Topic: What is wrong with my 350F

[camshaft1991]

So I have a 72 CB350F that I recently gave up working on and gave it to a shop because I have no more time and its beyond my abilities to work on. The engine and carbs are fully rebuilt with: all new seals, all new bearings, cb400f starter clutch, rebuilt clutch (with original springs), new .5 pistons and rings, new cam chain, new cam chain boot along with other associated cam chain parts, new camshaft, new valves, NOS cylinder head, all new dowel pins, and all new socket engine bolts. I still have most of my original crank case studs in, but I'm not running a performance build. I'm trying to do a working build.

My problem with my bike is that it leaks oil outside of cylinder number 4 along with power loss and grey smoke. I was skeptical about my clutch so I let the shop look at themselves and put it back in. The smoking exhaust could be from improper synching of the carbs which something I can manage on my own; however, the oil coming out of the exhaust is unrelated to the carbs.

Prior to the engine rebuild it ran on 3 cylinders with air chocked out of cylinder number 4 through the carb. You could only synch 1-3 by choking air to 4. So I swapped out for another set of carbs and rebuilt them. I had a previous mechanic that worked on the bike who did everything right on the bike except for the carbs. He bored my cylinders out and I purchased a .5 piston set from cmsnl. The problem was is that he set the carbs too rich and the engine washed out. The gas in the combustion chambers washed out the oil inside. So I went with an actual shop who gave them a slight hone. There was hardly much of anything actually damaged, everything was within marginal standards. It still had faint hone markings and the piston ring gaps were still good.

We originally thought it was the cylinder head causing the oil leakage, performance loss, and smoke or the valve guides themselves. Instead of replacing the guides I went with a new old stock cylinder head with valve guides. No one knows why it's doing what it's doing. This second build is almost the same as the first build with the crapy mechanic. It has always leaked oil out of the exhaust and it leaks some around oil pan but that is unrelated to oil shooting out of the exhaust. The diagnosis now is to replace the cylinder rack and pistons. I used an OEM Honda workshop manual to choose the right bearings for my crank and conn rods. I also checked the crankshaft and case gap and the crankshaft and conn rod gap twice with Plastigauge sticks.

It's in the shop now but I am going to get more word from the mechanic assigned to my bike.

[Remcod]

Not stating this is the issue since you have done so much work on the engine, but a known issue with the cb350f is leaking oil seals of the oil canal dowl between head and cilinder. I replaced mine with aftermarket that leaked almost inmediately again. I then replaced with original and copper coated the cilinder head gasket that untill now has stopped the leak.

When i compared the original seal with the aftermarket, the aftermarket was slightly shorter that could be the issue.

[Bodi]

Well, the oil isn't coming through the carb. So we know something!
You don't have too many suspects.
- cracked or porous piston: unlikely.
- hole or crack in the head: also unlikely and I think you already swapped heads.
- terrible valveguide fit: possible but they would be a loose rattle fit to have oil dripping from the exhaust. Hard to miss.
- piston rings installed wrong: definite possibility, could move a LOT of oil into the chamber.
- head gasket leak: IMO most likely, since it is #4 ... the oil supply galleries up through the barrel section end at the flow control orifices at the outer ends of the head, a few mm from the 1 and 4 bores. The rubber seals are not excellent. Leaks to the outside or to the adjacent bore are common.

However, you seem to have had the head off or swapped and been in there a few times. Unless you gave a damaged barrel section or head I don't think the same leak woul persiat through several head gasket and orifice sesl changes.

I would check the rings first, if they are correct inspect the head gasket faces on barrel and head sections, valveguide fit, look for cracked guide or cylinder barrel ... magnaflux or dye test these?

Sealing the oil galleries and orifice valves is difficult. OEM orifice seals seem best, and head gasket thivkness is critical so using an OEM gasket is possibly best. Check and correct out of flat head and barrels.

[camshaft1991]

Thanks for the thorough responses. They haven’t got around to do a leak test and probably won’t have time to get to it until week after this week. I myself am leaving the country right now and I won’t have cell service until I return to the states Saturday.
The bike is acting similar to how it was prior to the head swap, so possible elimination?  Bout to loose signal but I’ll get back as soon as I can on this.


