CB400F Engine Rebuild

Joined
Mar 11, 2007
Messages
1,494
Location
Texas
Bike
2013 Triumph Trophy
While I'm looking for some NOS parts to start back on the SL100, I decided to rebuild the engine in the CB400F. The cam chain tensioner was toast and you have to split the cases to repair it.

I've decided to tear it down in the frame because it's too heavy for me to lift it out by myself.

I have cases ready for the rebuild.



The opening for the countershaft has scratches in it. They don't go all the way across but I'm thinking I could fill them in. Do you think that is necessary or can I ignore them?



Lots of signs of poor maintenance on the bike. It has the wrong clutch cable--it doesn't even screw into the engine case.



But it does look like someone put a new rotor and stator in fairly recently.





The carbs worked fine, but they really could use some cosmetic work. I'll fix the corrosion issues and replace the o-rings inside.









Once I got the cylinder head off, I could see the cam chain was very loose, I could hear it rubbing on something inside when I turned the crank to pull the cam chain sprocket. I could also pull it off the sprocket with my finger. The tensioner definitely isn't working. Both the cam tensioner and guide are very worn.









I got 7 out of 8 exhaust studs easily and the last one broke. Figures.

The cylinder is stuck, it's gotta be at the base gasket because it turns over very easily. I quit today before I broke something from impatience.



I smacked the bottom of the cylinder with a cold chisel ground down to approximate the shape of the cylinder. It just took a light tap and the cylinder was free. However, this was as far as it would go. The pistons were free, but it felt like the middle studs were holding it up. After half an hour of reefing on it, I got a wooden drift and smacked it on the bottom a few times.



After a few taps, this fell out of the cylinder.





It's some kind of plastic putty that was put into the slot in the front of the cylinder where the studs pass through the fins. You can even see the the person's finger prints who put it there. Nothing about it in the manual. A few taps with a small screwdriver and it was out and the cylinder was free.

This was where it was, four of them.



Now I can lift it out of the bike and put it on the bench.



I measured the bores and all are in tolerance so I'll just have it honed. The rings look good and it wasn't burning oil so I'll reuse them. The max outside measurement is 2.012.

Cylinder measurement at the top Measurement at the bottom
1 2.006X2.006 1.994X2.004
2 2.007X2.006 1.994X2.009
3 2.008X2.007 1.986X2.005
4 2.005X2.009 1.996X2.007

All four pistons were above the 2.002 minimum.

I'll split the cases and move the transmission to the new cases and then check the crank and main bearings with plastigauge. The head will go to the machine shop for a full inspection and minimum of new valve seals.
 

SupraSabre

48 Years of SoCal Lane Splitting/Commuting-Retired
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Nov 20, 2005
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Cedar City, Utah
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12/04 ST 1300s
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000145
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Looks like a good project. I remember the 400's, always looked like fun bikes to ride!
 

Stump

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Las Vegas, Nv
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VFR1200X
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Really fun motor. I built up one using Yoshima pistons, Corrello rods, bored out carbs, etc back in the early 80's. Was a sweet little motor that redlined at 14000 rpm. I raced it some in SoCal before selling it. I always loved the sound of the motor screaming down the straights.

I certainly don't remember any plastic plugs on the cylinders! I do remember getting frustrated with the valve seals leaking tho!
 
Joined
Aug 15, 2011
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461
Location
Covington, GA
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2008 ST1300
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8494
When I was growing up a Doctor down the road had a 72 Benz Convertable 2 door (dont know the model) and a 70-72 CB350 4 cylinder bike....Both in Silver. The Doc asked me on several occasions to take the bike around the nieghborhood after I finished cutting his grass as "he was in his 80's and didnt get around like he used too."


I tried and tried and tried but could not get him too sell me that bike.


It was a genuine pleasure to cruise on.



Looks like you have a good handle on this restoration!
 
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bmcdonau
Joined
Mar 11, 2007
Messages
1,494
Location
Texas
Bike
2013 Triumph Trophy
Today I finished stripping the cases so I could take them apart to look at the cam tensioner. Here's some pics of the disassembly

Every bike I work on seems to need a different size flywheel puller.



I discovered that it's easier to break these philip's screws with vice grips, even with very little room like there is here.



This bike has one of the most complex gearshift linkage I have ever seen.









Here's the problem.

The cam chain was really loose because someone had broken off the adjuster bolt and couldn't properly tension it. Soon it was loose enough to rub on the horseshoe and then it jammed up and wouldn't move.



I can't even get the springs and adjuster rod out of the case.



It's hard to tell from the pictures, but 1 and 4 need replaced as they are scored. Just for grins I moved all the shells from the old cases to the new cases and measured the clearance with plastigauge. All except one set were in tolerance.

Then I measured the clearance on all five bearings with plastigauge by moving the one new set of bearings (green) from location to location. Again, they were all in tolerance even though number 4 was iffy with a C. I'm going to end up with CCCDC in the new cases. Originally the motor came with CCCCB in the old cases.

All the crank journals are larger than the largest listed in the Clymer manual so there has been little to no wear on the crank.

This clearance is between 2 and 3.



