Topic: CB350F full engine rebuild

[camshaft1991]

I’m starting this post as a complete rebuild of a CB350F engine and will stick to it until everything is done.

Most of the rebuild has been done already. The only problem I’ve had was: smoke, and idling on 3 cylinders. (Exhaust #4 warm to touch at idle)

The previous crankcase was damaged and replaced in a failed attempt to remove a broken tensioner bolt, but the rest of the components were salvaged. The replacement case was put together with new o-rings, gaskets, and solid bearings for the crankshaft and connecting rods. A fully rebuilt 400f starter clutch replaced the previous destroyed starter clutch. The oil pump has new gaskets and o-rings. The clutch is fully rebuilt with new plates and springs. The pistons are .5 OS. Camshaft is new along with refurbished rockers, and new timing chain components (except the timing cams on the crank and camshaft). On top of this I️ have a good set of carbs that can hold a reasonable vacuum when operating. 

I’ve rebuilt the engine to almost new, however, I️ have had the same problems now as I️ did before the rebuild: excessive continuous smoke, and idling on 3 cylinder.

The previous cylinder head was rebuild with new exhaust valves and refurbished intake valves. I️ ground them in by hand until I️ couldn’t hear the grinding compound anymore.

When the bike was ready to turn over, it ran the same as before only it had a significant loss of power, maxing at 3500 RPMs. I️ disassembled the engine two more times and once experimented with an improper copper gasket and then with a NOS gasket. Both failed but the copper gasket leaked oil. The cylinder head was bead and chemical blasted before the engine rebuild. I️ washed the head out with 8 gallons of distilled water, but I️ did degrease it with a hot detergent bath prior to sending it off for blasting.

I️ brought it to a shop and they told me I️ had to replace my cylinder head. With everything done so far, it made since. The spark advancer springs, and the electrical components related to engine firing time had been replaced as well.

With all that being said this is where I️ am now, a NOS CB350F cylinder head




It looks great but nothing is perfect after being shelved for over 40 years.

This piece is complete but it has some shelf wear on it and some.. blemishes that were never taken care of since it was made. The cylinder head base has some scratches on it that can be felt with a fingernail and there is no threads where the exhaust studs go in. I️ know where I️ can get that work done, as for the rest, could I️ correct this myself?



In these pictures there is: shelf wear, excess metal overhanging, scuffed flat surfaces, and leftover metal shavings when this block was cut. The contact surfaces on both sides of the head are flat.

What can I️ take away or make better without compromising anything? I️ have an air Dremel/ pneumatic rotary tool, various polishing and grinding attachments and an Emory Rouge kit. I️f I️ had someone do light deck work to my cylinder head base could they deck the top of it after I’m done grinding ridged edges?

I’ll keep to this thread after I️ get this cylinder head put together and resume engine build


Sent from my iPhone using Tapatalk

[ekpent]

 Sounds like your thread needs to get put over to the 'project shop' area if its going to be an ongoing thing.  Good Luck on it,another member here has done a lot of 350F work lately also,

[calj737]

Your other head very likely needed the valve guides replaced only, and maybe the piston-to-bore clearance was too big. You had better have the guides in this head checked VERY CAREFULLY before you go 1 step further.

Have a machine shop deck the underside of the head on a mill so it is truly flat and square. Do the same to the cylinder block. That will help solve leaks later. Once you assemble the head, turn it over and fill each chamber with fluid to insure the valves don't leak at the seats. If not, you're halfway there.

Those beauty marks you can very gently buff down. A Dremel will eat material very quickly, so use utmost care.

[camshaft1991]

I️ asked the guys at the shop about replacing the valve guides and they said that might fix it. Hearing that wasn’t too assuring. Also there would have to be more labor and new parts put into what ‘might’ work. My cylinder jugs were already milled with my previous head, would I️ need to do that again?

My head leaked when I️ experiment with copper but not too much with the NOS gasket, only when it was retorqued. When I️ relieved torque from the head oil seeped out from the front left corner. After retorquing oil would build on the front left corner a little.  It was acting like a worn cylinder head gasket but less leakage. And it probably would have gotten worse with time.