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[camshaft1991]

Alright, I've come to the point where I might just take my bike home do it myself and hope for the best. My local motorcycle mechanic shop or shop near my Dad's house, called today asking how to proceed.. I'm on good terms with the owner of the shop so he gave me the call. He gave me details from the mechanic assigned to my bike but it was almost the same from a brief conversation we had late December.
-Passed leak down test with soaring colors
-4-6% efficiency loss across all cylinders
-carbs unsynched
-black smoke continues to plume out of right exhaust (exhaust #4)
-too much oil pumped in? (guess work)


Going over what was suggested by Bodi: The cylinder head gasket was from a gasket set from 4into1. The gaskets for the two dowels and two oil control valves between the cylinder and head were purchased from Yamiya750. The dowels are all new, but the oil control valves are original. They should not be blocked because I have soaked them in acetone and have blown pressurized air through them several times (without soaking the gaskets). The owner of the shop said damaged rings could cause black smoke or oil to burn, but the leak down test would have failed. The head and cylinders are flat though they were not done together, but the previous head had similar symptoms and it was milled along side the cylinder rack. To see if I had improperly installed the head, I asked them to install and torque it. I remember when I installed it I had a slight oil leak at cylinder #1. I might have been obsessing, but I could have sworn i saw a bit of yellow oil underneath the grit of the Cue Tip I used to swab the compressed gasket.  When they installed it, it did not leak. However, they still came across the same problem after installation, it still bellowed out black smoke from exhaust #4.

Remcod: I have used spray on copper sealant before and I failed miserably. I did per instructions but I had a better seal without the spray. I used Permatex copper spray, but I didn't have someone else try to assemble my head with a copper coated gasket. And what I said before I bought dowel and oil valve gaskets from yamiya750, whom I've gathered sells quality gaskets and o-rings for old SOHC4s. 

I have come to the conclusion that the cylinder rack itself has not been ruled out. Piston are good, rings good, everything above and below good. I have not done a magnaflow test on the cylinder rack. Aside from the transmission, crankshaft, oil pump, oil filter case, oil pan components, alternator, crankcase covers, half the crankcase studs, cylinder rack, valve cover, breather cover, and oil pipes the engine is completely different from when I first bought the bike. Almost half the engine is brand new maybe more. The one thing that does have me on slight edge with the bike is the crankcase studs. I replaced half of them in the process of transferring them over to another crankcase, but I'm just doing a running build not performance (long story why.. i broke it). I also rebuilt the transmission with new cotter pins and thrust washers and the primary shaft has new rubber dampers and the crank and con rods have new bearings. And... I did choose the right bearings and never again will I do so for any engine.. I have to stop myself from listing all the reasons why it should work.

I'm eventually going to take it home within a couple of weeks, synch the carbs, and run the bike. It could be residual oil in the pipes from whenever oil leaked in them previously.. but they are new 4into4 headers.. Maybe actually riding it around could help, but I still don't know if it will run at full power after the carbs are synched. The carbs probably need a good soak. Lucky for me I can reuse the same jets, because I bought all their o-rings in bulk. They have only been in for less than 4 months. No sense on throwing away perfectly good jets over new o-rings. I also traded most of the Buna S (nitrile) o-rings for longer lasting Viton o-rings. Harder to work with but pay off in the long run.

If I were to disassemble my engine, should I flush all the remaining oil in the cylinder head oil galleys with spirits/acetone after draining the oil? If I did, I could remove the head without residual oil dripping/seeping onto the gasket after being detorqued and removed. And thus have a better reading of what my gasket is trying to tell me. I lost a torque wrench in a flood so I would need to get another one of those before even considering, and my Dad wouldn't be too happy again with me taking up space in his shop again.

If anyone has any breakthrough discovers on why CB350F engines bellow out black smoke even after several rebuilds, please let me know. This has to be one of the great mysteries of the world along with aliens and whether or not dead famous celebs are still alive somewhere hanging out together.

[calj737]

And if you pull the plugs from all cylinders, what do they look like? Is there presence of oil on any of them, or is the smoke related to fuel?

