cb350 head gasket issue
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Scott,
Dude, that's a fucked up cylinder. Don't think you want to use that again. My guess is that the oil leak forced it's way under the gasket and then allow blow by to destroy the gasket.
Get another set of cylinders, some new rings, and if the pistons are good send the cylinder down to langcourt with the pistons and have them bore them to fit. Install the new rings and you are ready to go.
I once forgot the orings myself. Created a leak but not a real bad one...bad enough that I pulled the head at the track but it wasn't spewing out or anything. I had a solid copper gasket at the time so I didn't have the same issues you did. Those knock pins are a must, besides locating the head properly they give the oring a place to seal against and stay in shape.
Easy enough fix if you get on the ball and get it done. Getting cylinders properly bored by real professionals like Langcourt Cylinder Technologies is real important in my book. Lots of people like to get them done at the local machine shop...but these are race bikes not street bikes. They need the extra precision. It can probably add a year to the racing lifespan of a ring set and provide more power to boot.
JohnnyB
Dude, that's a fucked up cylinder. Don't think you want to use that again. My guess is that the oil leak forced it's way under the gasket and then allow blow by to destroy the gasket.
Get another set of cylinders, some new rings, and if the pistons are good send the cylinder down to langcourt with the pistons and have them bore them to fit. Install the new rings and you are ready to go.
I once forgot the orings myself. Created a leak but not a real bad one...bad enough that I pulled the head at the track but it wasn't spewing out or anything. I had a solid copper gasket at the time so I didn't have the same issues you did. Those knock pins are a must, besides locating the head properly they give the oring a place to seal against and stay in shape.
Easy enough fix if you get on the ball and get it done. Getting cylinders properly bored by real professionals like Langcourt Cylinder Technologies is real important in my book. Lots of people like to get them done at the local machine shop...but these are race bikes not street bikes. They need the extra precision. It can probably add a year to the racing lifespan of a ring set and provide more power to boot.
JohnnyB
OK, But i am still wondering. What hapened first. the oil leaked into the head causing the gasket to fly, or did the gasket fly causing the oil to fling?
I have jugs, so does she. When I am finished putting the engine back together, I'll weigh it all by tiself.
scott
I have jugs, so does she. When I am finished putting the engine back together, I'll weigh it all by tiself.
scott
Scott,
That's a hard call. I wouldn't think oil pressure is high enough to force it's way through the gasket to cylinder which half the time is at a much higher pressure anyway.
Might have been a flaw in the gasket, a kink or something in the sealing band. Probably would have blown regardless if you had the knock pins and and oring in. Just with the knock pin in it would have blown a lot less oil...the oring would have been destroyed by the hot gasses leaking out.
When you put it back together try to use a quality gasket, and of course install the knock pins and orings...and you might want to check that stud when you torque it, if it feels spongy it might be going bad.
Do you do the trick of loosening a head nut to check for oil flow when you first start a new engine? Just wondering....maybe it didn't get torqued back down.
JohnnyB
That's a hard call. I wouldn't think oil pressure is high enough to force it's way through the gasket to cylinder which half the time is at a much higher pressure anyway.
Might have been a flaw in the gasket, a kink or something in the sealing band. Probably would have blown regardless if you had the knock pins and and oring in. Just with the knock pin in it would have blown a lot less oil...the oring would have been destroyed by the hot gasses leaking out.
When you put it back together try to use a quality gasket, and of course install the knock pins and orings...and you might want to check that stud when you torque it, if it feels spongy it might be going bad.
Do you do the trick of loosening a head nut to check for oil flow when you first start a new engine? Just wondering....maybe it didn't get torqued back down.
JohnnyB
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10,189 Posts
scott,
i use the vesrah gaskets and have had no problems with my head leaking. my problem is exhaust parts falling off. i think i'm gonna attach a big magnet to my seat so i guess that will help.
if you need the vesrah part #, let me know! any motorcycle shop that can buy off parts unlimited can order it.
tex
p.s.- no joe, using a vesrah gasket is not cheating. buying gaskets from honda is stooopid!
i use the vesrah gaskets and have had no problems with my head leaking. my problem is exhaust parts falling off. i think i'm gonna attach a big magnet to my seat so i guess that will help.
if you need the vesrah part #, let me know! any motorcycle shop that can buy off parts unlimited can order it.
tex
p.s.- no joe, using a vesrah gasket is not cheating. buying gaskets from honda is stooopid!