So with the “beauty” marks should I️ go with a hand file?
whats a good liquid to check for leakage?
Can I️ check the valve guides’ tolerances with an OEM Honda shop book and a vernier caliper?
And I’ll be sure to repost this to the “projects” section


Sent from my iPhone using Tapatalk

[markreimer]

Very curious how this pans out. I rebuilt my 350 top end three times now and it’s smoked like a chimney each time. First did a hone and rings, then a big bore, and then disassembled and rebuilt the big bore after crazy oil burning issues. There seem to be a lot of threads for failed 350F engine builds and not many successes.


Sent from my iPhone using Tapatalk

[camshaft1991]

I know right? It's daunting over me, but hopefully a fresh cylinder head will do the trick. By the way, how do move an entire post over to a different section? Someone told me how to do it a year or two ago but I cant seem find that post either.

[calj737]

The appearance flaws in your head are probably not going to be easy to remove in terms of getting the thing to look like a billet piece. You could do it, but at what cost? If you grind too far, too much, or weaken the wall structure, you're screwed. Send the head off to Nils @Restocycle and have to vapor blasted. That will produce the best looking finish, and knock back some of the casting flash.

Yes, verniers might tell the tale on the valve guides.
No, you don't need to deck the block again, but yes, do the head.
The pooling oil on the left corner is an interesting symptom...
SeaFoam works well on the leak test.

You can send a PM to a Moderator and they can move your thread  (Scott S will be happy to help you out)

[camshaft1991]

Just before i had the guys at the shop take the bike apart, I turned over the engine. They saw the smoke and each took turns grabbing exhaust #4. A few days later they gave me call when they finally had the time too look into my top end. They told me the the obvious: there is no combustion in the 4th chamber, but they couldn't figure out what was wrong. That it was spooked me.
Any issue the bike had before they were able to diagnose and fix, or I could if it was the carbs. They could confirm if I was right about something faulty or redirect me to what was really the issue at hand. They actually encourage me to do much of the work myself in order to save money on labor, but there shop isn't exactly one of those co-op shops for anyone to come and go. I think thats what they are called. I've come to an understanding after rebuilding my bike so many times that I need to hand it off to someone who has rebuilt 70s SOHC4s.

The gasket only started leaking when I relieved torque to the head for retorquing. It was like the oil was still under pressure and it came out as soon as the gasket was not under torque. I believe the oil that spilled out while I was retorquing prevented the gasket from sealing completely. I followed the retorque instructions by the Honda manual and used a digital torque wrench. Yes, I could of done something wrong but that is why I am having a shop take over, because I didn't have a second opinion or someone more knowledgable on hand. Not saying anything bad about the forum but it helps having someone actually there.

I think I will get a hold of Nills @Restocycle. The only thing I truly feel comfortable doing aesthetically to the engine is polishing and clear coating.

[innovativems]

I would send your head to mrieck on here.  He is the best person to go through the head and make sure it's perfect before you seal it back up. 

[calj737]

Your combustion issue with #4 could be as simple as the valves are whacked out of adjustment. Of course, the volume of oil tends to point towards guides, but you'll know soon enough.

I too would ship the head up to Mike Rieck (Boston area) after Nils vapor blasts it. In fact, have Nils ship it to Mike and save the shipping $.

[camshaft1991]

The problem with cylinder number 4 was always problem from the beginning even before the tear down. My first tear down was because of a broken tensioner bolt. If you are talking about valve gap I've always been on top of that ever since i had a valve tappet go loose while riding.. I had to replace the camshaft a rocker and refurbished the rest of the rockers. 

In theory if knock out blasting and milling with Nils and Mike (and assume mike can do valve work too for the sake of simplicity), could I polish the block with the valves in the block? If took the precautions of covering the orifices to the combustion chambers with tape and plastic cellophane/visqueen, could I safely polish without risking getting reside inside the chambers? I'm asking if anyone has polished a cylinder head with the valves in before.   

[calj737]

You certainly can polish the head with the valves in it, but you can simply drop the valves if you're that concerned. And yes, Mike is THE VALVE WORK guy. Milling the head is the "anyone can do it" machinist work.

[flatlander]

here ya go. no problem polishing covered up this way:

[camshaft1991]

awesome to both of ya!

[camshaft1991]

Alright I’m back at it. I mistakenly used the wrong o-rings for my carb fuel linkage, Hydrogenated Nitrile (HNBR), instead of Nitrile (Buna-N) o-rings. Long story short they started to dissolve and leak. So I instead of going with Buna-N I bought some Viton o-rings. Doesn’t hurt to get something slightly better.

