SOHC.co.uk Forums > CB350/400

Winter Work

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hondatri:
Hi I am back again I checked compression and got between 80 and 100psi Manual says 170psi so its more work than I thought. I am going to have engine rebored     I was thinking of just replacing rings but I think I will go the whole Hog. Bike has done 30K miles. I would like to thank Andrew for the very informative Manual he Emailed me. I have rebuilt a few Triumph engines in the past and would appreciate any Tips people have picked up in the past doing a 400 engine.

Trigger:
The only real thing you must watch out for on the 400's is the cam chain tensioner. 30K seems a bit low for a compression problem but, you will not know until you get inside.

Lobo:
Did you try a squirt of oil down the bores to check if the pressure 'recovers' on the compression test? If so, indeed likely the bores / rings, if it doesn't recover may be indicative of valve problems....

Simon

Orcade-Ian:
Did you have the throttles wide open when you did the compression test?  It makes a big difference if they are shut, as the cylinder has difficulty gulping enough air to actually compress.
Also, my spare 350/4 engine - which I'm using in the bike at the moment - had less than normal compression and I glaze busted the bores and used the original rings.  It doesn't use oil and now has a healthy compression.  This was a stop gap measure until I get the original unit back in but it is absolutely fine - I was out on it yesterday. 
As some of the others say, the cam chain tensioner is the part to rectify - but they are easily repairable as outlined in my article in the VJMC magazine.  Also many folk don't remove the rotor from the crank, saying it's OK to lift out the crank with it attached.  I never do it that way as you cannot then renew the crank seal on that end - having spent all of that time and money on gaskets alone, you could be spoiling the ship.
I am writing an article as we speak for the VJMC mag on the rebuild with pics of my original engine, and it will appear in full form on my web site too.

Hope you get sorted with your winter work,
Ian

AshimotoK0:
Keep it coming Ian (Orcadian) Sounds like you have got some good stuff to share with us there. Never joined the VJMC. Is it worthwhile doing so?
Anyone else got experience of being a member?

Cheers .. AshD

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