Topic: CB350F: two failed top end rebuilds, stock bore and 393cc

[markreimer]

Rings have been ordered and on the way 


Looks like the rings broke when this piston hit them. There is a very tiny nick at the edge of the skirt on the bottom. No burrs on it. I'm thinking this is fine to use, what do you think?




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[disco]

Smooth it off with fine sandpaper.... then run it. No problem.

[markreimer]

Finally a bit of progress! noboru gasket kit arrived after being held in customs for 9 days. All I need is that replacement set of rings and I can button this back up. The gasket kit is prettt old but all the rubber feels supple and good quality. Funny looking exhaust gaskets though!




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[markreimer]

started measuring ring gap. Straight out of the package, these ring gaps are measuring .006" / .152mm. I checked near the top and near the bottom of the bore. The stock ring gap range is listed as .1-.3mm, so this is just below the halfway point of the recommended range. The oil ring is a touch tighter at .005" / .127mm

Earlier someone suggested aiming for a mid-range figure for the gap given this engine is bored out to 393 now. Think this is close enough? I'm leaning to installing them as-is, assuming every ring checks out the same.

[markreimer]

Update - I see CB400F stock ring gap is .0059". Mine are reading .006" on most of them. Some are showing .005". I think I'll file fit the tighter ones to hit that same spec

[markreimer]

Cylinder is on! Had a couple of brain farts on the way, but it's together now.

I checked the ring gaps and installed the rings, verifying that they all had the 'top' markings facing up, and the order was correct. I had my first very close OOPS when I realized just before sliding the cylinder down that #2 piston had the two upper rings swapped! Glad that didn't happen. So I fixed that up, installed the pistons in the cylinder, then lowered the cylinders (with pistons inside) onto the rods, sliding the middle two wrist pins and circlips in first, then the outer two. This is my first time assembling a motor this way, and it was actually very easy to do by myself. The big bore totally eliminate the chamfer at the bottom of the cylinder, so it'd be super easy to break a ring without a compressor. This made it easy to ensure the rings made it in safely.

Also, not too proud to admit the second major oops I had. I had the cylinder installed and was cleaning up when I realized I had all four pistons in 180 degrees backwards, with the intake side facing the exhaust!!    Thankfully it only took about 30-40 minutes to pull it apart, switch them around and get it all back together. I really like this method of top end rebuilding. Aligning the rod with the wrist pin is a little tricky, but not too bad.

Next up is cleaning up the gasket surface on the head, applying some Hondabond around the main oil supply and return seals, copper coat on the head gasket, and torque the head down. I've got new rubber dampers for the cam chain tensioner, some new camshaft sprocket bolts, and a few other goodies to install, plus a quick carb inspection before buttoning it all up and givin 'er some gas. I'm gone this weekend but hope to fire it up next week at my weekly moto shop night with the guys.

[calj737]

Mark - one tool I use an awful lot in my shop is a stainless steel brush, a large one and a small one (like a toothbrush). These are excellent for cleaning aluminum, or in this case, the mating surfaces as they won't scratch the steel. You can get them at Harbor Freight, Northern Tool, or any local welding supply store. They're much softer than brass and steel and actually will break up the oxidation on aluminum for cleaning.

[markreimer]

Cool I'll look into that! I've always just used a razor blade to start, then scotchbrite. That sounds good.

[MetroRedneck]

Second on the stainless brushes.  I find I save time over blades and scotch bright too.

[markreimer]

So something like this, but smaller?

http://www.canadiantire.ca/en/pdp/stainless-steel-wire-brush-0588105p.html

Or these:

https://www.amazon.ca/dp/B01M34Q848

And that doesn't damage the aluminum gasket surface?

[calj737]

Exactly like those, and nope, no damage whatsoever to aluminum or the mating surfaces.

[markreimer]

Thank you Cal for the stainless steel brush tip! It was awesome for cleaning up the head gasket surface!

I made big progress today. The engine is basically done but sitting for a few days before I retorque the studs.

I double checked all the oil passages were clean, then applied a thin smear of hondabond around the supply and return lines on both sides of the base gasket.

The head gasket got a few coats of coppercoat in thin stages. I applied hondabond to the outside face of the oil supply seals, very thin and being sure to stay far away from the little holes in the restrictor.

