Topic: Cb350f fresh top end smoking like nuts!

[grcamna2]

Will you be redesigning the frame and welding new braces into it so it's as strong as you like ?

This really shouldn't be necessary since the motor is essentially the same specs as the original.

The lower frame around the engine has already been cut so welding is necessary anyway.

[jag767]

And I have to cut out more also. Then a lot is going back in yes. The motor will be used as a stressed member as well.

[grcamna2]

I'd like to see a thread on this project 

[jag767]

I'd like to see a thread on this project 

Heh i didnt make one because its not a 4. I can though.

[markreimer]

Very curious to here what you find out. i'm just waiting for space to open up in the shop so I can rebuild my '74 350F as well. let us know!

[grcamna2]

I'd like to see a thread on this project 

Heh i didnt make one because its not a 4. I can though.

Yeah,you could do one in the "Other Bikes" section 

[jag767]

Great, I will do so 

As for this problem. I just got off the phone with the machinist. He claims to be 100% positive the orings are there beyond any doubt. He also verified the valve to guide clearance. I am now at a complete loss

[markreimer]

Going out on a limb here, could you have forgotten those oil galley o-rings between the cylinder and head? I'm not super familiar with the 350F design as I have yet to open mine up, but I seem to recall there are high pressure oil feeders in there. That, or maybe the head gasket isn't sealing there? It can only be a few things I guess - oil gets past the rings, through the valve guides, or... in from between the block and head, right?

[jag767]

Going out on a limb here, could you have forgotten those oil galley o-rings between the cylinder and head? I'm not super familiar with the 350F design as I have yet to open mine up, but I seem to recall there are high pressure oil feeders in there. That, or maybe the head gasket isn't sealing there? It can only be a few things I guess - oil gets past the rings, through the valve guides, or... in from between the block and head, right?

Head gasket had a good seal, as can be seen where it delaminated onto the barrels removing it. All the gallery rubber is in. I am honestly at a complete loss right now.

[markreimer]

DId you do the leak down test yet? I'm not sure how else to proceed from here. So you've confirmed the rings were installed properly, with correct gap, valve guide clearance is within spec, guides/o-rings are in, hmm... and the piston to bore clearance is good too? Did the pistons show any signs of blow by?

[jag767]

I will do the leakdown tomorrow.

For the guys that asked about the frame on that other project, this will give you a vague idea of the plan.

[grcamna2]

I will do the leakdown tomorrow.

For the guys that asked about the frame on that other project, this will give you a vague idea of the plan.

The leak-down test would have needed to be done before the tear-down.

[jag767]

I will do the leakdown tomorrow.

For the guys that asked about the frame on that other project, this will give you a vague idea of the plan.

The leak-down test would have needed to be done before the tear-down.

There's an easy fix for that  . If I can't find anything else, then its not a big job to put it back together.

[grcamna2]

I will do the leakdown tomorrow.

For the guys that asked about the frame on that other project, this will give you a vague idea of the plan.

The leak-down test would have needed to be done before the tear-down.

There's an easy fix for that  . If I can't find anything else, then its not a big job to put it back together.

With a fresh head gasket. 

[scottly]

Head gasket had a good seal, as can be seen where it delaminated onto the barrels removing it. All the gallery rubber is in. I am honestly at a complete loss right now.

Have you slipped the cylinders off the pistons and inspected the rings yet? Someone recently had an issue with Cruzin rings that weren't up to spec:
http://forums.sohc4.net/index.php/topic,161003.0.html

[jag767]

Head gasket had a good seal, as can be seen where it delaminated onto the barrels removing it. All the gallery rubber is in. I am honestly at a complete loss right now.

Have you slipped the cylinders off the pistons and inspected the rings yet? Someone recently had an issue with Cruzin rings that weren't up to spec:
http://forums.sohc4.net/index.php/topic,161003.0.html

I measured end gap it was good.

[jag767]

I will do the leakdown tomorrow.

For the guys that asked about the frame on that other project, this will give you a vague idea of the plan.

The leak-down test would have needed to be done before the tear-down.

There's an easy fix for that  . If I can't find anything else, then its not a big job to put it back together.

