[jonathankindler]

I need professional advice.

I bought this beautiful cb 350, with 7ooo miles on it, changed the tires, synced the carbs and it ran great except for in 5th gear, and it would begin to bog down around 70 mph. I was getting on the highway and it began to bog so I let off a bit, as I did that I heard a noise from the engine then white smoke started billowing from my right exhaust pipe. I'm not to sure if the bogging down had to do with this problem now, but I'm wondering if any one has any advice to what the problem could be.

I checked my oil, all good there. I check my compression on that cylinder, there isn't any. I'm thinking that I blew a piston ring. Does this sound right to anyone else, and if so, has anyone had experience on changing these out?

 

[KeithTurk]

You've hurt that hole.. that's fairly sure....

you can put some oil in the cylinder and see if it marginally raises the compression... ( the oil will seal the rings momentarily )

If it raises it, then it's normally a valve seal issue...

K

 

[WintrSol]

Bad news. You could have eaten a valve on that side; before trying to run it again, take the valve covers off and look to see if they're working properly when hand turning the engine.

 

[jonathankindler]

So I found out that I blew a whole in my piston, you can see the hole if you take out the spark plug. both the intake and exhaust valves seem fine.

Anyone know where I can get cheap pistons for a 72 honda cb350 twin? thanks.

 

[HondaIlya]

ebay

 

[Easy Rider 2]

both the intake and exhaust valves seem fine.

Based on what ?? You need to get the head off before you go buying parts.
Piston domes don't usually just fall apart without some "help".

 

[Munkey990]

Based on what ?? You need to get the head off before you go buying parts.
Piston domes don't usually just fall apart without some "help".

I agree. I've never seen a piston just "blow a hole". Something caused the hole. Timing could have jumped causing the valve to get too friendly with the piston. Broken valve keeper or spring could cause a valve to drop into the combustion chamber. I guess extreme over heating could cause a piston to just melt but that's a long shot.

 

[RonnieJ]

I agree with dont buy parts yet, pull the engine and remove the head, you could have a valve seal or rings.

 

[CrystalCanole]

I agree take apart first and have a look.

 

[Gobblerforge]

Did you get the head off yet and what did you find?
Gobbler

 

[pizzaman]

I'll join the croud.....strip it down and see what the damage is...then look for the cause.
Lastly....buy parts.

 

[apbbnbanb_07]

Whats the top speed on your bike anyways? I've got a 72 CL350 and she tops out at 70, let alone trying to push it past that.

 

[hbw0014]

smoke

rings maybe? or you are getting so much gas burnt up in the chamber.

 

[Slinkyguitarist]

ewww! looks like we got a rebuild job here.

 

[Wombatunderground]

Whats the top speed on your bike anyways? I've got a 72 CL350 and she tops out at 70, let alone trying to push it past that.

I've got a cb350 k3 which has apparently done 90mph. Being a new rider the fastest I've had it is 50.... That's if the speedo is accurate :-D

The previous owner apparently had it up to 90mph.

To the OP, Bugger, Hopefully it's not too bad but there seems to be a lot of experience here saying otherwise. Fingers crossed for you man.