as is or tear it down and inspect inside, clean out old oil, replace seals & gaskets etc. Should replace the piston rings? Should I port the head or just leave it alone? (this isnt going to be a cafe bike)
Since I havent started on this project yet and its going ot sit for another week or two, should I drain the old nasty oil and dump in some degreasing solvent or gas or kerosene in the engine crankcase to loosen up the old oil crud?
Where can I get my engine bolts zinc plated or get new bolts that are triple zinc plated or something?
What paint should I use to paint the engine case? HIgh temp? What color for stock Honda?
Is there any sort of coating on the engine head or is it just raw aluminum?
If I polish any aluminum engine parts how do I keep them from dulling or oxidizing? Do you clear coat them?

Thanks
 
dude 1500 miles, run that shit!

do a compression check, and get it all running, if its pretty decent, might as well enjoy it while you can.
 
You're very likely to need new top end gaskets soon after getting it running, so you can do it now, or do it later. If you want to ride it first, it won't hurt things.
 
Its Winter in Maine so no need to ride right away.
Also I forgot to mention the kicker doesn't work so Ill need to pull the side case to see whats up with that anyways.
So if I'm pulling the heads to do the gaskets should I change the rings too since they are so old?
Also if I pull the motor it would be a good chance to clean it up and paint the base.
 
I would definitely pull the whole top end off. Typical on these bikes is the cam tensioner rubber disintegrating with lack of use, they get dried out and just fall apart. Rings should be replaced as well. you might find when you pull the heads that there is corrosion or oxidation above where the pistons ere stopped the longest. As well for the cost a carb kit should be installed. For the cos i would also take it to a carb specialist and have then carbs cleaned ultrasonically. Its really the only way to get all the small ports fully cleaned and smooth. Finally the rubber should be addressed. Old tires cn look good but just fall apart at 50mph all of a sudden.
 
Thanks Thecoffeguy. Do you think I should put anything in the lower unit for now to loosen up any old oil sludge?
Yeah my buddy wants me to just try to start it but I am also worried about crud or corrosion in the cylendars in particular up above the pistons.

How much is a carb rebuild kit and cam chain rubber and where should I buy them?
How about rings? Shouls I buy new old stock OEM or new non OEM ??
 
Bill
If you are going to drain the lower end later anyhow, you may slip a half liter of varsol in and slosh it around. I would first drain any liquid oil that comes out, then put the solvent in. once you have sloshed the solvent around a bit each day for a week or so, then drain it. Drain it for a long time. After a month or so of draining, put say half a quart of thin oil in and slosh that around, say a full 5 weight oil. That will thin out the solvent that might have remained in any of the smaller recesses, then drain that.

i buy carb kits from, http://www.siriusconinc.com/ they have reasonable priced ones and I have never had an issue with any products form them. They also have a lot of other cables and rubbers and seal etc.

The Cam part will probably only get from a dealer. Your local guy is a good resource. if you can find an old guy there he can give you a lot of help. All the Rings and stuff should either be new OEM or new old stock. Even after market if you find thema re fine. online i always search with the actual part number. this can usually be found on fiche at cmsl.com
 
Miles mean almost nothing at all.
The years have done more damage then anything. Honestly a bike that has been used and maintained that has a million miles might be better off then something sitting for 40 years doing nothing.

Blindly tearing it down is kinda stupid as well. Just spending money and doing work for the sake of work with no real light at the end of the tube.

Can't really tell anything untill you get the motor running and warmed up.
Motor needs to be hot for a compression test.

You have all the micrometers and other related engine rebuilding tools needed?
 
I only buy OEM Honda parts for the motor.
You can get 99% of things right at the dealer or dealers online
The aftermarket stuff like carb parts are generally wrong and poor quality. Also they are the same if not more money then the correct honda part.

You do have a factory manual right?
 
Honestly, I would have to agree with surffly. Don't cause yourself headache for no reason, spend your time on other areas of the bike first especially if it already runs without issue. Drive it till it breaks
 
Ok an update. It is pretty much siezed. I have a gasket kit on the way. I'll order some rings and the cam chain friction plate thing. I just pulled the carbs off and cleaned them last night. Not too bad I must say I've seen a lot worse. One problem though is the floats are destroyed. Anyone know if the floats from my 1981 CM400 carbs would work? It looks like they would be a nice upgrade,..that and the float needle valve. So will I need any special tools besides a valve spring compressor and a cylendar hone to pull the head off and go through that with new gaskets and seals? As far as the base I think I'll just flush it out, maybe pull the side case off and pull the clutch pack apart and clean or soak the friction plates, then put that back together.
Anything I need for parts besides a standard engine gasket kit, two piston ring sets, and new cam chain tensioner, and some new SS bolts and nuts?
 