Sure, send along the part no. 1mm over if you have it.
scott
thanks for the replies.
ps, the studs and the torquing were ok, I was just kidding. But my original question still unanswered is, did the gasket get installed upside down? Again, I put the smaller band of metal down.
scott
thanks for the replies.
ps, the studs and the torquing were ok, I was just kidding. But my original question still unanswered is, did the gasket get installed upside down? Again, I put the smaller band of metal down.
I don't think you can install it upside down. The knockpins and other holes wouldn't align as it isn't symetrical.quotes, the studs and the torquing were ok, I was just kidding. But my original question still unanswered is, did the gasket get installed upside down? Again, I put the smaller band of metal down.
I think.
I've used the Vesrah stuff and never had a problem with it.
As for upside down....didn't know there was one
In many cases Rob is right...they aren't exactly symetrical so it only goes on one way....don't know about the 350 though.
I only use Cometic CFM-20 gaskets anyway...but about $40 a pop. They are however very very good.
I'm trying to come up with a reason the small or large band should be up or down....but I can't. I could make something up if you want.
If you can find Athena gaskets to fit a CB350...use them, they are freakin excellent...and the OEM maker for most Euro bikes. They make them for the vert 175's but not the slopers. About the same price as Vesrah...maybe a tad more.
JohnnyB
As for upside down....didn't know there was one
In many cases Rob is right...they aren't exactly symetrical so it only goes on one way....don't know about the 350 though.
I only use Cometic CFM-20 gaskets anyway...but about $40 a pop. They are however very very good.
I'm trying to come up with a reason the small or large band should be up or down....but I can't. I could make something up if you want.
If you can find Athena gaskets to fit a CB350...use them, they are freakin excellent...and the OEM maker for most Euro bikes. They make them for the vert 175's but not the slopers. About the same price as Vesrah...maybe a tad more.
JohnnyB
More details. I can't find a good detailed drawing of this, so here goes.
1. The head gasket is symmetrical.
2. The knock pins on the top of the jugs ONLY go on the forward outboard studs, as there is a "landing" set into both the top of the barrels and the bottom of the head for the pins to go into. The knock pins, which are all the same size, are too large a diameter to go into the rear outboard holes, which, again, have no landing for them to set on, therefore, they would go into the head/cases with no place to stop them.
3. On the TOP of the HEAD, there are two stepped holes, to locate two knock pins, but they are on the REAR outboard studs.
4. I noticed that I put the little rubber o rings on the studs to go INTO the knock pins between the head and jugs. OOpps. was this my error? I was sure that the oil supply/oil return was through the REAR studs. It is odd, though that the knock pins are between the front suds on the top of the jugs and on the rear studs on the TOP of the head, not on the front studs.
Any of this make sense? What I really need, I guess, is a detail as to the installation of the head. (and I do not know wha t is located under the barrels, as I have not removed them yet. i am going to try and salvage these for the moment. I can easily look into it, though, by lifting the head a bit. I know, jb, bad move, but i think it'll work.) So . . . Where do the knock pins go, where do the little rubber orings go, and why is this head diffferent, if it is? Or did I do all of this right and I had a bad head gasket.
And am I correct as to the oil supply/return route?
Scott
Edited by - imslow on Mar 22 2005 09:16:35 AM
1. The head gasket is symmetrical.
2. The knock pins on the top of the jugs ONLY go on the forward outboard studs, as there is a "landing" set into both the top of the barrels and the bottom of the head for the pins to go into. The knock pins, which are all the same size, are too large a diameter to go into the rear outboard holes, which, again, have no landing for them to set on, therefore, they would go into the head/cases with no place to stop them.
3. On the TOP of the HEAD, there are two stepped holes, to locate two knock pins, but they are on the REAR outboard studs.
4. I noticed that I put the little rubber o rings on the studs to go INTO the knock pins between the head and jugs. OOpps. was this my error? I was sure that the oil supply/oil return was through the REAR studs. It is odd, though that the knock pins are between the front suds on the top of the jugs and on the rear studs on the TOP of the head, not on the front studs.
Any of this make sense? What I really need, I guess, is a detail as to the installation of the head. (and I do not know wha t is located under the barrels, as I have not removed them yet. i am going to try and salvage these for the moment. I can easily look into it, though, by lifting the head a bit. I know, jb, bad move, but i think it'll work.) So . . . Where do the knock pins go, where do the little rubber orings go, and why is this head diffferent, if it is? Or did I do all of this right and I had a bad head gasket.
And am I correct as to the oil supply/return route?
Scott
Edited by - imslow on Mar 22 2005 09:16:35 AM
Scott...you've got the head on backwards!!
Wow...
Ok...first of all, oil supply is up through two outboard studs...on the 175's it's the rear studs. The oil drains back through the cam chain tunnel.