With a fresh head gasket. 

Yep, I ordered a couple extra.

[nath180]

I will do the leakdown tomorrow.

For the guys that asked about the frame on that other project, this will give you a vague idea of the plan.

The leak-down test would have needed to be done before the tear-down.

There's an easy fix for that  . If I can't find anything else, then its not a big job to put it back together.

With a fresh head gasket. 

Yep, I ordered a couple extra.

Realise that I'm digging out an old thread but chasing a similar issue - what was the result of further investigation?

[markreimer]

nath - care to explain your issue?

I have a 350F that ran fine for about 30 miles, then turned into a massive smoke machine. #4 is full of oil, the other three are normal. I still haven't opened it up, but it's either the head gasket failing along the oil pressure line, or a broken ring. Hoping to find out this week or next. 

[SquierA]

Just joined this forum and have the exact same problem as jag767 had in 2016 with his 350F. Did anyone ever find the solution that could be shared here?

[markreimer]

Just joined this forum and have the exact same problem as jag767 had in 2016 with his 350F. Did anyone ever find the solution that could be shared here?

are you also using the cruizin image big bore kit? If so, as far as I know, you are hooped. I did three engine rebuilds with my 393cc kit and they all failed. I had two different machine shops verify the piston to bore clearance was correct. no oval/hour-glass shape to the bores. new valve guides, seals, etc.

When I'd pull the head off I'd find the pistons under a pool of fresh oil. Not just a bit...like a table spoon at least, maybe more. It went through a litre in under an hour. Oil spit out the pipe constantly. The CI rings are garbage.

I'd look for OEM Honda pistons and rings. If I still had the 350F, I'd have looked at using 400F pistons instead.

[SquierA]

Thanks for the reply Mark. Yes I am using a piston kit from CI however I went with 0.50 over size pistons instead of the big bore kit. The machine shop I use does great work and has bored several CB500/CB550 motors for me so I am confident his work is spot on. I did order a set of HONDA factory 0.50 over rings on ebay yesterday. In addition I remembered the machine shop calling me when they did the head work and said the valve stem seals wouldn't fit and it appeared the head did not use them. After a quick parts schematic search by me looking at the "valve" schematic I confirmed the valves did not use valve stem seals. After researching more yesterday and viewing the cylinder head schematic I was wrong and the head schematic shows valve stem seals are used on the intake and exhaust valves so I ordered a set today from 4into1 and a Lyle #36050 valve spring retainer tool so I can add the seals without taking the head off the bike. I did see several posts that some of the CB350F heads only had valve stem seals on the intake side. Do you have any info on this? Like I said the Honda factory cylinder head schematic shows both the intake and exhaust valves using seals. I appreciate any input you can provide.
 

[markreimer]

I think it depends which year 350F. I had a '74 and mine had valve stem seals on all 8 valve guides. But I have seen some heads where the exhaust guides had no seals. CB750's were the same I believe, maybe the F series, and 69, I can't remember exactly, but early models had no exhaust seals. That could cause some smoke at startup, but nothing like most of us 350F owners experienced. This was no puff of smoke, mine was more like a tire fire in the pipe.

I would say as long as your exhaust guides are the type that can accept seals, use em! No reason not to.

I hope those Honda rings fixes your issue, I'm really curious to hear about that, so please follow up with a report!

[SquierA]

Your input is consistent with what I read yesterday about some years using them on the exhaust side and some years not. I'm only doing the valve stem seals at this time and will let you know if that cures the smoking issue the bike has now. And yes it smokes really bad however not at all at start up. Once it warms up it is literally embarrassing to ride down the street. I will update as soon I have the valve stem seals installed.

[grcamna2]

Your input is consistent with what I read yesterday about some years using them on the exhaust side and some years not. I'm only doing the valve stem seals at this time and will let you know if that cures the smoking issue the bike has now. And yes it smokes really bad however not at all at start up. Once it warms up it is literally embarrassing to ride down the street. I will update as soon I have the valve stem seals installed.

What condition is your crankcase vent in ? I hope there is nothing obstructing that 'air way' so as to create pressure build-up inside your cases..