Hitchcocks Forum

a few threads ago I listed a concern after having climbed a steep hill with my newly rebuilt 350. as you may recall, it made a scheeching sound for a few seconds while climbing the hill, accompanied by a temporary loss of power. the bike has run fine since, but I'm concerned that there may be an issue with respect to the top end. how much compression should I have if I test it with a compression gage? plug looks fine, but I did notice a bit of oil consumption, but attributed that to the break in. don't want to open it up if the compression is good, but don't know what normal is. put an 8:1 piston in with the rebuild. may just be a bit paranoid.

I found that once having overheated the 350 that the rings where kaput. The key sign was the quickly blackened oil from blow by and on pulling the barrel off there were clear signs of gas escaping past the piston. I did the aluminium barrel upgrade and gave it new rings and it has been fine since. Whether iron or ali I tend to give bikes of this design vintage a full 1000 mile running in period. This helps stop the pinching up issue.

Looking from another angle could it have been clutch slip?

Hi Simon, I put a 570 together a while back and I said to the owner to take it for a ride around the block, which is about 10ks to see how it was running. He returned several hours later saying he had ridden it up into the hills, had put about 150ks on it and had used this bizare idea of rinning the rings in hard and fast. I nearly dropped to the floor in despair

Hi Dean, a 350 with reasonable compression should read around 110 psi on the gauge.

By the way - and still on this theme - did anyone notice the post yesterday about a newly build engine with alloy barrel being taken on the motorway at 60 - 65mph!

Simon said it was upgraded, not that it was newly-built. If you see his post on this topic, he recommends 1000 mile running-in periods.

I thought an up-grade happened when you fitted a new and better item.
Ah well - I got that wromg then.
Apologies to all.

the oil looks clean and the plug looks good. will check the compression - hopefully about 110 - if so, I will relax. my 350 easily does 60 to 65 on a flat without straining, after alloy cylinder, high compression piston and rings. will also look at the clutch - it is new as well and I guess it could have been the source of the noise - is there a break in for the clutch?

There is a school of thought that says you should run an engine in by giving it death for a short time before it gets the chance to get hot and seize. This is how the racing guys do it as they don't have the time to put 1000 miles on a new piston. My bitsa 350 was given 1000 gentle miles not exceeding 50 mph and never being loaded up hills. This was with a new barrel and a used piston with new rings. I'm not saying this is the only way but I do believe its the less risky. However, if your oil is clean and and the performance back to normal,then I'd leave we'll alone and enjoy.

can't imagine a 1000 mile break in period, as I only ride the bike for sport. guess I got away with one here, as the bike seems fine. compression tested out about 100. time to ride! thanks for the info.