The clearance here is is between .002 and .003



The clearance here is between .001 and .002.



This was the worst, really iffy 3 so I'm going to go up one thicker bearing.

 
Joined
Feb 5, 2005
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77
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Kingman, Arizona
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2000 ST1100 ABS TCS
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004
Meticulous work. Good on ya.

In '75, my next door neighbor went with when I picked up my new GL1000. He bought a CB400F. Last time I saw it (sometime in 78) it was leaning against the garage wall, outside, right under the (no gutters) eve. Ugly site. Probably only had <2000 miles. Total waste of money on his part and a waste of a nice motorcycle.

Gott a say, the CB-1 (400 cc, 88 and 89 models in the US) was a totally better bike than the older CB400F.
 
Joined
Mar 21, 2010
Messages
383
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N. Ga
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2012 GL1800 III
Good luck with your restore , my first Street bike was a cb350Four , made a lot of party money racing other bikes with it. Only thing quicker in the 500cc down size was the Yammi RD350/400 2 strokes.
 
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bmcdonau
Joined
Mar 11, 2007
Messages
1,494
Location
Texas
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2013 Triumph Trophy
Meticulous work. Good on ya.

In '75, my next door neighbor went with when I picked up my new GL1000. He bought a CB400F. Last time I saw it (sometime in 78) it was leaning against the garage wall, outside, right under the (no gutters) eve. Ugly site. Probably only had <2000 miles. Total waste of money on his part and a waste of a nice motorcycle.

Gott a say, the CB-1 (400 cc, 88 and 89 models in the US) was a totally better bike than the older CB400F.
Katherine would say anal!:D I only want to do this once so I'm trying to do it right. I was worried because some of the bearing shells are no longer available. fortunately, the the thin ones seem to be the ones they are out of. I'm cleaning the cases while waiting for the new parts to arrive.
 
Joined
Aug 1, 2007
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I wouldn't recommend re-using the rings if you're going this far. Especially if you are going to hone the cylinders. Might end up with a smoker.
 
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bmcdonau
Joined
Mar 11, 2007
Messages
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Location
Texas
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2013 Triumph Trophy
I dropped the cylinder and head off at the machine shop today. I should have them back by the end of next week. If everything goes well, they'll replace the valve stem seals and that'll be it. I went through the gasket set and determined which o-rings I need that were not supplied and will order them tomorrow.
 
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bmcdonau
Joined
Mar 11, 2007
Messages
1,494
Location
Texas
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2013 Triumph Trophy
I wouldn't recommend re-using the rings if you're going this far. Especially if you are going to hone the cylinders. Might end up with a smoker.
Yeah, I thought about that. I'm going to find out what the machine shop says about the bore before I decide what to do.
 
Joined
May 29, 2010
Messages
145
Location
Robinson,IL
I always wanted a CB400 or 350, heck I still do. You are also doing a SL100? My first bike was a Candy Apple Green 1971 SL125. ( wish I still had it )
As far as your question regarding the nicks in the countershaft flange, my two cents is that I would repair them. Anything that is a radial scratch over 50% of the sealing surface should probably be repaired. There is a company belzona.com that sells material that would probably fix you right up. I have been around their product for restoring corroded and mechanically damaged steel, and it works wonders, I would think that they also had products for aluminum.
 
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bmcdonau
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Mar 11, 2007
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1,494
Location
Texas
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2013 Triumph Trophy
While waiting for parts I decided to start on the carbs.

I started disassembing the carbs to clean and rebuild them. The rack disassembly went well....then I started taking apart number 4.

What the heck is this brown stuff.....uh ooh.





A bodge as the English would say. How the heck do you break this? My first thought was to buy another set off of e-bay, but as luck would have it, none are currently for sale.

I wondered how I could fix it since I didn't have the other part....then it hit me, first I'll have to make this jagged edge square.



A little work with a dremel.



A quick search of the garage and I found this brass rod.





My first thought is to use JB weld or something to glue it, but I didn't think that would hold it without some type of support. I decided to drill out the brass and carb and Jb weld a drill bit between the two.







and I need a hole across the rod for the float pivot pin.



I still wasn't sold on JB weld so I rifled my brass drawer and found smaller diameter rod! I got excited and didn't take any pics, but this is what I fabricated. The small rod is soldered into the larger one.



I had to use a propane torch because my soldering gun wouldn't heat the brass enough to melt the solder.



Its an interfrerence fit in the carb so no JB weld required!
 
Joined
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004
Hope the line bore between the posts is accurate. :D

Good fix, tho the cotter pin was ingenious. :D
 
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bmcdonau
Joined
Mar 11, 2007
Messages
1,494
Location
Texas
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2013 Triumph Trophy
I cleaned the number three carb and put it back together, but the rusted parts haven't been plated yet so it's only loosely assembled. I haven't decided if I'm going to clean all the hardware or try to replace some of it.





Before and after of some of the hardware.





My manual is at the machine shop while they check my head and cylinder so I looked up the float height on SOHC Fours and it said 21 mm. This doesn't look right.



What exactly does this black thing do? Number 4 broke while I was messing with the broken casting. It looks like it is a spacer.

 
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