Topic: CB350F Valve Spec's

[silentsvn]

I was taking out my 350F this weekend when I noticed a "ticking". I turned back home after about 1/4 mile parked and ran the bike up a bit till I heard a dread clunk and the motor stopped.

Opened up the top end to find a cam follower snapped off and wedged up under another. I tore the top end down to find a smashed valve, busted cam shaft, scored pistons and nicked cylinder walls.

Here are some photos, i'm trying to figure out what to do at this point.

Looks like Ill be needing jugs, valves and pistons at minimum.

[iron_worker]

The damage doesn't look that bad. You could possibly just re-sleeve that one cylinder, however, then you run into the issue of having one "good" bore and the rest are worn.

If it's just nicks in the top of the piston you could probably just carefully smooth them out with some sandpaper to avoid any sharp edges.

I also don't see much wrong with that valve but that doesn't mean much. If it hit the piston then it most likely is bent. Have you measured to see if it is bent?

IW

[iron_worker]

Also, you definitely need to figure out the root cause of this problem. I'm guessing you might have a blocked oil passage somewhere which started the chain reaction melt down.

IW

[silentsvn]

Also, you definitely need to figure out the root cause of this problem. I'm guessing you might have a blocked oil passage somewhere which started the chain reaction melt down.

IW

I think it was the cam followers, there is oil in the head but it looks like there is a fracture on one followers that got lodged and then hell broke loose.

Here is the cam lobe that took the hit.



The valve on the #1 cylinder is cooked its sticking open about 3mm. So I guess at least that valve and guide will have to be replaced.



The other cylinders #1, #2, #4 all have the nicks in them as well and the scored pistons.



I would rather do it right, albeit expensive. I found a camshaft off eBay and a full set of followers so that should be taken care of.
1&2

3&4


#1 Piston


#4 Piston

[iron_worker]

The guide may be OK. It's likely the valve just bent at the neck and now won't fully return closed. However, now would be a good time to check the condition of the other guides and determine if you want to just do a full new set of guides and valves. (These "might as well" items get expensive quick ...  )

So you can either look for new sleeves but it's likely cheaper to just buy a used set of jugs that haven't been bored. Then you can bore 1st or 2nd size over and go with new pistons and rings. Or if you're really on the "might as well" train you can do a big bore kit for a very similar amount of money since you'd have to rebore anyway. 

Sorry about your luck but hopefully you can get it all sorted and running better than ever.

IW

[iron_worker]

I do find it odd that a rocker arm would let go though ... what seems more likely to me is that it was over revved and the valves floated into the pistons. Then maybe the piston slapped the valve back into the rocker which caused it to let go.

Just spitballin'!

IW

[silentsvn]

Ya I m not sure what happened I only revved it up to about 6K.

I m thinking that it might be best like you said to just find a set of used cylinders and get them bored over since 350F pistons are nonexistent.

I found these though $75 for Includes Piston, Rings, Wrist Pin

http://hondanuts.auctivacommerce.com/Piston-Kit-Honda-CB350F--P3947250.aspx#reviews

[silentsvn]

Digging a bit deeper I think I found the issue. The cam chain slipper is missing the locater on the tensioner arm so it had some play in it. This might have been the ticking and once I rev'd it up it might have jumped the cam sprocket.

#4 on the diagram.

[jas67]

Will 400F jugs and pistons bolt on?

[silentsvn]

Will 400F jugs and pistons bolt on?

I wish!

There are two bolts that need to be drilled for that to work from what I read on here.

I pulled the cylinders off and the pistons minus the scoring on the heads of seem okay and the rings are still good. Some of the scoring is rather close to the edge of the piston head as you can see on the #4 piston.


I'm worried about the nicks on the edges of the sleeves on the cylinders where it meets the head gasket and causing a leak or blow by.

 

 

[silentsvn]

Got back from machine shop and everything is okay with head except my valves are all too thin to grind.

Anyone have any good 350F valves? Searching Kibblewhite, DSS, eBay and all the other normal sites are returning nothing.

[sanxa_]

DSS has valves available

http://www.davidsilverspares.com/CB350-FOUR/part_39288/
http://www.davidsilverspares.com/CB350-FOUR/part_2913/

[silentsvn]

DSS has valves available

http://www.davidsilverspares.com/CB350-FOUR/part_39288/
http://www.davidsilverspares.com/CB350-FOUR/part_2913/

Ya way to expensive though for this motor. I cant justify $350 for it.

[iron_worker]

The cam chain jumping would definitely explain the valves hitting the piston ... 

If that's too much money for valves then you're probably stuck with trying to source used valves (likely you'll have to buy the whole head) and hoping they're in decent shape. It's a bit of a gamble though.

Something like this:

http://www.ebay.com/itm/Honda-CB350F-CB-350F-Used-Engine-Cylinder-Head-And-Valves-1972-M2-BDK-/151220477833?pt=Motorcycles_Parts_Accessories&hash=item2335715f89&vxp=mtr

IW

[sanxa_]

DSS has valves available

http://www.davidsilverspares.com/CB350-FOUR/part_39288/
http://www.davidsilverspares.com/CB350-FOUR/part_2913/

Ya way to expensive though for this motor. I cant justify $350 for it.

I feel you, I'm in the same boat with my bike looking for valves

[silentsvn]

Got my replacement rockers in today.

I noticed some have different stamping on them .12, .15, and .21

Do they need to match on each side or is it just from the castings?

[silentsvn]

Does anyone have full valve spec's for the CB350F

I have the service data which has most spec's for the valves but I'm looking for the valve assembly height and the seat pressure.

Mine are measuring at:

40-42lbs seat pressure
1.175" Assembled height

[iron_worker]

If you're just installing stock valve springs on a stock cam I don't think it's too critical to get the installed height and seat pressure just right.

IW

[silentsvn]

That's what I figured but the machinist I took the head too was asking - figured I would try to get him an answer.