Club 80-90 Forums

The internet left me baffled. Far too many contradictory and overly-long clips.
So please save my day by checking out the new valve lapping photo using fine paste only. The valve seats are free of carbon, too.
On the valve l can see rings in the lapping . Apparently that is not good. So does this mean too much pressure on the stick or not enough? Or more of the same will eradicate lines?
I'm aware the lapped area should be between 1.4 to 2.5mm deep on the valve. At present it is just under 2mm (technical stuff, eh?) , and that's about as deep as l would like to go.
I am oil lubricating the valve guide to prevent scratches.

Thanks and regards,

Exhaust cylinder 1 valve seat.



Matching exhaust valve. Sorry, really hard to photo with my naff android phone.

Are you lapping by hand or machine? When lapping I was always taught to lift and rotate often to avoid concentric rings. A light spring under the valve gives lift to help you do this.

Coarse paste will always do that, once you have a full seat witness go again with some fine paste. Running in will soon smooth it off!

Oldiebut goodie wrote: ↑31 Dec 2024, 14:30 Are you lapping by hand or machine? When lapping I was always taught to lift and rotate often to avoid concentric rings. A light spring under the valve gives lift to help you do this.

By hand with wooden post and rubber sucker. Ten times back and forth. Then rotate 90 degrees and repeat the three more times. Clean off and inspect. I have repeated this procedure three times. I'm not pushing whatsoever. Just letting weight of tool do the work.

silverbullet wrote: ↑31 Dec 2024, 15:21 Coarse paste will always do that, once you have a full seat witness go again with some fine paste. Running in will soon smooth it off!

As the valves are new and seat are nice and shiny clean, l decided to start with fine paste.

Maybe your fine paste is too coarse? 

Oldiebut goodie wrote: ↑31 Dec 2024, 16:48 Maybe your fine paste is too coarse? 

Maybe? Or maybe l've no clue what I'm doing.
Surely it cannot be that difficult? Perhaps l'm being over critical?

I've two different makes. Tried both.

The last time I lapped valves in, I 'blued them out' with engineers blue. I think there's a tin of it in the office at work. I'll have a look when I'm back in this week. You can have it if you want.

https://waltersandwalters.co.uk/stuarts ... ue_tin_38g

Possibly you are being too critical!
A friend, many years ago, used to polish all combustion surfaces with jewellers rouge until everything was mirror finish - he needed every last ounce of power as he built drag racing bikes. He did it after every outing.

tobydog wrote: ↑31 Dec 2024, 17:50 The last time I lapped valves in, I 'blued them out' with engineers blue. I think there's a tin of it in the office at work. I'll have a look when I'm back in this week. You can have it if you want.

https://waltersandwalters.co.uk/stuarts ... ue_tin_38g

That is very kind of you. But it doesn't warrant that kind of scrutiny.
I will fluid test head once all four valves are lapped. Surely that tells me the valves and valve seals are good?

Oldiebut goodie wrote: ↑31 Dec 2024, 18:05 Possibly you are being too critical!
A friend, many years ago, used to polish all combustion surfaces with jewellers rouge until everything was mirror finish - he needed every last ounce of power as he built drag racing bikes. He did it after every outing.

I used rouge when working in a jewellery shop in Bromley in 1978. Ideal for removing minor scratches from silver or plate ware.
A local mate of mine, with vast experience rebuilding mini engines, is popping round tomorrow to give me the skinny how to properly do this task.
Stay tuned

maxstu wrote: ↑31 Dec 2024, 18:32

tobydog wrote: ↑31 Dec 2024, 17:50 The last time I lapped valves in, I 'blued them out' with engineers blue. I think there's a tin of it in the office at work. I'll have a look when I'm back in this week. You can have it if you want.

https://waltersandwalters.co.uk/stuarts ... ue_tin_38g

That is very kind of you. But it doesn't warrant that kind of scrutiny.
I will fluid test head once all four valves are lapped. Surely that tells me the valves and valve seals are good?

It will show if the seat is round or oval and concentric with the valve. I used to use it as an apprentice mould toolmaker for checking shut offs many years ago.

What are the valve guides like for clearance?
 

Good guides. Well in spec.
Will chat with Jim tomorrow and ask his opinion.
Happy New Year to all!

Jim mixed a bit of oil in the fine paste then showed me a slow version of lapping in NEW valves.
Oil the stem.
Put spots of paste around valve.
Mark valve with felt tip so you can check it's rotating just over 360 degrees.
Drop valve into guide.
Knock valve down onto seat a couple of times to evenly spread paste.
Five slow forward and back. No downward pressure.
Rotate valve 90 degrees and repeat three more times.
Remove valve and clean off paste.
Check lapping on seat and valve.
Repeat with more paste as necessary for this finish. See top photo.
Thoroughly clean heads and valves to remove excess paste.
Mark up and store away.