Author Topic: CB400F engine in a CB530F, heard rumors; seeking facts  (Read 3125 times)

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thirdman

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CB400F engine in a CB530F, heard rumors; seeking facts
« on: April 19, 2005, 03:03:20 PM »
I have heard rumors that the CB400F engine can be dropped directly into a CB350F frame.  Can anyone back this up?  Has anyone actually DONE it?

Also, I have heard rumors that one can simply bolt-on jugs and pistons from the 400 onto the 350, making it a poor-man's rebore.  Again, truth or simply rumor?  Has anyone actually DONE it?

Thanks!


don_m

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Re: CB400F engine in a CB530F, heard rumors; seeking facts
« Reply #1 on: April 19, 2005, 07:59:44 PM »
Having owned my 1972 CB350F from new, (199,000 miles) I'm somewhat familier with this model.  The bottom end, crankshaft, rods, etc. is the same as the 400F.  The 400F cylinders are larger & will not drop in a 350F crankcase without machining the cases.  The 400F head is also different & will not fit a 350F cylinder block.  Other top end parts, cam, rockerbox cam chain & tensioner are the same.  You can bore the 350F cylinders to fit 400F pistons.  They will be thin but mine have over 150,00 miles on +0.040 400F pistons & are still going strong & are a close fit.  I chamfered the combuston chambers for clearance, which also provided a "squish band" to improve combustion.  Other mods were necessary to intake & exhaust flow to optimize performance.

Offline SteveD CB500F

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Re: CB400F engine in a CB530F, heard rumors; seeking facts
« Reply #2 on: April 20, 2005, 01:50:20 AM »
200k miles from new!!

You have my admiration Don (I thought 50k on my 500 was a feat!)

Let's see some pictures - post on "What Bike" Poll.

Cheers and Welcome.  Steve.
SOHC4 Member #2393
2015 Tiger 800 XRT
1971 CB500K0 (US Model)

thirdman

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Re: CB400F engine in a CB530F, heard rumors; seeking facts
« Reply #3 on: April 20, 2005, 09:19:23 AM »
Having owned my 1972 CB350F from new, (199,000 miles) I'm somewhat familier with this model.

Thanks, Don... that's good stuff.  Only "somewhat" familiar after 200k miles?   :D

don_m

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Re: CB400F engine in a CB530F, heard rumors; seeking facts
« Reply #4 on: April 20, 2005, 01:58:48 PM »
"Somewhat" as I gain experience by working on my machines.  The little four has needed little over the 3+ decades I've ridden it.  First problem, & the only one ever with the bottom end was an engine lockup at about 30,000 miles.  Being an experience mechanic I took it apart, (with the help of the Clymer's manual), & found the primary chain had failed.  It was stamped: "Hyvo, made in USA"!  The replacement was Japanese and has been in since.  By then I was not happy with the anemic performance so tried a few things.  Overboring 5mm to 52 total gave 425cc.  The cylinder liners are thin, but not thinner than my BSA B50MX with 550cc kit.  The mod greatly increased the low end torque but predictably did not help top end performance.  I also had oil leaks from the top end oil gallery so pulled the head.  The ports were rough & poorly blended compared to my Brit bikes so some careful work with cutters & files cleaned up the contours.  The persistant leaks were caused by the rubber cylindrical seals not being confined within the head gasket, allowing them to mushroom out & loosing the sealing pressure.  I took a compression sleeve from a brass tubing fitting that was the right size, & cut it in half, across the diameter.  After filing & sanding the two pieces, now having triangular cross section, to 0.060 thickness, I placed them over the rubber sleevse.  The 0.060 made them slightly higher than the 0.050 head gasket.  Now they seal for years without problem.  The difference in performance is remarkable & I have shocked a lot of riders of other machines!  Not a superbike, but it is a very lively little machine.  The next time I pulled the head was at about 100,000 miles when low compression was noticed on one cylinder.  The rubber seals had self destructed but the metal rings held the oil without leaking.  The compression problem was solved by replacing one exaust valve, also the cam chain guide & tensioner blade.  Recently, at 190,000 miles the engine started using a lot of oil.  Teardown revealed one piston with shattered top ring which damaged the bore & piston as well as pitting both valves.  Dropping in a replacement sleeve & reboring as well as the two valves & one other fixed the problems.  Also replaced the cam chain & guides again.  While I was at it I dismantled the bike, cleaning up & painting as needed.  (Everything needed attention).  I now have 199,000 miles & the bike runs much better than new, (and looks good, too).  There have been a few other, minor repairs but it has never left me stranded.
For comparison, I have a lot more than "somewhat" experience repairing my Matchless G12CSR that I've owned almost as long!

Offline heffay

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Re: CB400F engine in a CB530F, heard rumors; seeking facts
« Reply #5 on: April 20, 2005, 06:26:28 PM »
don m~
if you do the things that you say you do (or at least the things your sohc4 does)... you are an asset to us all
heffay
Today: '73 cb350f, '96 Ducati 900 Supersport
Past Rides: '72 tc125, '94 cbr600f2, '76 rd400, '89 ex500, '93 KTM-125exc, '92 zx7r, '93 Banshee, '83 ATC250R, 77/75 cb400f

don_m

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Re: CB400F engine in a CB530F, heard rumors; seeking facts
« Reply #6 on: April 21, 2005, 02:32:54 PM »
Come down to (sometimes) sunny SoCal & take a ride on it.  Forks & brakes are stock, shocks are Red Wing.  These machines are very nimble & fun to ride.  The brakes arn't much but I don't use them much, either.  Don_m battlecry: "Brakes, man--You don't want brakes--They slow you down!