Lapping / Valve seat grinding

[strath44]

Have looked at a few threads on this as well as you tube. Can anyone give me some pointers never done it before!!??

I have cleaned all the valves up and tried a small amount of grinding on the first valve but have no idea how long to spend on each one - I'm worried about over lapping / grinding the seats!

After a few secs of grinding the valve (used fine compound only not coarse) went from being shiny to slightly dull (left hand valve in pic / original valve on right) is this how it should look???

How long should this take roughly also 2 seats are very pitted as seen??? cheers

[HondaDustR]

Basicly, grind until you get a smooth even ring all the way around the valve and the seat. Pitted or burned seats are what the coarse paste is for. Get rid of most of the defects and then finish off with the fine. The dull grey color is normal. Do not push too hard when lapping. Be very careful not to get any on the valve stem or guide as it will scratch stuff up pretty easily. Those pits *may* be too deep to lap out and may need to be cut at the machine shop.

Check the distances shown here. Distance A can't exceed 14.5mm, and the seat sealing surface widths should stay roughly within +/-0.2mm of 2mm for the intake and 1.7mm for the exhaust.

[dg58004]

you need to make sure that everything stays on a 45 dergee angle or the valve and the seat will not hold pressure correctly. In the one pic. close up that you took of the seat their is a lot of pitting that needs to be ground out. If the pits will not clean up you might have to have a new seat installed. Also you should have a 3 angle valve job on the seats for better flow. Since you have the valves out are you going to top them. Just make sure you get the angles correct or your Porsche will not run correctly.

[WestonP22]

Tip: Use a drop of hot-glue to hold the lapping stick to the valve... The suction cup alone is unreliable and irritating.

[PAUERMAN]

You need your valve seats cut. They are very pitted and need refreshing.

The dull finish on your lapped valve shows you how "wide" the contact patch is on the valve face. This is also referred to as the "reveal" and given that your reveal is the width of the valve face, this is a sign that the seats need to be recut.

Once the seat is cut and you've lapped the valve, the reveal should be a small strip that sits in the middle of the valve face. As the valve seat and valve face wear, the reveal becomes wider to the point of where you are now - needing a valve job.

[bazar01]

If the seats are that pitted, may be better off taking the head to a machine shop and shell out at least $180 to refresh it.
You will have peace of mind that when you put it together, you will have good compression and leak down numbers assuming your cylinders and pistons are still up to spec.

[John_AZ]

strath44.

Listen to bazar01 and many others shaking their heads in disbelief you do not just take the head back to the machine shop and let them finish the work with the skills and tools needed.

GL
John_AZ

[strath44]

John -

first are you prone to exaggeration "shaking their heads in disbelief"

the head is just back from the shop they said the valves would be okay to go back in with some lapping, sometimes chucking money at it continually isn't an option especially when my only nearby option for a machine shop may not actually know there stuff according to what your saying, which is why I put the post up in the first place!!

[John_AZ]

strath44,

You are a gentleman in your evaluation.

Success to your project.

John_AZ

[strath44]

As are you! apologies if that was defensive I'm having a very bad week and its only Monday!

[Rasta Monsta]

Ah, grace and tranquility. Kudos to both.

[ScoobySteve]

Findng out one has to spend more money and time on a project is never fun. I'm about to be doing the head job shortly. I think my Many944s head shipped out today.