Testing valve seal after seat cut

[Guest]

I am cutting the seats on my head, valves have been done at a local machine shop. I install the valves and fill the port with gas.
How much seepage is acceptable?

[mlinder]

None.

What are you using to cut the valve seats?

What was done to the valves?

[gearhead13]

None.

What are you using to cut the valve seats?

What was done to the valves?

I am using a neway cutter for the seats at 45 deg
The valves were refaced at 45
I do not plan to lap them unless I have to.

[mlinder]

Any particular reason you didn't have the shop doing your valves also do your seat?

Just wondering. Seems like often enough, 45 degrees is different in different places...

You have to lap them at least a tiny bit, check to make sure they mate well.

[rapidray]

EVERY head I do, I lap the valves. Street, dirt, race, it doesn't matter. It makes a DIFFERENCE! In my book it is called attention to detail. Ray.

[gearhead13]

The reason I didnt have the shop do the whole head is it would have cost $3-400, this way, I have the tools now and can do my own heads
OK, I will lap them. And when I am talking seepage, I mean just a tiny bit of moisture.

[mlinder]

a tiny bit of seepage at 1 atmosphere is quite a bit different at 160 psi.

That much, eh?

Mike Rieck in Boston (and others) will do an 8 valve serdi job for (far) less than 300 bucks.

You need to find another shop.

[TeamDar]

The factory Suzuki service manual recommends NOT lapping the valves if the seat is cut with a neway type seat cutter. The finished valve seat should have a velvety smooth finish and not a highly polished or shiny finish. This will provide a soft surface for the final seating of the valve which will occur during the first few seconds of engine operation. Dar

[gearhead13]

Ya, the shop here is kinda pricey, although the 3-400 would include 1mm oversize intakes and its just a guesstimate. They charged me $5 per valve to cut them. I had a head done by them some time ago but I cant find the receipt for it.
$300 for 8 valves, but mine is a 16 valve.
The reason I wasn't going to lap them is because I read that it wasnt needed if the valves and seats were cut properly.

[mlinder]

Ah, yes. Mo' dollars, then.

[rapidray]

The factory Suzuki service manual recommends NOT lapping the valves if the seat is cut with a neway type seat cutter. The finished valve seat should have a velvety smooth finish and not a highly polished or shiny finish. This will provide a soft surface for the final seating of the valve which will occur during the first few seconds of engine operation. Dar

I KNOW what the book says, Dar, but those seats are anything but SOFT! I get 100% sealing when I lap them, which means there won't be a "comeback". Ray.

[old_chopper]

Lapping the valves also shows you where the sealing area is on the valve. A lot of production shops don't lap them anymore but all of the performance shops I know still do. It's time consuming but as Ray put it it's attention to detail. I say lap them and make sure every hint of the compound is cleaned up before assembly. It loves to eat rings for lunch!

[Nessism]

If the seats/valves are machined correctly there is no need to lap them. Tens of millions are engines are built each year and very few have lapped valves. That said, on a garage done valve job lapping the valves will show you the seat and valve contact pattern and width, as well as knock off any small burrs that may be lurking on the seats. The Suzuki recommendation against lapping was not consistent across their factory manual set; some manuals said to not lap the valves and others said it's okay. Regardless of the manual, lapping won't hurt anything and has various benefits so you might want to give it a try.

[Graham]

I would lap valves if I was using the old valve guides.