[camshaft1991]

I could get plugs 1-3 to just about any color. Plug four only comes in two flavors crispy or wet (gas). I could lean out or enrich the whole engine and plug four would be black. It’s not enough oil to stay on the plug. The plug has never felt oily. I know after tinkering with the bike while it’s running, my clothes will start to smell like burnt oil. But if the plug is not oily and the engine burns oil...
I feel I like I need to do more spark plug test again to believe it myself.


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[calj737]

Is it currently using oil? If the compression is good, leakdown is healthy, but plug is black and smoking, I’d start REALLY examining the ignition, coils and plugs/caps.

[scottly]

If anyone has any breakthrough discovers on why CB350F engines bellow out black smoke even after several rebuilds, please let me know.

Black smoke is caused by too much gas for the about of air, producing carbon. Burning oil has more of a bluish tint.

[HondaMan]

One thing I don't see mentioned here is vital in this engine, and there is another thing that will make it leak oil.

First thing: piston-to-bore clearance. If it is more than 0.0012" on a new bore, it will not seal. These small pistons are supposed to have 0.0004" (that's not a typo) clearance. When the clearance reaches 0.0020" the bores are considered to be worn out. Many machine shops that don't know this will treat these engines like a lawn mower and bore then for 0.002" from the get-go, rendering it impossible for the rings to seal the resulting massive flood of oil against them.

The other thing, which is common today with 100% of these bikes upon rebuild with modern head gaskets (i.e., made after 1996 or so): the head gaskets are all 20% thicker than OEM, so the O-rings that seal the oil passages to the head WILL leak oil, usually immediately. No MLS gasket will fix this, and any other sealing attempts only delays it. I get between 1-4 e-mails every month from someone who is struggling with this issue. It goes like this:

The modern head gaskets are typically 1.00 mm thick. The original design called for 0.80mm thick head gaskets. The O-rings that seal the 60 PSI oil passages to the head require at least 0.2mm of compression, plus metal base edge support, to seal this much pressure. So, to make them seal, you really have just one correct choice for a long-term fix, and a less correct choice for a short term fix: long-term means finding O-rings to replace the ones that came in the gasket set for those 2 oil passages and get some that are 0.2-0.4mm thicker. Make sure it still fits inside the recess in the cylinders where these live. This will give it metal support and will hold the shape of the O-ring inside the head gasket. The 'other' fix is to mill the cylinders far enough to remove their recesses altogether, which will work until the O-rings fatigue and crack in a couple of years, then the leak will return.

Seen this many, many times...on all Honda Fours and Twins...

[camshaft1991]

Huh.. that’s interesting on the clearance, I don’t think the feeler gauge I have goes that small. Could the piston-to-bore clearance exceed those standards and pass a leak down test?  Aside from the motorcycle shop that has my bike I’ve taken pieces of my engine to a machine shop. They work with big Diesel engines. Their front desk has a valve spring sitting on display that’s larger than one of my shock absorbers on my 4Runner. I’ve used them for replacing stripped threads and had them hone my cylinders once. Only real problem I had with them was that everything came back dirtier than before.

The bellowing black smoke condition was always there, well not always. When I first bought the bike, I rebuilt the carbs. It only ran on 3 cylinders and header #4 would only heat up with increased revs. It would only become too hot to touch at mid power. St the time, the only way I had full range of rpms was to lean or choke out carb #4. The carbs wouldn’t synch without  carb 4 being choked out of air. I think i got it to 70 or 80mph with that configuration. I had to tear the engine down latter because I broke the cam adjuster and broke an easy out on top of it. The crankcase was done. I can’t find any videos of the bike running before the first initial tare down 4 years ago but I remember having the smell of burnt oil but with less the visible smoke. What I can say is that the smoke is worse now than it was initially. If it turns out it runs great after tuning, maybe I could get some kind of exhaust filter to mask most of my bike’s musk? Just a note: I have another set carbs now that can synch. It was like wak-a-mole with the original set.

I’ve used an OEM gasket before, but it was a failed experiment with copper gasket spray. Maybe I torqued it wrong or applied the spray incorrectly, but I do have another OEM gasket. I currently have the standard head gasket on my bike that comes with most complete gasket kits. It’s not MLS. The o-rings for dowels and oil valves are from yamiya750. Which I believe is a trusted seller of quality gaskets..?

