Valve lapping and precup skim?

Joined
Mar 10, 2019
Messages
1,053
Location
melbourne, Oz
Like a virgin, first time valve grind. Manual says a light lap after seat cutting. I have coarse and fine oil based lapping paste. New valves. I am trying to get an even abraded band without any lines. Then I go to smooth it with the fine 360?
There is a guy on youtubby who goes to 1000 grit. But I can't see with heat expansion it would make much difference to the seal. The valves are going to go up and down for millions of times. Do I assume wrong?

Also my precups got skimmed with the head at the head shop. Being from stainless the pre cups look like they grabbed a little differently to the cast iron when decked. It is flush. Has anyone seen precups come out like this after decking before?
I read that some shops deck first, then install pre cups, then deck again.
Hard to take a photo of these details.
1661147160484.png

1661147100228.png

1661147029955.png

1661146749781.png
 
Joined
Oct 15, 2010
Messages
215
Location
Quebec, Canada
I have seen skimmed same time as the head and it worked well. I tough it might help to have the protrude so the shop deck the head first and install the cups after. Adjust the protrusion after.
Both ways remove some material from the pre-cups…(making them weaker?)
Tough that I may adjust the height of the protrusion by removing material from underneath of the cups but then it diminishes the size of the pre chamber.
Hard to make something new with old stuff!
 
Joined
Mar 10, 2019
Messages
1,053
Location
melbourne, Oz
I have seen skimmed same time as the head and it worked well. I tough it might help to have the protrude so the shop deck the head first and install the cups after. Adjust the protrusion after.
Both ways remove some material from the pre-cups…(making them weaker?)
Tough that I may adjust the height of the protrusion by removing material from underneath of the cups but then it diminishes the size of the pre chamber.
Hard to make something new with old stuff!
I think I recall a pro builder here saying that he thought there was plenty material in the precups to skim. Admittedly, I am a bit of a skeptic.
A few folks have had precups fall or fail or both on here. I was real careful getting them in.

The machine shop guy who did the work is not a diesel specialist, but a ford v8 race engine specialist, just down the road. He did not like any protrusion. He does care what job he does. He only takes off as little as necessary.

You are right, hard to make new from old, feels like a punt a bit.

But going through the whole engine rebuild process has been an excellent learning experience for me, regardless. But certainly expensive if you stuff up.

I originally ordered two new heads from alibaba last october. They would have been a good price if they ever arrived..so the thieves never respond to emails now. Nearly after a year, covid or not they could at least respond to emails. Not an endearing feeling to say the least.

Engines Australia use the same chinese casting company..few things are actually made in Oz now. Maybe the new heads shall just turn up one day.

Surprised there is not much on valve lapping on mud, yes I did a search...Merci!
 

stevebradford

In the shop
Joined
Nov 7, 2016
Messages
2,340
Location
Langford. Victoria bc
This was new pre cups machined flat with the head at 7000k it developed an exhaust leak sounding tick pulled the head at 10,000k

The offending pre cup and worn away head gasket ring
1E26B0C1-6054-45B6-A7AE-259FD68CF499.jpeg


The new piston and cylinder insert
5639C738-D322-43E4-9DE6-91947AC41705.jpeg
E346E6EF-36F2-4099-8E1A-4E179C402AB4.jpeg


Pre cup holes were throughly cleaned and pre cups bottomed out before machining. Not sure if the non Toyota head gasket or pre cups being machined flat caused this. The Toyota manual does call for some pre cup protrusion.
 
Joined
Mar 10, 2019
Messages
1,053
Location
melbourne, Oz
As you can see, I have no liners. But I have an ome head gasket. Thinking of using some copper goop too.

Was the precup loose? I wonder if your head was re- torqued a few times? The ome bolts have a defined length for a non machined core or head.
I am using arp bolts to make up for the skim of core and deck, it would be more than.1mm shorter in depth than the ome head bolts.
 

stevebradford

In the shop
Joined
Nov 7, 2016
Messages
2,340
Location
Langford. Victoria bc
Wasn’t my motor but the new pre cups fit snug weren’t loose at all (very loose after), the factory bolts were reused, the threads in the block were cleaned and chased. Head was torqued down then retorqued once after warming up. The head gasket was fine with no loss of compression or losing fluids no symptoms other than tick, the section of head gasket under just the one pre cup disappeared out the exhaust.


This time it got a factory mls head gasket with extra metal under the precup area in there rather than the aftermarket fibre gasket, protruding pre cups and it’s running well.
9EC98B7F-0592-47AD-B93F-E29705558889.jpeg
E3DABE87-A12A-4DC0-94FC-515919079D01.jpeg
 
Joined
Mar 10, 2019
Messages
1,053
Location
melbourne, Oz
I wonder if the length of the ome bolts had an influence? Also re using old ones, they may have stretched.
Not sure when they actually bottom out against the core.

Non ome gasket probably did not help either.
A non ome rocker cover gasket is more like plastic compared to the rubbery ome one for example.

Have you got turbo? Is that a 3b?

Coldtaco has/had some 2h mls gaskets but I really don't feel I need them or at least hoping. Also, I would have to go to a different machine shop too, the local one only has old school equipment, can't get it that smooth.

I certainly plan on re-torquing a few times after heat cycles. Don't want turbo.
 
Joined
Oct 15, 2010
Messages
215
Location
Quebec, Canada
I’m not 100% sure but I think torquing a second time is more a MLS kind of thing.
To much torque and the gasket can be destroyed, even a liner can break at the top…but not your case.

In the case of a 3B head bolts aren’t torque to yield and there is space in the bloc. Watch for défaut and corrosion
 

Users who are viewing this thread

Top Bottom