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Discussion Starter · #1 ·
Hello Twin friends,
Thanks to Longdistancerider for some early info on these two engine differances and his input to this site's knowlege bank. Hopfully this thread will answer this age long question as I don't think anyone has completed this conversion yet.
I'm converting my CB400t to a 450 using all existing 400 parts except cylinder barrels, pistons/rings and connecting rods. Note: You do need 450 wrist pins as they are larger @ 18mm
1st thing to address is that the upper case won't accept the larger 450 barrels. I took mine to 2 engine machining shops and they couldn't easily bore them out because they are not round to start with!
One advised to just use a die grinder and bore it myself.
I have a die grinder, so I bought a large 30mm x 12mm carbide burr and got to work on the upper case
 

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Discussion Starter · #3 · (Edited)
Test fitting

Nearly done. Auto part


One main point here is that this IS NOT a precise fitting of the barrels to the upper case. The factory fit wasn't tight or precise, the exact placement is from the dowels. You need to make sure there is enough contact for the gasket to seal the oil in.
 

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This will be enlightening. Did you use a 450 base gasket and scribe the case for the diameter of the cylinder bores? I'd keep checking the fit of the 450 to 400 as you grind to try from grinding out too much. Look carefully at the top rear head bolt holes in the 400 cylinder, that needs to be as exact as possible on the 450 so you get proper oil flow and it also seals.
 

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Discussion Starter · #5 · (Edited)
Gasket

The only problem with this is that the 450 gasket does not have the oil path of the 400 so I just cut it out, using the 400 gasket as a template. I kept checking against the upper case after each cut.
I cut the 450 gasket with a sharp box cutter. Expect these contain asbestos (or **** that is just a bad) and don't use power tools on them.
The oil path for cam/rocker etc. lubrication is different on the two engines. The 450 has a cooler and the supply to the cam etc. is via a external pipe.
It seems the 400 is a high pressure/low volume supply that flows up the two rear bolt cavities. This works fine, so I'm sticking with it. It also supplies each end of the cam first. (The 450 seems to be in the middle)
 

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Discussion Starter · #7 ·
Fit

Hi LDR,
yes I used the 450 gasket and only did what I needed to. One hard part is that the 450 cylinder sleeves are 5mm longer or so. (For no reason that I can see) So I had to cut out some of the shoulder (30mm down from mating surface) Tire Automotive tire Auto part Gas
 

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Discussion Starter · #9 · (Edited)
There's no asbestos in these gaskets, that was only found in head and exhaust gaskets in the 1960's and earlier.
That's good news-I would hope so. None of the stuff used in these is good to turn to dust though. I know I did it for years (used power tools on everything) until I read all the things that can have carcinogens in them. Even modern clutches and brakes test positive, though they are not supposed to use it now.
My idea is to give the education to the guy's in their 20 that have no idea about the potential health hazards through old cars and bikes etc because I wish I was more careful.
 

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Discussion Starter · #10 ·
One main thing I will point out is that I'm Australia and we had no CB or CM 450's imported here. I'am doing this at the risk of it not working and paying for new parts not available here.
I have had to buy all the conversion parts from the US (ebay)
If I was in the US I would just rebuild a std 450 to put in. The postage of a whole engine to Australia would not be worth the cost.
I'm happy with 5 gears and get to keep the kick starter(never use it though :) I also get to keep the original engine number and the bike is seemingly unmodified - We have laws here in Australia.
 

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Discussion Starter · #11 · (Edited)
I now need to order a heap of normal rebuild parts. Things I need advice on: Oil pump chain- They seem to always be loose, but do they ever break?

Cam chain will be replaced, along with the tensioner. Guide on the other side looks ok- anything here I'm missing?

I think I will replace the balancer chain as it was at the end of it's adjustment. Also it's guides were obviously worn with deep grooves so I'm guessing it's important to replace those too? Auto part Automotive engine part Machine Engine
 

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Discussion Starter · #13 · (Edited)
Update:I have been ordering lots of NOS parts: Cam chain/tensioner, Crank bearings, Conrod bearings, Transmission bearings, Balancer chain and guides, Clutch springs and clutch bearing, Piston rings etc. I have also welded the balancers solid because the rubbers were starting to break apart. (450 balancers are solid). I also ported the head and dropped it off for the seats to be re cut.
 

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400 balancers deteriorating is common, I've heard of folks replacing them with the 450 balancers, first I've heard of welding them. It seems it would require some pretty advanced skills and equipment to get them perfect. Perhaps you could expand on your process a bit more?
 

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Discussion Starter · #17 · (Edited)
400 balancers deteriorating is common, I've heard of folks replacing them with the 450 balancers, first I've heard of welding them. It seems it would require some pretty advanced skills and equipment to get them perfect. Perhaps you could expand on your process a bit more?
Not that hard, replace rubbers with some small offcuts of steel and weld in to make sure they don't move too much. I weighed them before and after to make sure they are the same. I did take a few pics before rebuilding them. Bicycle part Auto part Bicycle drivetrain part Crankset Rim
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