Post Valve Job Cylinder Head failing Leak Down test

[dalmatiangirl61]

Just to verify: Valve Lash == Valve Clearance?

I ran the leak down test without the camshaft installed so there should be nothing applying pressure to the valves.

Edit: I didn't actually answer your question, this WRX has the shimless buckets to adjust valve lash.

Yes, valve lash = valve clearance, same thing. Do leak test with cam out, install cam, repeat leak test, if the valves leak with cam installed, you found the problem.

Slowmotion or Turbowerks, explain shimless buckets, how are they adjusted?

 

[PackardV8]

I've done countless valve jobs on Subaru's and never lapped a valve in. What's important is a straight guide so that the pilot (dead or live and preferably carbide) locates on the same centerline as the valve. This is where most shops get it wrong, which leads to misalignment of the valve face and seat. However, if the valve is ground at 44.5 degrees and the seat is 45, it'll show some leakage until it's run in. I had a customer do this exact thing, all worried because it showed 20% leakage when bolted on. I told him to run it, he did, re-tested and got 4%.

Agree. Those who advocate hand lapping of valves are stuck in the Model T-100-years-ago tech. I haven't seen a pro machine shop hand lap valves in this century.

Every head is vacuum tested on the bench. And yes, if one port shows leakage, the first fix is a whack on the tip of the valve stem with a brass hammer. Most times, this reseats the valve and the leak is gone.

FWIW, Subarus most all fail the head gaskets and/or valves between 80,000 - 100,000 miles. The local repair shops here can get one in first thing in the morning, pull both heads and bring them to our shop. If the valves look good, we mount them on the surfacer, valves still in place, mill flat, wash and out the door in an hour. The repair shop reinstalls the heads and the customer drives it home that night for about $1800.

jack vines

 

[EmGo]

However, if the valve is ground at 44.5 degrees and the seat is 45, it'll show some leakage until it's run in.

You guys don't do three-angle valve jobs ? Lazy bastards

 

[moonlight machine]

Yes, valve lash = valve clearance, same thing. Do leak test with cam out, install cam, repeat leak test, if the valves leak with cam installed, you found the problem.

Slowmotion or Turbowerks, explain shimless buckets, how are they adjusted?

Remove the valve and grind the stem. Old Aston Martins are that way also. Goodson offers a trick little tool that holds the bucket and grinds the valve pad inside the bucket. Never used one.

 

[UptownSport]

What would it matter?

He's saying it's leaking without cams installed.

So torquing the head is warping the seats? LoL

I toured the Soobie factory and they had lines of men lapping the valves of assembled engines.

Marvelous.

 

[1953chevB]

Agree. Those who advocate hand lapping of valves are stuck in the Model T-100-years-ago tech. I haven't seen a pro machine shop hand lap valves in this century.

Every head is vacuum tested on the bench. And yes, if one port shows leakage, the first fix is a whack on the tip of the valve stem with a brass hammer. Most times, this reseats the valve and the leak is gone.

FWIW, Subarus most all fail the head gaskets and/or valves between 80,000 - 100,000 miles. The local repair shops here can get one in first thing in the morning, pull both heads and bring them to our shop. If the valves look good, we mount them on the surfacer, valves still in place, mill flat, wash and out the door in an hour. The repair shop reinstalls the heads and the customer drives it home that night for about $1800.

jack vines

we do it because we can , generations of home mechanics, if a customer ask it for do you comply.
seriously I don't trust mechanic shops to work on my hot rod

 

[1953chevB]

What would it matter?

He's saying it's leaking without cams installed.

So torquing the head is warping the seats? LoL

I toured the Soobie factory and they had lines of men lapping the valves of assembled engines.

Marvelous.

so what is the exact error of the torque causing distortion at the valve porting. SWAG

 

[slowmotion]

What would it matter?

He's saying it's leaking without cams installed.

So torquing the head is warping the seats? LoL

I toured the Soobie factory and they had lines of men lapping the valves of assembled engines.

Marvelous.

I have done countless head prep jobs on brand new out-of-the-box Subaru heads as well as used ones, not one had a lapped valve. Subaru, as well as many other brands, have gone to different thickness buckets, you have to change the bucket to get the correct lash.

