Topic: Valve Lapping - Leak Test - Still leaking

[FeroxJB]

So.. I've lapped all the valves in the top end and put all the springs back on.. and after several LAPPINGS.. I can't get two of the exhaust valves to pass the leak test.

I'm pouring gasoline in the port with the head on it's side for the test..

It's not a huge amount.. just a small tidbit.. but almost immediately.

Any suggestions?

Should I consider buying new valve stems?

Also.. whenever I was cleaning them.. these two exhaust valves specifically had a lot of carbon build up on them.


76' CB 550F

[trueblue]

Sounds like you need to get the seats recut and the valves refaced

[FeroxJB]

Ugh! how much is this going to cost me?

[trueblue]

Ugh! how much is this going to cost me?

I cant comment on that in your neck of the woods but at the shop where I work it is about 15bucks per valve to face the valve and recut the seat

[faux fiddy]

Ugh! how much is this going to cost me?

I cant comment on that in your neck of the woods but at the shop where I work it is about 15bucks per valve to face the valve and recut the seat

That's pretty reasonable, It shouldn't be hard to find a friendly shop in Texas that would do the same.

I think there are jigs you can by for DIY, too.

[MoMo]

The angles of the cutters are very specific to each model of Honda, make sure that whoever you choose to do the work is familiar with Honda's.   15 is awfully cheap, we charged that per seat back in the  80's.  You could have a bent stem, guides would have nothing to do with fluid coming out at the seat...Larry

[trueblue]

The angles of the cutters are very specific to each model of Honda, make sure that whoever you choose to do the work is familiar with Honda's.   15 is awfully cheap, we charged that per seat back in the  80's.  You could have a bent stem, guides would have nothing to do with fluid coming out at the seat...Larry

We cant afford to be any dearer, we are a small shop in a town of about 25 thousand with 2 other engine shops in town so competition is pretty fierce, and honestly it only takes about 10 minutes per valve to do.

[MoMo]

[/quote] We cant afford to be any dearer, we are a small shop in a town of about 25 thousand with 2 other engine shops in town so competition is pretty fierce, and honestly it only takes about 10 minutes per valve to do.
[/quote]

That is refreshing honesty...Larry

[FeroxJB]

After much much lapping.. it seems like it all but stopped.. maybe a SMIDGE.. but nothing like it was. 

[faux fiddy]

I always say keep at it until you get hungry and have to go eat.

[MRieck]

The angles of the cutters are very specific to each model of Honda, make sure that whoever you choose to do the work is familiar with Honda's.   15 is awfully cheap, we charged that per seat back in the  80's.  You could have a bent stem, guides would have nothing to do with fluid coming out at the seat...Larry

I'll say. Most shops use a Serdi or something comparable.

[MCRider]

After much much lapping.. it seems like it all but stopped.. maybe a SMIDGE.. but nothing like it was. 

Are you lapping by hand or with the power drill method?

[OldSchool_IsCool]

A little trick I did that seemed to give a nice lap with reasonable effort was to use a conical spring (not much, a few Newtons should do it) and the T-handle from my tap set.  Insert the valve into the guide, a little lap compound on the face.  Spring over the stem, a little electrical tape on the stem where the T-handle clamps on.  The spring presses the valve to the seat.  finger-spin it clockwise for a bit, then counter-clockwise for a bit.  Fresh compound and repeat.

Gave me a nice even, dull gray band on the valve and seat in no time!

FYI, it is VERY important that the valves are lapped into the seat from which they came.  Don't mix valves between cylinders!!

[FeroxJB]

Its got a nice shiny band around the valve.  It still doesn't seat very well however.

[dave500]

i use rubber hose on the stem and pull it back with a varible speed drill slowly,changing  direction once or twice,counting ten each time.

[faux fiddy]

i use rubber hose on the stem and pull it back with a varible speed drill slowly,changing  direction once or twice,counting ten each time.

I like to just use my hand. After a few turns back and forth you can feel that the paste is just sliding instead of cutting. I like to be able to feel some grit doing it's thing, and just spinning with a smooth feeling probably doesn't do as much.

Amd there are different grits of valve grind solution, I'm sure you know...

[srook]

Lapping is not a cure all and no substitute for a valve job.  Your exhaust valves probably have pitting and if so all the lapping in the world won't allow them to seal.  I would suggest getting new valves as well.  I am also into classic British bikes and no one in the Brit bike world lapps valves or if they do they keep it a secret.  I think it has to do with the initial cost of ownership being lower for Japanese bikes.  Ask yourself why you are rebuilding the motor?  If you want to build a reliable engine that runs like it should then put the lapping sticks and compound away and get a valve job.  Yes it costs money and I would probably insist it was a serdi valve job.  Not trying to sound harsh but do it right the first time or do it over again, your choice.
Scott

[MCRider]

i use rubber hose on the stem and pull it back with a varible speed drill slowly,changing  direction once or twice,counting ten each time.

That's the ticket in my mind. That should make quick work of it. Now, if the stem to guide clearance is too high, you may have a situation where you're not going to get a consistent seal without new guides. That's a different issue from the efficacy of lapping which should work fine if the guides are OK.

With the drill you can feather the pressure on the grinding compound to whatever degree you want.

If you need guides, you'll need a valve job.

[MRieck]

So.. I've lapped all the valves in the top end and put all the springs back on.. and after several LAPPINGS.. I can't get two of the exhaust valves to pass the leak test.

I'm pouring gasoline in the port with the head on it's side for the test..

It's not a huge amount.. just a small tidbit.. but almost immediately.

Any suggestions?

Should I consider buying new valve stems (seals)

Also.. whenever I was cleaning them.. these two exhaust valves specifically had a lot of carbon build up on them.


76' CB 550F

Huh?

[faux fiddy]

Lapping is not a cure all and no substitute for a valve job.  Your exhaust valves probably have pitting and if so all the lapping in the world won't allow them to seal.  I would suggest getting new valves as well.  I am also into classic British bikes and no one in the Brit bike world lapps valves or if they do they keep it a secret.  I think it has to do with the initial cost of ownership being lower for Japanese bikes.  Ask yourself why you are rebuilding the motor?  If you want to build a reliable engine that runs like it should then put the lapping sticks and compound away and get a valve job.  Yes it costs money and I would probably insist it was a serdi valve job.  Not trying to sound harsh but do it right the first time or do it over again, your choice.
Scott

I figure if i'm in the motor because the rings were stuck an the valves look good, the valves are going to  get lapped in while it's apart. And you are accurate abut the initial investment ,too. A valve job would have cost more than the bike I was working on.

[FeroxJB]

Decided to go ahead and have it done at the shop.

I dropped it off at the machine shop a few days ago.  I should be getting it back this coming week.

[camelman]

You should definitely replace any valve stem seals before you reassemble.

Camelman