Anyways when splitting my carbs I noticed this.

Aside from leaking, the carbs worked fine. This slide has got to go. I picked at the inside of the carb cylinder with my fingernail and found no rough edge to the wall. The bottom of the cylinder is a little bit chewed up in the last picture. I have an extra set of scrap carbs I can cannibalize a slide from, but I’m worried about the bottom of that carb cylinder. Will it mangle up the next slide I put in? Aside from replacing it is there anyway to fix this? Also I can’t use the corresponding carb on my other set because I believe it can’t hold a vacuum   


Sent from my iPhone using Tapatalk

[camshaft1991]

I replaced the damaged slide with one from my other carb set and fitted the viton o-rings for my fuel connectors.

They were a little tighter than Buna-N
o-rings but the fuel connectors fit snug. The replacement slide now glides quietly in the carb cylinder. Though it was slightly damaged at the bottom too, but superficial.

The return springs for these small four cylinder carb racks are wound pretty tight. I believe the slides get damaged from force of the return spring. So instead of letting go of the throttle, return it to idle by hand.

Here’s a page giving the just on several
O-rings. Pay no attention FFKM that’s overkill.  Probably made with infused depleted uranium and gold...


Stay away from HNBR O-Rings. The US standard is green. The color standards are different in other countries


My bike is still at a shop but I would hope my carbs would not leak anymore. I’ll leave them to tune it so I can get a good reference on how it should be tuned. Also I’m tired of lugging half a motorcycle across town via truck and trailer.


Sent from my iPhone using Tapatalk

[camshaft1991]

So far I have another 3 weeks before the bike shop can even look at my bike again and all that is left is to fit the carbs and boots on. The carbs are already assembled along with the engine but I think I can take over from here.
 Everything should be said and done. All I need to do is check the carbs for balance and retorque my head after a heat cycle. I read that the modern composite gasket does not need much retorque like vintage gaskets. So instead of backing out half a turn you check the torque values and tighten anything under what it should be. Is this true? Also should I do so with the engine still warm?


Sent from my iPhone using Tapatalk

[calj737]

if you have already torqued the head, then release the torque in reverse sequence, then torque it again. A heat cycle is not required.

Your notion of torquing them from where they are is flawed because you may encounter some that are loose, others that are not. Then you will end up with uneven torque values and a not flat head.

[camshaft1991]

Great so a gasket can be retorqued without a heat cycle. That’s a relief. The shop I went to assembled my engine and being a motorcycle shop I would assume they did retorqued it.


Sent from my iPhone using Tapatalk

[calj737]

Great so a gasket can be retorqued without a heat cycle. That’s a relief. The shop I went to assembled my engine and being a motorcycle shop I would assume they did retorqued it.

There's no issue with re-torquing most gaskets. You're not dislodging the gasket from its mating surface, you're simply tightening the nuts on the studs. We're talking 0.000x of measurement here. But that minimal measurement is important relative to other things.

[camshaft1991]

Good well now I have another tid bit problem, mounting the exhaust. The aftermarket pipes that came with the bike were pretty much plug and play, you could probably install them upside down if you didn’t know what your doing. I decided to go with 4into4 and they are quite a handful. Each pipe and muffler is a sing piece so no wiggle room. I’ve managed to install pipes 1,3, and 4 but 2 is catching on the kickstand. I even removed the kick stand and now it’s catching the mounting point for the kickstand on the frame.
And I tried staking washers in this last picture but not even close


Sent from my iPhone using Tapatalk

[carnivorous chicken]

Pipe #2 is supposed to go in between the side stand and the oil pan, not on the outside of the side stand... The side stand is between pipes 1 and 2.

[camshaft1991]

Or I could try riding like this lol


Sent from my iPhone using Tapatalk

[camshaft1991]

Ok I’ll try that but the spring for the kick stand would catch on pipe 1


Sent from my iPhone using Tapatalk

[carnivorous chicken]

Shouldn't.

If you google image 350F you'll see how the pipes mount, e.g.:
https://www.motorcycleclassics.com/classic-japanese-motorcycles/honda-cb350f-zmwz12jfzbea
There's some spce in between #1 and #2 pipes.