 

[1953chevB]

lets put this reticule statement about lapping or not to lap

How To Lap Valves

 

[moonlight machine]

lets put this reticule statement about lapping or not to lap

How To Lap Valves

I have an apparatus that looks like a hand crank drill. on closer inspection you see that it has bevel gears on both sides of the bevel connected to the crank handle. The side gear on the crank handle only has teeth half way around, so as it turns it drives only one of the small bevels at a time. this turns the shaft clockwise then anticlockwise as you turn the crank handle. When I got it it had a little plate on the end of the shaft with 2 pins a side on different center distances. This was to turn the valves with the little holes that used to be in valves back in the day. I used to use it with suction cups. It worked fine if you used a bit of finesse, kept the valve head clean and dry and just generally were not being a rock ape.

 

[Turbowerks]

Yes, valve lash = valve clearance, same thing. Do leak test with cam out, install cam, repeat leak test, if the valves leak with cam installed, you found the problem.

Slowmotion or Turbowerks, explain shimless buckets, how are they adjusted?

Shimless briggs and stratton. Adjust installed valve height to set clearance.


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[ratbldr427]

You can beat this subject to death but it is really a simple process.No seat work until guides are checked and repaired if necessary.If your seat cutting / grinding equipment is in good shape the valves will seat interference angle or not.
On standard quick work I always ground an interference angle just for quick break in insurance and no lapping.
For performance work I always ground no interference angle and lapped lightly with a fine compound.Some times use bluing but the lap line won't rub off and I would be very close to where I wanted before lapping,just a couple of turns is necessary.The purpose was to find exactly where the seat was and move it up or down as necessary.I used felt tip pens and marked the seat at three places in progress to locate the seat width and height.Then back cut the valves to get the width a little wider than the seat(the lap line helps here).
Seat cutters are made with the top and bottom angles and correct width.Depending on how bad the seats are they are quick.
Funny when I first heard about 3 angle valve jobs as something new I thought that is how valve jobs have always been done?My instructors in HS were retired mechanics from the thirties - fifties when a lot of mechanics had to be somewhat of a machinist.They could scrape crank bearings and do engine rebuild machine work.

 

[markz528]

You guys don't do three-angle valve jobs ? Lazy bastards

Why on earth would you do 3 angle? That's the dark ages! 5 angle all the way!

 

[Street]

At one stage you could get a round profile with a seat on it, didn't go into the flow characteristics of it if it was worthwhile, so i guess that beats the 5 angle job.

Just to derail the thread even more, say a 4 inch bore and 4 inch piston usually you run 0.002 inch clearance what would the bore size be pre hone ? ie also what is a good rule of thumb for change of size due to honing. bore to x , hone to y where y is piston diameter plus clearance.
i have only done heads in the past when i was working in the game, filling in a few blank areas.

 

[Limy Sami]

Reading all this I'm almost at a complete loss how I managed to repair and rebuild engines, get them running and lasting.

 

[Servicar rider]

Glad some of you guys won't be working on my engines! Some really goofy theories here? Really? lapping valves on assembled engines? Love to see a video of that? Beating on valves with a hammer? Hell no! 5 angle valve jobs on a street car? What a waste of time and doesn't answer the question of excessive leakdown? Grinding seats with head on block? Video time again? Love to see how thats done? I always lap valves to verify seat width and sealing? I don't care about 21st century theories, I go with what's worked for 100 years?

As far as the question about how much material to leave for finish honing a freshly bored cylinder? I always leave about .001. A boring bar will leave miniature threads as it cuts. These threads are about .0005 to .00075 deep. Your hone will "sing" on these threads. When the hone quits singing you give it a few more strokes and check your size and you will be right where you want to be! Nice straight bore on size, no extra work!

 

[Limy Sami]

Amen brother servicar

 

[slowmotion]

"Just to derail the thread even more, say a 4 inch bore and 4 inch piston usually you run 0.002 inch clearance what would the bore size be pre hone ? ie also what is a good rule of thumb for change of size due to honing. bore to x , hone to y where y is piston diameter plus clearance."

Shops with modern honing machines leave typically .004"-.005", I favor .005" on blocks that are prone to serious distortion when deck plates are installed. But you can leave less if the bore finish is smooth enough, as evidenced by servicar's experience. Although when I do Harley's, I still leave at least .004" as I use plates on them, pans and shovels included. The distortion on an iron Harley is usually only .001"-.0015" but rounder is gooder.

 

[1953chevB]

For clearances I go with the OEM specifications. And I use bore gage to inspect the cylinders.

I forgot mention to the OP if he did the leak down with cylinder's at top dead center , and run the test more than once.

I think this pandemic is making people stir crazy. And irrational.

 

[EmGo]

Lazy bastards ! Plateau hone !