With the head gasket tacky, I installed the cam chain tensioner with new rubber dampers, then the head, and then torqued it down. Next was the cam, and man did I have a time getting the sprocket and chain on. I think the chain wasn't sitting on the lower sprocket properly. A few rotations of the crank and everything fell into place. Assembly lube was applied to the cam bearing journals. Torqued some new cam sprocket bolts down, and my work is done for the day!

Well kinda, couldn't resist opening the carbs and cleaning them up, as well as installing new exhaust gaskets and bolting the pipe on. Now all I have left is cylinder torque, install carbs, valve clearance, add fresh oil and see how it runs.

That'll all happen Thursday.




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[ekpent]

  Lookin' good,bet your anxious to get it all wrapped up and press that starter button for the big moment.

[markreimer]

It's killing me! This bike has sat since the spring, I just didn't have the time and money to deal with it. I'm really hoping this engine rebuild makes it as reliable as my 750. I don't see why it wouldn't.. I know the bottom end is solid, and now it has fresh pistons, rings, valve seats cut and so on. If it runs well for the rest of the season I'll start focusing on the many cosmetic improvements it could use 

[markreimer]

Oh and I forgot to note one thing for the build thread

I looked into the intake and exhaust ports to see if there was any indication of oil weeping down the guides, thinking that might have contributed to the heavy carbon fouling of the piston tops and valves, and the burning oil. I did have a valve job done right before this happened though, with seats cut and guide clearance checked. When I pulled the valves, one of them had a tiny nick from the keeper, and I was worried it might have scratched a guide on the way out.

I found evidence of some oil in the #4 exhaust port, which was the cylinder that was burning massive amounts of oil relative to the others. I removed the keeper and springs, and pulled the valve out to inspect the guide. The guide appeared to be perfect with no signs of scratching or damage. So I'm guessing that the bit of oil I saw in the port was blown out during combustion. The oil likely entered the cylinder by sneaking past the rings, and any unburned oil remaining was blown out the exhaust, leaving some wet spots in the port.


Does that rationale make sense? Again, the guide looked good and the clearance measured within spec. The exhaust guides do not have seals on this year.

[MRieck]

Cylinder is on! Had a couple of brain farts on the way, but it's together now.

I checked the ring gaps and installed the rings, verifying that they all had the 'top' markings facing up, and the order was correct. I had my first very close OOPS when I realized just before sliding the cylinder down that #2 piston had the two upper rings swapped! Glad that didn't happen. So I fixed that up, installed the pistons in the cylinder, then lowered the cylinders (with pistons inside) onto the rods, sliding the middle two wrist pins and circlips in first, then the outer two. This is my first time assembling a motor this way, and it was actually very easy to do by myself. The big bore totally eliminate the chamfer at the bottom of the cylinder, so it'd be super easy to break a ring without a compressor. This made it easy to ensure the rings made it in safely.

The machine shop should have cut a new chamfer. I'm only mentioning it as it may help somebody in the future. If you don't know the shop always ask.

[markreimer]

Well technically there was a chamfer, but it was tiiiiiiiiny. Boring it out to 393 has made the barrels super thin at the bottom. If the taper was any wider the cylinders would be knife edged on the bottom. Sure would have helped, although I gotta say installing the pistons in first made the whole process really easy.

[markreimer]

Motor is done!

More big progress today. I retorqued the cylinder studs, double checked the cam timing, lubed everything with engine oil and bolted the valve cover down.

Installed the carbs after much coarse language, and hooked up the control cables. I've always hated the throttle cable routing on this bike as one cable protrudes directly into the frame spine, producing a sharp bend that makes for a stiff throttle. Gonna have to work that issue out soon.

Anyway, I assembled the rest of the bike, put fresh oil in and went to start it up, only to realize I had no spark plugs and no gas!! Doh!! Gonna have to wait another day or two. But I did hit the starter a few times with no plugs in, and it spun up nicely, building oil pressure and shutting the oil light off.

Next chance I get I'll put plugs in, fresh gas, check the points gap and giver.


Forgot my phone though, no pics today


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[markreimer]

Just got back from my first ride on the cb393f!

A few concerns and comments.

First the good; fired up immediately and the engine sounds great. Much smoother and quieter than before. Settled into a pleasant idle.

