SOHC.co.uk Forums > CB350/400

New cam chain tensioner or not?

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AshimotoK0:

--- Quote from: Bryanj on August 04, 2014, 07:42:57 AM ---As long as the horshoe pivots freely and the plunger is free in the casing I would only replace the springs on the plunger as they were only just strong enough when new.

Check the blade for cracking where it bends at the ends and the cushion for rubber loss replace either if faults fond---The tensioner blade can be replaced with just a cam cover off but the cushion needs the head off and barells lifted

--- End quote ---
Agreed Bryan. I have all NOS rubber parts for my 750K0 when I get round to assembling it  but also some really nice used rubber parts, some of which have been off the bike for almost 30 years and kept away from sunlight (i.e no ozone cracking). I guess we will all open up engines which have possibly been apart in fairly  recent times and the parts fitted may not be that old. Sometime,  I am going to take my NOS parts out and measure the rubber hardness on the NOS part and compare with some old, but real nice condition, parts just to see what the difference in hardness is.

Cheers ... AshD

Clem2112:
I used what I thought was the strongest pair of springs from two engines - there seems to be no specified measurement for free length or condition.

They seem to lose their strength but by how much?

I also checked the plunger for straightness and any sign of wear or ovality on the flat part as that's where they can jam up in the casing hole.
Needless to say, manual tensioning is still needed on mine !

When removing the tensioner blade with the head removed, that cushioned seating piece can sometimes lift out of its pocket in the arm.  Worth a look with a torch to check it's still there when you put a new blade in.

Drew400:
Thank you all, sound advice as always from people who've been there. You may have just saved me a few bob, not least as this little 400 will be looking forward to a long, dry, easy retirement... if and when I get her running again. This'll not be a daily winter commuter in my ownership!

Cheers for now,

D.

Trigger:
I agree with bryan. I have built 21 CB400 engines in the last 2 years and everyone has been different. Had one with under 30,000 miles (well that what the customer told me). The oil was like glue, the oil pump was shot and all the tolerances were well past its spec. Had a 98,000 one in that the guy had from new and it had been well looked after with regular oil changes. He had the cam chain changed every 15,000 mile (if he needed it or not).  It was a privilege to work on such a fine example. Only needed rings, chains, cam blades, seals and a gasket set.
I have seen primary chains worn out in 4,000 miles and have seen other last 70,000 before it starts to rattle under 1500 rpm. It is all down to who had the bike before and if they looked after it.

Drew400:
Thanks Trigger,

Somewhere in the last 10 or so owners it was either abused or neglected then repaired. This is certainly not a well cared for, one owner bike. Hopefully it will feel like one when I get it all back together, albeit with some genuine 'patina' visible.

Hmmm 21 x 400's, eh? This is my first 400 and my first ever engine that involved bottom end stuff. Learning loads and spending too much time in my garage. Great fun in the man shed!

Cheers, D.

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