Well I have two things to attempt now: magnaflow test for the cylinder rack and assembly with OEM gasket. I really hope the the test helps and I need the OEM gasket to seal. I’m skeptical not because of what you told me but of the bike itself. If my cylinders fail the magnaflow test then I’ll find another set to test and once again another set of pistons and rings.


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[calj737]

Huh.. that’s interesting on the clearance, I don’t think the feeler gauge I have goes that small. Could the piston-to-bore clearance exceed those standards and pass a leak down test? 

Nope. Your compression and leakdown tests exonerate the pistons.

[calj737]

Well I have two things to attempt now: magnaflow test for the cylinder rack and assembly with OEM gasket. I really hope the the test helps and I need the OEM gasket to seal. I’m skeptical not because of what you told me but of the bike itself. If my cylinders fail the magnaflow test then I’ll find another set to test and once again another set of pistons and rings.

You need to sort out the carbs and confirm the ignition/coils. Your earlier results indicate an air/fuel issue, not an oil issue.

[camshaft1991]

Ignition coils are new. Carbs aren’t the problem but syncing them would make things clearer. I’m going to synch them myself. That’s one aspect I feel completely competent in.

I’m going to try and see if I still have a loss of power with the carbs synched and then try with cylinder #4 choked out.


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[calj737]

Ignition coils are new. Carbs aren’t the problem but syncing them would make things clearer. I’m going to synch them myself. That’s one aspect I feel completely competent in.

I’m going to try and see if I still have a loss of power with the carbs synched and then try with cylinder #4 choked out.

I could get plugs 1-3 to just about any color. Plug four only comes in two flavors crispy or wet (gas). I could lean out or enrich the whole engine and plug four would be black. It’s not enough oil to stay on the plug. The plug has never felt oily. I know after tinkering with the bike while it’s running, my clothes will start to smell like burnt oil. But if the plug is not oily and the engine burns oil...
I feel I like I need to do more spark plug test again to believe it myself.

Sorry, but your prior post belies your latest. “Ignition” deals with more than just the coils. Points, condensers, leads, caps, AND the reliability of the power to these items. There are a multitude of bikes in this forum that have chased unicorns only to come to find out their “ignition” system was always at fault.

Scottly also just posted:

If anyone has any breakthrough discovers on why CB350F engines bellow out black smoke even after several rebuilds, please let me know.

Black smoke is caused by too much gas for the about of air, producing carbon. Burning oil has more of a bluish tint.

You should heed that insight. Or discard it and hack about. Your time and money.

[camshaft1991]

Sorry I forgot to mention that I have new Diiachi ignition points and condensers. The new coils and spark plug leads were from 4into1 but I bought them through a former freelance mechanic. I can’t remember what brand. I might have a paper receipt on file at my dad’s but the former mechanic had issues with organization. I also replaced the springs to my spark advancer from yamiya750.  The battery is new within a few years and holds a charge well. It still had 9 of 12 volts after 3 months of no use. Lithium battery is on my wish list. The wiring  harness was mended where there were shorts. Rectifier and regulator are original but within tolerance.

I lent the shop my OEM Honda workshop manual. I have a Clymer manual too. They both have similar and different values but I go with the OEM Honda manual if they do differ. The Clymer manual explains better but the Honda manual is law or the next best thing. When I selected my crankcase and con rod bearings the two books conflicted over the color markings. I took a shot in the dark and went with what the OEM Honda manual. No one at time could say one was right over the other. The OEM manual was dated at 1979 while the Clymer manual had half a dozen different editions.  I don’t have them in front of me but I want to say they have no variation when it comes to electrical.

I’m not savvy when it comes to electrical but i had that outsourced by the shop I use. I have an inductive timing light and I have fiddled with advancing and retarding the ignition and adjusting the point gaps. I let them set the timing. I just use my timing light now to check their work. When I get around to getting my bike back and my Honda workshop manual, I’ll go over the timing and test the electrical ignition system.

It’s not black smoke but a thick grey smoke. It’s been almost half a year since I seen it. The smoke usually begins to show as the engine warms up and thickens with increased revs. I remember running the bike either with relatively more clear exhaust and a loss of power or for more power output and a better fogger, but I can’t remember which rebuild I noticed this. I think.. leaning it out produced more smoke and enriching would bog the motor down limit the rpms... the middle ground was a combination of the two I need to post a video.
 