The concern:
It was very smokey right off the bat. However, I did burn several liters of oil through that pipe, so I'm sure there is some stuff burning off in there.

I went for a quick test ride and it felt great. Pulled well and sounded good. But smokey. Yes, all the rings are in correctly, I double checked and had someone else confirm!

I got back and pulled the #4 plug, which is the cylinder that was mega fouled in spring. It looked perfect! Nice and tan. I parked it for an hour or two

Went for a second test ride, a bit longer this time. Again it fired up well and felt great. When I got back I decided to pull all four plugs to see. #1 was wet. I don't THINK it was wet with oil, but with gas. #2 also looked gassy, 3/4 were dark but dry. I did the sniff test, but it was inconclusive. I didn't really smell anything

What do you think based on the photos? I wiped the wet #1 plug wth my finger and didn't get any black marks on my skin. But the oil is brand new, so it wouldn't really be black yet I'd suspect?

So I'm thinking I have a fuel or maybe ignition issue. I have cruisin image jets in there now, I believe 35. But these plugs look very rich. Stock needle I believe.

I DO know that my petcock has a very slow leak. And the two wet plugs are the lower side of the engine when it's on the sidestand, which is how I had it parked. So maybe I have a carb issue that caused the plugs to get wet while parked for two hours. But wouldn't that have burned off after a 5 minute ride?

Is there a way to confirm this is fuel and not oil? I held a match to the wet plug and it didn't catch fire...



1-4 after I wiped the plug with my finger.






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[seanbarney41]

If your baffle got oil soaked, it does take a surprisingly long time to burn it out.

[markreimer]

Yeah I'm thinking so, and not getting too worried just yet.

I think I'll start by pulling the carbs and replacing the slow jets. I found a set of Keihin 35's, still in the package. I forgot I had them! So I can at least verify that I've got the right slow jets, and check the float levels while I'm in there. I'll order Keihin mains as well today so the carb is all OEM.

I know my petcock has a slow leak as well, pretty sure it's leaking past the two fibre washers under the screws that bolt it to the tank. I'll fix that up as well, as I'm thinking it's possible that the wetness might have been from fuel leaking into the chamber while it was parked, wetting the plug, before I pulled them. May as well try these easy things first.

Once those two are done, I'll take it for ride for a few hours and see if I can't burn out that oily pipe. it doesn't smell like burning oil, not like it did before. And it's not a huge plume of blue smoke so far as I can tell. It was night time, so I'll have to check again in the daylight. It smelled gassy to me, not oily.

Another possible cause of gas fouled plugs could be ignition. I have the original set of points on there. I've only heard bad things about the Diacchi replacements, but OEM is hard to find and very $$$. I could almost just put a Pamco in there for the same price. Anyone have a line on reasonably priced OEM points and condensors? I'll trip back the spark plug wires and replace the caps too, they are originals.

[flybox1]

If you replaced the float valves with aftermarket, your float level will need to be near 24mm (not 21mm as mentioned in the shop manual and clymer)
If so, this (high fuel level) may account for rich plugs.  Clear tube test will really show where you need to go.

[markreimer]

Thanks, I did infact replace the float valves. The originals were damaged during disassembly, it had been sitting outside for... 41 years lol. I'll check with the clear tube method!

[Ridem32]

I would take it out and ride it some. Let the motor get some miles on it and get broke in.  You said it runs good. Ride ride ride it. Then if plugs still look like rich fuel check out the carbs. I think your a little gun shy from before


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[markreimer]

Bad news.

Just got in from a 70 mile ride, all highway. The bike smoked like a chimney the entire time. Someone asked if I was on fire haha. It's burning huge amount of oil. Oil was spitting out at the header/pipe connection.

It smokes at all times. At idle, then a thick stream while accelerating, and even more after rolling on the throttle after engine braking.

After 60 miles I checked the oil. The dipstick was dry!! I had to add 1.5L to get t back to full.
 
What's strange is the engine absolutely hauls compared to last year. It pulls steady and hard all the way to 100mph in 5th without tucking. It never did that before. It feels strong and smooth but just so smokey.

I'm not sure where to start here. I know the rings are in right side up. I know the piston to bore gap was done within spec. The valve clearances were in spec and the faces cut. What could it be? What could cause such massive oil consumption?

Please help, I'm so bummed






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