Topic: How bad does this look? 1973 cb350f

[treemagnet]

Hello All.               

I'm new here and have been lurking for some time but finally decided to get into this project.  I look forward to hanging out here and learning a thing or two. I'll document all progress.

My plan was to take the top end off so that I could order a time-sert or Helicoil to repair the mis-sized spark plug that the PO somehow "threaded" in there. Once i had the top end off - it looked worse than i expected, although I'm not sure what i expected of a 1973. All told it probably looks about average. The valves are caked with carbon, as are the top of the pistons. The cylinders do not seem to be scored or scratched badly. My question is - where do i go from here? I have a dremmel or wire brish but do not want to ruin the valves seats. I sprayed with a liberal amount of carb cleaner and brushed with a nylon bristle brush so far - until further instruction.
Please note that piston one was dry as a bone while the other 3 are quite wet - what does this tell me?

I'm not interested in investing in new valves/springs etc unless absolutely needed. This will be my first time going this far in the engine and i bought this bike to learn how to work on bike more proficiently. I have been messing with it for 2 years and have finally decided to get it running well - if possible.....



Cam Lobes:


After light cleaning:


Dry Piston:



Thanks guys. Obviously i would be more than happy to take more specific pics if it would be more telling of the potential this engine has. I just want a runner/DD not looking for anything crazy or to spend a boat load of money on this project. I have an ideal project that involves a cb400f but for now the 350f will have to do.

BTW - Just reviewed my post to find that these pics were not full sized. It's too late tonight to figure that one out. I'll fix it tomorrow if i need to - sorry - I'm a newb.....
thanks!

[bryanj]

Pictures too small to tell, if it turns over and the valve seats hold fluid (paraffin down the inlet/exhaust holes and see if it leaks to the combustion chamber) should be OK

[treemagnet]

i'll try to put the parafin in there and see if i have seepage. I have some stuff called Benzine/Naptha that i have used for this before.
thanks

[mattcb350f]

That actually looks quite normal...at least as far as I can tell from squinting at the wee pics.

The carbon build is isn't really the issue, but rather the amount of wear on the metal.

Have somebody measure the cylinder bores to see how much wear is there. It may be that I doesn't need rebuilt at all. While the head is off however, I would suggest at least having the valves and seats re-ground and putting in new seals. This is a rather routine job for the average engine/motorcycle shop but specific tools are required.

Have a close look at the rocker arms. The 350F's were prone to the hardness wearing or chipping off which leads to rapid cam wear. I had this problem and ended up replacing about 4 or 5 rocker arms as well as the cam. The good thing is if you have to replace the cam....put a lumpier one in and get more power 

 Matt.