By no means am I going to dive into this with the intention to tear down my engine.  It doesn’t hurt to have post tear down options should everything else fail to determine the cause, but I really do hope my problem is related to the ignition or the carbs and not the engine itself.



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[calj737]

There’s your issue: Daichi points and condensers. Trash bin them. Use TEK brand. Thick grey smoke is a clear sign of A/F issues.

[2wheels]

This may sound stupid but is there any chance you have a chunk ( a large piece ) of rubber in number 4 exhaust.  That starts smoking when it gets hot.

Edit. Is #4 exhaust plugged?

[scottly]

The bellowing black smoke condition was always there, well not always. When I first bought the bike, I rebuilt the carbs. It only ran on 3 cylinders and header #4 would only heat up with increased revs. It would only become too hot to touch at mid power. St the time, the only way I had full range of rpms was to lean or choke out carb #4. The carbs wouldn’t synch without  carb 4 being choked out of air.

It would seem you have a problem with the #4 carb.

[scottly]

maybe I could get some kind of exhaust filter to mask most of my bike’s musk?

[camshaft1991]

DIY catalytic converter lol

Working on the bike now.  My memory has  served me poorly. It’s not just exhaust 4 it’s all of them. I did have an ignition timing problem though. Either I or the mechanic working on it dropped spark plug #1  on its head, to be honest I could have done it. It had no gap. I broke the insulation on the inside when attempting to increase gap but I had more in boxes. It idles relatively well. I cleaned the plugs with acetone, blue shop towels and a brass wire brush. Just so I can get a little white showing again. They are in order left to right 4,3,2,1 in both pictures. I broke spark plug 1 so it’s the new one furthest right. Most of them have gas on them with exception of #1 on the right but #4 to left has more deposit. I soaked the tips again, but I’m going to dry off and let the acetone off gas on the plugs. I’ll upload videos later I don’t have good WiFi right now.



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[flybox1]

1,2,3 look oily 

[camshaft1991]

Yeah I was looking more at the insulator color but I completely disregarded looking at the ground electrodes. If you consider both they all leak oil and more in ascending order. So #1 is the least oily and #4 is the worst.  I only had one go around of cleaning the spark plugs and tuning before calling it a night. No oil has leaked from the cylinder head gasket or anywhere else really so one win.

This is oil leakage from the exhaust. There are holes in the bottom of them for drainage.
The leakage is noticeably more on the right. Might be more oil on the right because of cylinder #1 not firing properly initially, but I’ll have to check again to see how oil accumulates under the exhaust

The bike can idle fine once at operational temperature, but it does have loss of power. My phone won’t let me update videos. When I swapped out spark plug #1, the bike could idle at 1200 rpms. It idled between 1000 and 1400rpms before the swap. The highest achievable rpms is around 7000. However, on return to idle, it stops at 3000 for a minute or two. I have to reverse throttle it a few times to choke it out.

If I rev the bike slightly and continuously to around 3500, all of the vacuum gauges with exception of #2 will increase in vacuum as the engine returns to idle. The gauge could be broken or there is a leak somewhere around carb 2. I need to swap gauges to rule that out then  spray some kind of flammable fluid around the carbs to see if it seeps in. I have valve cleaner spray, i know that’s flammable, but it’s caustic on finished surfaces and is probably not good for rubbers and plastics. I’ll buy starter spray if there are no other alternatives.

Does oil leakage into exhaust affect engine power? I just realized right now that my dad has a snake cam for looking into pipes and I can check my pistons and cylinders for signs of excess/burnt oil without disassembly.



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[scottly]

1,2,3 look oily 

Hard to tell, but it may be gas wetting the plugs?
Cam, do a "clear tube test" to check the fuel levels in the float bowls. Also, to clean fouled spark plugs, burn the black off with a propane torch.

[flybox1]

I would guess the 'stains' on the ground are more from condensation and other crap burning out from inside your pipes.  Unless, your exhaust is full of blue smoke, i highly doubt its just oil.
Have you run it long enough for the pipes to get hot and dry out?  This will stop the drips.

Yes....a borescope is really handy.  I took one on my last bike purchase.  It really helped.
Pull a plug and snake it down the hole.  post pics for us to see.