TheCoffeeGuy said:
Bill
If you are going to drain the lower end later anyhow, you may slip a half liter of varsol in and slosh it around. I would first drain any liquid oil that comes out, then put the solvent in. once you have sloshed the solvent around a bit each day for a week or so, then drain it. Drain it for a long time. After a month or so of draining, put say half a quart of thin oil in and slosh that around, say a full 5 weight oil. That will thin out the solvent that might have remained in any of the smaller recesses, then drain that.

i buy carb kits from, http://www.siriusconinc.com/ they have reasonable priced ones and I have never had an issue with any products form them. They also have a lot of other cables and rubbers and seal etc.

The Cam part will probably only get from a dealer. Your local guy is a good resource. if you can find an old guy there he can give you a lot of help. All the Rings and stuff should either be new OEM or new old stock. Even after market if you find thema re fine. online i always search with the actual part number. this can usually be found on fiche at cmsl.com

Whats Varsol?? I was thinking someone would tell me some weird concoction that I dont have. I have gas, diesel, kerosense, degreasing solvent....none of those would work?
So,...if I buy an new, old stock cam tensioner would that be junk too??
 
Why are you ordering any parts without knowing whats wrong?
Maybe the motor just needs rings, maybe it needs to be bored out. You will have no idea till you measure everything.
There is no magic list of things you need.
 
Get the kick starter fixed and some good carbs and fire it up. You probably don't need rings. You don't need a bore. It will be fine.
 
Varsol is like paint Thinner. The problems with Diesel and kerosene and the like is their similarity to oil and their flammability. If its sludge you are after you need something that will break up and dissolve the crap that's there. Not sure about the Carbs. I sold my CM450 last year, it definitely had different floats. if they are identical of course you can swap them out. You need to be concerned about the level and volume of fuel in the bowl. that will determine if they are exchangeable and run and get tuned well.

Generally if it wont turn over, the pitons are stuck in the cylinders. This indicates one of two things, one the bike was seized for being overheated, in which case you will need new rings and pistons and have the cylinders honed. or two the pistons are oxidized to the cylinders and in which case you will need to have new rings and pistons and the cylinders honed. Not a big job and these bikes looks like crap running down the road spewing out blue smoke because the cylinders and pistons are crap. For a hundred bucks or so get it done. Its still December in Maine right?
 
Wow a wide array of responses. :eek:
I have the scanned in PDF FSM but maybe I'll order a Clymer manual on-line.
It feels like it wants to turn over when I put the bike in gear and push the bike but I don't want to force anything too much. The guy I bought it off said when he got it "It wasn't siezed" So I'm guessing there is rust on the cylendar walls, he tried to turn it over, now it is siezed. When I got there he had dumped some Marvel M oil in the spark plug holes.
As far as ordering part ahead of time, once I get something all torn apart I don't like to leave it sitting there all torn apart while I wait for parts to to show up. Once I start in I like to have everything I need right there ready to go so there is less risk of loosing parts, forgetting how stuff goes together, stuff getting dirty, etc. But I guess I could just take it apart then see what I need for sure.

So where do I purchase Varsol? Auto parts store like Napa?
 
surffly said:
Why are you ordering any parts without knowing whats wrong?
Maybe the motor just needs rings, maybe it needs to be bored out. You will have no idea till you measure everything.
There is no magic list of things you need.
What do I need to measure???
 
I buy it at the Home Depot. What I think he is talking about measuring is the piston bore after honing. While i have never seen over sized pistons, they may be available. there are however over sized rings. my recollections is they start at 10 Thou over and go up in increments of 5 or 10 thou. This will totally depend on what the inside of the cylinders is like and how much honing is done. you may have to take the honed pistons to a shop to measure inside diameter accurately. these instruments are expensive and there is no need o purchase one.
 
Most of the opinions have already been covered. If you want the motor to be as good as new then it will have to come apart and be cleaned, inspected and rebuilt. It's nice if you can do a compression and leakdown test first so you have a baseline, but not essential.

When I strip a motor I have a pile of different sized baking trays and plastic bags that I drop things into and a camera and notepad. Things that seem so obvious when parts are coming off are not always as obvious when trying to put them back together.

CB350 is a basic motor and no real tricks or specialty knowledge required. Once it's stripped, the bores and pistons will need to be examined and measured for wear. Measure valve spring length and compare to spec. Same with clutch plates.

Take your time and enjoy the journey. You will need a complete gasket set and seal kit, so go ahead and order those if you want, but you can't tell about bores and pistons until you get inside. The same goes with valves and springs etc.

My sequence is photograph and document. Remove engine and strip it. Clean parts a few at a time. Examine, inspect, measure, take notes and start a shopping list. Within a few hours/days/weeks I have parts ordered and can continue with closer inspection and refurbishing parts, painting, checking mating faces, cleaning out threads, removing raised metal when case screws are pulling it up and so on.

Send heads and barrels for machining once new pistons arrive. If the bores measure up OK but are rusty, have a local machine shop run a hone through the bores and check them again.

Repeat as required until parts are all perfect.

Pistons and rings typically come in .5mm O/S, 0.75 and 1.00. Some manufacturers used to sell 0.25mm but they are rare, and some popular models have all sorts of oversizes available. Forget about fitting oversized rings to stock bores and pistons, That's not a practical solution as a rule.

Build. Sit back and enjoy.
 
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