Topic: How bad are these valves?

[Sdsbassist]

Cb550f motor.

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[HondaMan]

It looks like the exhaust valves are leaking quite a bit. Check the valve guides, too, as too much looseness there can caused overheated valves, charring their sealing faces and making them leak - like these are doing.

[bryanj]

Whatever they need to come out before a decent opinion can be given

[ekpent]

 Quick easy test is to put the plugs back in and lay the head flat and fill the chambers with a thin liquid and see which one are the leakers. Clean-up and a good lapping if needed is not overly difficult once you get the correct paste etc..

[PeWe]

Seats might be pitted in need of 3 angle cut. Valves might wobble sideways when they are around 8-9 mm out. Dirty valves does not matter, oil due to leaking o-rings gasket or whatever. Valves seat surfaces can be completely worn out, concave surface against seat.
Guesses about what NOT shown on those photos.

[Jessamine]

Whatever they need to come out before a decent opinion can be given

Agreed. A simple tool for pulling these valves can be made for under $10, with a 6" C Clamp and a deep socket with a cut out of the side to allow access to the valve spring clips. Easy to have a look at the seats then.

1975 CB750F
1986 CN250
2005 KLR650

[754]

You can lap them if they are not badly worn, but nothing beats agood 3 angle valve job..

[Sdsbassist]

Cool! Got all that stuff already. Can you send a link or pic of the tool?

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[CarbonK]

Cool! Got all that stuff already. Can you send a link or pic of the tool?

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You could also use a piece of pvc instead of a socket.

[Jessamine]

Cool! Got all that stuff already. Can you send a link or pic of the tool?

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Here's the one I whipped up-- IIRC I used a 21mm socket.  Not sure if it matters, but I stuck a microfiber cloth over the valve face so the other end wouldn't mar it.

1975 CB750F
1986 CN250
2005 KLR650

[uksparky]

Springs are recessed in the head you need this tool..i got it works great

https://www.ebay.com/itm/Valve-Spring-Clamps-Compressor-10-PCS-Cars-Motorcycle-Tool-Bit-Set-OHV-OHC-Kit/263737849282?epid=18020148455&hash=item3d68003

[dave500]

roll up a ball of cloth in the combustion chamber and rest the head on it so the valves cant open,place another rag over the valve you want to remove,place a suitable socket on the retainer and whack it,itll come apart with the collets trapped in the rag,of course youll need a proper compressor tool to reinstall them.

[Jessamine]

roll up a ball of cloth in the combustion chamber and rest the head on it so the valves cant open,place another rag over the valve you want to remove,place a suitable socket on the retainer and whack it,itll come apart with the collets trapped in the rag,of course youll need a proper compressor tool to reinstall them.

Y i k e s

1975 CB750F
1986 CN250
2005 KLR650

[dave500]

been doing that for years,never had any yikes moments.

[Joao_f3rr3ira]

I'm rebuilding my F2's head and I had the same problem.
The intake valves on cylinders 1 and 2 were leaking and one valve guide was cracked on cylinder 2.
In my opinion, the best way to check is to bolt the spark plugs with the valves still in place, turn the head with the chambers facing up, apply some petrol on the chambers and observe if any liquid is falling from either the intake or exhaust ports. If yes then you can try to lap them, if it still doesn't work you will need a 3 cut valve job.

Now since we are discussing this issue, when I took my valves out (I also use a simple C clamp with an adapted socket as my spring compressor tool) I discovered that the exhaust valve in cylinder 4 was badly damage close to the top notch like if someone touched with an angle grinder on it. My new valve guides are already in place and were reamed. Do I have to replace all four valves now or can I just replace the bad valve for a brand new one?

Thanks

[70CB750]

roll up a ball of cloth in the combustion chamber and rest the head on it so the valves cant open,place another rag over the valve you want to remove,place a suitable socket on the retainer and whack it,itll come apart with the collets trapped in the rag,of course youll need a proper compressor tool to reinstall them.

Yeah, tried that too.  Still prefer a compressor or - as Frank suggested once - milling machine works well.

[754]

It was drill press actually or mill.
 If you lap and your guides are worn, it may not seal long, or well at all..less power.

To the last guestion..
If you have a bad valve replace it, the other may be ok. 

I should mention if some of you are getting valves ground, you cannot take much off the stem... which they may automatically do if you don't specify.
 My current motor needs constant valve adjustments and I suspect rapid stem wear.

[Joao_f3rr3ira]

That's what I thought but the place where I get my parts from was suggesting to change all four, thanks.

If it helps, what I did to check for valve leaks was also:
- Measure the contact surface of the valve with the seat itself. In my case all of them were ok, if not the only way to fix it would be to replace the valve(s).
- Measure the clearance between the guide and the valve with a dial and check the tolerance on the manual.
- Observe if the valve seats uniformly, if not then I think only a 3 cut job will do it.

Thanks

[krusty]

been doing that for years,never had any yikes moments.

Same here, it always works no yikes.
For replacing I made up a resin copy of the combustion chamber and, with head flat on the bench I would use a ring spanner to compress the valve while friend or wife would slip the collets in.

[dave500]

i just happen to be assembling one now,standard over centre tool with adaptor fork I made up,you can get around the whole stem without futzing through a slot cutout of a socket.

[dave500]

a good pair of offset/bent tweezers are handy,just makes it all too easy.

[dave500]

once the tool is released and the valve spring pressure is applied rap the stem three or four times enough to lift the valve off its seat with a brass drift,be carefull not to knock the retaining cap,that's how you remove them!without yikes!

[seanbarney41]

brass punch is motorcycle mechanic's best friend

[dave500]

and a copper hammer.

[seanbarney41]

Maxwell's copper hammer?...