The green orings are located on the studs through which the oil supply flows. In NO case whatsoever should the orings go between a knock pin and a stud....if that is done on the oil supply studs it will block the oil flow to the head.
Now...look at the head gasket. The four inner stud holes should be the same size. Either two, or all four of the outer stud holes are going to be larger. The Knock pins will go on the outer studs...which ever studs have a landing on both head and jug. Ok...now you should be left with two outer studs holes that seem to have extra clearance about them...that is typically where the oil suppy comes from. The gasket holes in these locations should be large enough to accomodate the orings.
Do you have a service manual for this bike? Or a parts book? What will answer most of your questions is which studs are used for the oil supply....those studs must have the orings. If those studs also have landings for the knock pins then the orings are installed OUTSIDE the knock pins. If the oil supply studs have NO landings for knock pins then the oring just gets placed inside the hole in the gasket that surrounds the stud.
175's have four knock pins in the head/jug-top, one on each outside corner. You can spot which studs are the oil supply studs by lifting up the jugs...look at where the studs come out of the engine case...you will see that two studs have a tear dropped shaped cavity that connects the stud passage to an oil passage. Look for the same setup on the 350 to locate the oil supply studs.
The reason there are only two knock pins on the bottom of the jugs is that that if they were used on the oil passage studs it would block the flow from the tear drop cavity to the stud passage.
This make sense?
JohnnyB
Wow...
Ok...first of all, oil supply is up through two outboard studs...on the 175's it's the rear studs. The oil drains back through the cam chain tunnel.
The green orings are located on the studs through which the oil supply flows. In NO case whatsoever should the orings go between a knock pin and a stud....if that is done on the oil supply studs it will block the oil flow to the head.
Now...look at the head gasket. The four inner stud holes should be the same size. Either two, or all four of the outer stud holes are going to be larger. The Knock pins will go on the outer studs...which ever studs have a landing on both head and jug. Ok...now you should be left with two outer studs holes that seem to have extra clearance about them...that is typically where the oil suppy comes from. The gasket holes in these locations should be large enough to accomodate the orings.
Do you have a service manual for this bike? Or a parts book? What will answer most of your questions is which studs are used for the oil supply....those studs must have the orings. If those studs also have landings for the knock pins then the orings are installed OUTSIDE the knock pins. If the oil supply studs have NO landings for knock pins then the oring just gets placed inside the hole in the gasket that surrounds the stud.
175's have four knock pins in the head/jug-top, one on each outside corner. You can spot which studs are the oil supply studs by lifting up the jugs...look at where the studs come out of the engine case...you will see that two studs have a tear dropped shaped cavity that connects the stud passage to an oil passage. Look for the same setup on the 350 to locate the oil supply studs.
The reason there are only two knock pins on the bottom of the jugs is that that if they were used on the oil passage studs it would block the flow from the tear drop cavity to the stud passage.
This make sense?
JohnnyB
You've got the head on backwards . . . well, I did think abou tthat for a second when Iooked at it. Bwahahah.
OK, there's the rub. I did NOT put orings in between the head gasket where there are the studs that have larger bores (outboard) but do not accomodate knock pins. That's where the head gasket blew, probably due to oil being pulled into the cylinder from the non gasketed supply from vacuum and being burned.
I do have a manual, but it is buried with every other thing I am still looking for since moving. i found the 450 manual, but that engine layout is different. i'll find it.
thanks again
S
OK, there's the rub. I did NOT put orings in between the head gasket where there are the studs that have larger bores (outboard) but do not accomodate knock pins. That's where the head gasket blew, probably due to oil being pulled into the cylinder from the non gasketed supply from vacuum and being burned.
I do have a manual, but it is buried with every other thing I am still looking for since moving. i found the 450 manual, but that engine layout is different. i'll find it.
thanks again
S
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2,006 Posts
Scott
The oil drain is down the rear studs and directly into the galley above the oil pump and it also dribbles into the crank bearings. I've got one apart on the bench at home so I hope I'm remebering it correctly.
I looked at my parts manual last night because I didn't remember ever putting o rings anywhere in the top end except the around the cylinder spigots and they're huge. I think those green o rings are the seals for the rocker arm excentric adjusters. Some of the motors have had blue rubber goomers on the outside front studs about a third of the way up from the bottom. Don't know why they aren't on all of them. They are soft, even after 30 years, and fall off in the parts washer. Perhaps a vibration damper?
bfd
The oil drain is down the rear studs and directly into the galley above the oil pump and it also dribbles into the crank bearings. I've got one apart on the bench at home so I hope I'm remebering it correctly.
