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Discussion Starter #1
1970 CB350 runs pretty good, been riding it around. Sat for 2 years. Rebuilt carbs, new plugs, points, adjusted valves, timed. Did compression test, L - 155 R - 135 :( . Not good? Put some oil in right came up to 185. Where next?
Regards
Randy
 

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Sensei
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"1970 CB350 runs pretty good......"


Wait until you see how well it runs with good compression..... Re-ring time...
 

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agreed, top end rebuild is pretty easy if there is no cyclinder boring. plus you can put a new tensioner in there, lap valves and do the cyclinders. Its amazing how quiet these engines actually are with new parts inside. The parts are really cheap and you can source them from your honda dealership.
 

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If they are within tolerance, or no scaring. You can just get stock rings and hone the cyclinders so the rings will bed in.
 

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grab a flex hone from the interwebs, and the valve lapping kit from goodson, it has fine and coarse compound, and get a stick. and a valve spring compressor, sure you can get the valves out with a hammer and deep socket, but it's hard to get em back in that way. those tools will help you be less afraid of blowing up a motor, knowing that you can rebuild the top end in a night is nice. hit the cylinders with the flex hone real quick with some oil in there and wipe it down, if you notice vertical scratches in the walls, then you'll probably want to take it to a machinist and do a .25 overbore and fit oversize pistons and rings, that way you'll be working with fresh metal. there are some kits for 350 on ebay going for about $70, oversize pistons, rings and wristpins... good deal. spend a couple hundred bucks and you'll feel like you've got a brand new motor
 

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Discussion Starter #7
I'm starting to get it. Concerning the valve lapping, I'm not replacing the valves or seats, just lapping? And hoping (after honing) the cylinder walls have no scratches so I can use the old pistons with new rings. Of course I will need new gaskets. In case you haven't guessed this is my first engine tear down.

Found this video on lapping, just what I needed.

http://www.wonderhowto.com/how-to-lap-v ... 6527/view/
 

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This is what a destroyed cam chain tensionor looks like, the get super hard and just fall apart. This one broke the guide and locked the motor up. Luckily that probably saved the motor, but it ruined the head, it bugered up the guide holder beyond my welding skills.
 

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Discussion Starter #9
I'm convinced Doug350. Which parts would you replace? Tensioner - Guide - Roller - Push Bar
 

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It all depends on how far you want to go, splitting the cases is the easiest way to replace the chain. But its not a must if the chain looks good. you can tell alot about the chain by the cam gear. Replace the guide and the whole tensioer, there are 2 parts. Most of the spring loaded tensioers a good once you clean them. as for the hydraulic ones im not sure. Remember also you can put in a aftermarket tensionerand guide but there is a little clearancing to do, but they are made to last longer than the bike itself. As to lapping valves a buddy of mine showed me how to use a drill on low speed on the valve stem. Just be careful and listen for the high pitch of metal polishing metal, no grinding. Seats the valves really nicely.
 

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Discussion Starter #11
New Gage and test (2 times, same both times). 20 pounds difference, any need for concern? Lt 160 Rt 180 Guess that's why it runs pretty good. :oops:
 

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Honda "allows" 15 PSI max difference between cylinders ..... I DID notice your R cyl jumped up 45 PSI, while the left only "improved" by 5 PSI..... Is it possible that you are getting fuel in (that acts as a "seal"...or residual oil left from previous)? ...That's quite a jump.... Hopefully, that oil (and running it) just "freed-up" a sticking ring.....
IF you are happy with it...ride it.....But I'd recheck compression after another couple hundred miles.....Just on GP......
 

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Discussion Starter #13
Thanks, I did soak the Rt in Marvel Oil overnight, then rode it for 30 minutes. Now I'm soaking the Lt. Will let all know in a few days.
Regards
 
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