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1967 CB450K0 Black Bomber Rebuild - By Royhall
Bryanj:
I had forgotten just how long those studs are!
Laverda Dave:
Impressive progress Roy 👍.
MCTID:
Looking good Roy. The massive Journal Bearing Housings are things of wonder........Honda didn't intend that Crank to 'flex' did they.....reminds me of the Gearboxes on the Overhead Cranes I used to work on many moons ago.........'made in Scotland frae girders' !!!!!
Keep up the good work, excellent commentary and great photees......each one worth a 'thousand words'.
royhall:
This photo gives a better view of the journals. Fairly robust item so not sure why it was changed for later models, maybe another easier to machine cost saving who knows.
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royhall:
Now where were we? The crankcases are together and ready to work on the two sides.
It would appear from comments made on this forum and others that the Bomber suffers from low oil pressure to the cams. The outcome is usually the failure of the exhaust cam which are now virtually unobtainable. My exhaust cam has suffered with slight pitting on one cam lobe. The repair theory was to fit the larger aluminium bodied oil pump from the later 450's or the 500T. Jensen tested this theory and found that due to the larger diameter pump piston it pushed the connecting rod off centre causing wear. So with that in mind, and the fact that having a garage full of bikes it's never going to see high mileage, I have decided to stick with the standard 450 pump. The early pumps also suffered from poor design around the pick-up that caused oil to be drawn in causing a vortex that wore a hole in the pumps debris screen. My existing pump has this problem.
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I had a look around for a NOS standard pump and couldn't find one so put a "part request" on the Silvers site. I only had to wait a week for the DSS email to say he had one in stock, a bit pricey at £210 but needs must.
Before the pump and clutch can go in I reassembled the gearchange mechanism and springs (very fiddly) and checked they functioned freely. This mechanism is very simple and well thought out, top marks there Honda.
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The pump is a reciprocating type that drives off a large oil fed offset boss on the back of the clutch basket. The pump and the clutch needs to be fitted together as one unit (this is a real bind if you need to access the pump as the entire clutch has to be removed to get at it). Before that started I checked all the clutch components for damage and wear and found them to be in really good order. The clutch plain plates were checked for wear and warping and were also good. New friction plates came from Wemoto and are Vesrah.
I gave the pump boss a good coat of Graphegen and oil before assembly as it may take a while for oil flow to reach that area and I don't want the new pump connecting rod to end up scored. The pump and clutch were assembled and torqued down using all new locking tabs for security. I have also fitted a new clutch push rod as the existing item was badly corroded around the seal area and may have ended up being the cause of a leak. After assembly I dropped the cam chain down off it's crank sprocket and checked that the engine was free to rotate smoothly. All was very good so am well pleased.
(There's my lovely daily rider CB750F2 in the background. She's a babe)
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I found on the strip down that my "low mileage" engine was on its last rebore size that was also worn out. I managed to source another barrel from DK that was on standard size but had rust in one barrel. The eBay price was £60 so I offered £35 and stuck to my guns and got it for £38 so not a bad deal, or so I thought. After very good reviews and a few recommends on this site I decided to go with the Cruzinimage piston kit at plus 0.5mm. This skips an oversize but due to the light rust in one barrel it would give enough meat to clean it up. My engineer rebored the bad barrel first and it didn't clean up so he took it out to plus 1mm and it still didn't clean up. We pressed the liner out and weirdly the rust had gone right through to the outside of the liner. Emailed DK who didn't have another barrel on stock size so refunded my £38 no problem (what a superb outfit they are). So I'm without a barrel. Then like a Knight in shining armour along comes Ash's amazing stash and offers up a barrel for free, many thanks for that Ash. As I now had the piston kit I may as well use it so it bored out lovely to plus 0.5mm.
With the barrel rebored to 1 thou clearance and the piston kit fitted and new gaskets, the barrels went straight on.
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Another weak point on the Bomber (and hence the parts are rarer than rare) is the starter clutch. It appears the clutch back plate is a bit thin and tends to push the rollers out that bends the plate and then it jams. And you don't really want your starter being dragged around at crank speed as it doesn't do it any good and makes a bit of noise. So I gave mine a good looking at and all parts looked straight and wear free so it was assembled onto the crank and tested. Worked spot on. Thought I would pop the new engine sprocket on whilst I was at it, with a new lock ring and bolts for security.
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Looking good so far and no problems that I haven't been able to overcome. I took the precaution of putting lengths of coat hanger wire through the cam chain ends, it would be a shame to have it fall into the engine as it looks like it would be very difficult to fish it out again.
More next time.
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