I looked at my parts manual last night because I didn't remember ever putting o rings anywhere in the top end except the around the cylinder spigots and they're huge. I think those green o rings are the seals for the rocker arm excentric adjusters. Some of the motors have had blue rubber goomers on the outside front studs about a third of the way up from the bottom. Don't know why they aren't on all of them. They are soft, even after 30 years, and fall off in the parts washer. Perhaps a vibration damper?
bfd
Bill, I do not remember ever having to take off orings when I rebuild/take apart these things (I have disassembled three 350s now) as far as I can re-call, which is getting harder these days. But I can't see anything wrong with putting them in. I thougt, though, that there were black orings that were for the rocker adjusters, not the green ones.
scott
scott
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2,006 Posts
Scott
I just couldn't recall any place o rings would go in relation to the cylinder studs. I was looking at the parts manual last night figuring I'd been leaving out something important. I'll look again if it would help you. I'm curious anyway.
The orings are probably all black ones. I saw some green ones in my gasket drawer- maybe those were 175 parts.
bfd
I just couldn't recall any place o rings would go in relation to the cylinder studs. I was looking at the parts manual last night figuring I'd been leaving out something important. I'll look again if it would help you. I'm curious anyway.
The orings are probably all black ones. I saw some green ones in my gasket drawer- maybe those were 175 parts.
bfd
Don't want to disagree with Bill but....
Oil drain back is through the cam chain tunnel...oil suppy from the main gallery feeds the cam bearings and cam lobes. Note the oil drain passages down by the base of the exhaust springs that leads to the chain tunnel. The oil galley above the oil pump should be the main supply galley....it feeds the main bearings under pressure...there is a connection from this main galley to the two outboard feed studs, from there it travels to the top end. Where the main galley feeds into the studs you should see small restrictor holes, these control the pressure feed to the top end. For the oil to drain back through the rear studs the head would have to have oil about and inch deep in it.
Remember...oil doesn't drain into the pump...it's pulled up from the sump and pumped into the main gallery. First the main bearings get fed, then there is a small feed to the gear box shafts, and then it feeds up the studs to the top end. The main bearings receive probably 70% of the total oil flow.
Usually the factory service manuals have a nice oil flow diagram somewhere.
On a 175 the main oil gallery is at the base of the rear studs, and feeds up through the two rear outboard studs.
JohnnyB
Oil drain back is through the cam chain tunnel...oil suppy from the main gallery feeds the cam bearings and cam lobes. Note the oil drain passages down by the base of the exhaust springs that leads to the chain tunnel. The oil galley above the oil pump should be the main supply galley....it feeds the main bearings under pressure...there is a connection from this main galley to the two outboard feed studs, from there it travels to the top end. Where the main galley feeds into the studs you should see small restrictor holes, these control the pressure feed to the top end. For the oil to drain back through the rear studs the head would have to have oil about and inch deep in it.
Remember...oil doesn't drain into the pump...it's pulled up from the sump and pumped into the main gallery. First the main bearings get fed, then there is a small feed to the gear box shafts, and then it feeds up the studs to the top end. The main bearings receive probably 70% of the total oil flow.
Usually the factory service manuals have a nice oil flow diagram somewhere.
On a 175 the main oil gallery is at the base of the rear studs, and feeds up through the two rear outboard studs.
JohnnyB
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2,006 Posts
Thanks for the clarification JohnnyB, you are right on as usual
I double cheecked the parts book again and couldn't find any o rings used in relation to the studs. I'd be concerned with choking oil supply to the top. A couple of motors I've disassembled have had cams a blue/black color from heat and discoloration on the rocker arms. Oil supply problem?
Scott (or any CB350 guys)
I was considering drilling and safety wiring the cam sprocket bolts to prevent them backing out. It's never happened to me before but Matt T had it happen a couple of times.
It would be easy to do now while the motor is out. Can you see a downside?
bfd
I double cheecked the parts book again and couldn't find any o rings used in relation to the studs. I'd be concerned with choking oil supply to the top. A couple of motors I've disassembled have had cams a blue/black color from heat and discoloration on the rocker arms. Oil supply problem?
Scott (or any CB350 guys)
I was considering drilling and safety wiring the cam sprocket bolts to prevent them backing out. It's never happened to me before but Matt T had it happen a couple of times.
It would be easy to do now while the motor is out. Can you see a downside?
bfd
i just torque mine to spec. then some medium lock tite. and make sureyou put the correct ones in the correct holes or you'll be screwed, but im sure you know that. screwing around with all of the 350 stuff i have, ive never seen that happen to anyone buy matt. and 2x to boot. so i think he was just doing something wrong. i dont think it'd hurt anything, but i just dont bother.
me
me
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