Head warp tolerance with mls head gaskets?

[Mike T]

I've got .003 between the block and the head at the #3 cylinder and .002 on the #4 cylinder (center cylinders). I've been running stock type gaskets but I'm now considering going with cometics. I know .000 would be ideal but I have had the heads cut a couple of times and the intake is just starting to become misaligned.

I'll do what I've got to do but I would like to know if there is an acceptable tolerance.

Thanks Mike.

 

[Nick Micale]

To me those tolerances are not acceptable for a stock type gasket, and the MLS gasket would be less compliant in my opinion.

A head subjected to a blown head gasket must be within 0.001" before I would replace it.

I always vacuum test the valves for sealing before re-installing even if they look good.

Sounds like even a small cut on the heads at this point would require milling the intake to have an optimum fit for the bolts and port matching.

That is easily determined by test fitting the intake after the heads are bolted down, especially if a MLS gasket is used since you have a choice of their final thickness.

 

[Mike T]

Thank you for the reply Nick. I'll get a vacuum tester to check the valves and drop the heads off for surfacing. I don't have a machinist straight edge so that's the reason for checking them on the block. The numbers were repeatable when the heads were swapped from left to right.

 

[fastblackracing]

I've got .003 between the block and the head at the #3 cylinder and .002 on the #4 cylinder (center cylinders). I've been running stock type gaskets but I'm now considering going with cometics. I know .000 would be ideal but I have had the heads cut a couple of times and the intake is just starting to become misaligned.

I'll do what I've got to do but I would like to know if there is an acceptable tolerance.

Thanks Mike.

What thickness mls gasket are you planning to use?..... The stokers are pretty thick, about .060 IIRC, and the mls are available in different thickness...... You may end up better off or worse off on the alignment depending on your choice........ And Nick is 100% right the heads need to be flat if you want trouble free head sealing...... What compression are you at now? You may want to mill every thing into alignment and run a thinner gasket to end up with a little better compression.

 

[TurboTnZ06]

Meh, I ran 10's at 127 on irons that had been shaved 3 times that I know of without touching the intake at all. I had easily a 3/16 inch offset on my stock intake runner alignment, barely could run the intake bolts on and gobbed a ton of sealent as well... Ran fast enough for me. It's not like its right or wrong, but my new engine (2010 is new to me) has the alignment perfect and could be why I have so much more power than before on less boost.

 

[Mike T]

What thickness mls gasket are you planning to use?..... The stokers are pretty thick, about .060 IIRC, and the mls are available in different thickness...... You may end up better off or worse off on the alignment depending on your choice........ And Nick is 100% right the heads need to be flat if you want trouble free head sealing...... What compression are you at now? You may want to mill every thing into alignment and run a thinner gasket to end up with a little better compression.

I'm not sure what thickness to go with yet.... cometic makes one thick enough to correct the intake alignment but the down side is compression loss. I made a few changes that affected the compression ratio but it should have worked out to a little less than stock . While it's down I'll cc the heads again to be certain of where the CR ended up. I'll probably end up using about a .040 gasket, decking the block, surfacing the heads (third time for them) ,cutting the intake and doing a little more intake port matching.

Meh, I ran 10's at 127 on irons that had been shaved 3 times that I know of without touching the intake at all. I had easily a 3/16 inch offset on my stock intake runner alignment, barely could run the intake bolts on and gobbed a ton of sealent as well... Ran fast enough for me. It's not like its right or wrong, but my new engine (2010 is new to me) has the alignment perfect and could be why I have so much more power than before on less boost.

My intake runners were off by about an 1/8 even after a small cut..... at the time I really didn't want to cut it any more because I thought it would be smart to save material for a future build or different heads. Still on the fence but I'll probably have to cut it this time.

 

[Ttype6]

The best way to get the decks flat is to buy a piece of cold or hot rolled steel and have it ground flat. Buy a roll of auto body sand paper that is sticky on one side. You will need three pieces side by side affixed to the flat ground side of the steel. Using circular motions,you will readily see how flat either or both surfaces are. Even after machining each or one surface,you will want to use the steel and sandpaper to finish the job. You'll be surprised how less than flat it can be after having been machined.

 

[Mike T]

The best way to get the decks flat is to buy a piece of cold or hot rolled steel and have it ground flat. Buy a roll of auto body sand paper that is sticky on one side. You will need three pieces side by side affixed to the flat ground side of the steel. Using circular motions,you will readily see how flat either or both surfaces are. Even after machining each or one surface,you will want to use the steel and sandpaper to finish the job. You'll be surprised how less than flat it can be after having been machined.

I would think using your method that you could cut a couple of thousandths without too much effort but have you ever had a problem keeping the head square?
I like your idea and I don't mind putting in the effort as long as the end result is a straight head.


I'm either going Cometic or RJC on the head gaskets so the deck needed to be very smooth. Since the block was going to the machine shop for a hone anyway I decided to run a large whetstone over the deck just to see would happen. I ran the whetstone across the block from several different angles while keep the stroke and pressure as even as possible. It ended up looking very nice and hopefully it's straight.

I left the block with the machinist today for the cylinder hone and asked him to check the deck surface for me. I told him to deck the block if it's not right.

 

[Ttype6]

I would think using your method that you could cut a couple of thousandths without too much effort but have you ever had a problem keeping the head square?
I like your idea and I don't mind putting in the effort as long as the end result is a straight head.


I'm either going Cometic or RJC on the head gaskets so the deck needed to be very smooth. Since the block was going to the machine shop for a hone anyway I decided to run a large whetstone over the deck just to see would happen. I ran the whetstone across the block from several different angles while keep the stroke and pressure as even as possible. It ended up looking very nice and hopefully it straight.

I left the block with the machinist today for the cylinder hone and asked him to check the deck surface for me. I told him to deck the block if it's not right.

I don't know how flat your stone is,but I run my setup over the deck surface of the block and lay it on a flat surface and run the heads over it to see where I stand. Then I have machining done if it looks to be needed. then I use my setup to check the flatness after the machining. On my current build I found that the highest spots on the block's deck surface,after machining,were the areas where the cutter was in contact with the deck surface for the longest time. The highest areas were the two ends and in between the cylinders. The piece of steel I have is flat and very rigid. It will identify high spots very quickly. I start with 400 grit to see how good or bad I am,then go to 240 if I see that I have a long way to go,then end with 400. I also used it to correct the imperfections in the machining that was done to my pan rail for my girdle setup.

The factory decks are cut with a broach. I would think that running a flat abrasive over the surface would have reveled some very distinct high spots. Is this what you found?

 

[turbodave231]

Mike,

Don't cut your intake manifold. You can fix the alignment problem by milling the intake face on the head. With the Buick V6, the intake face is 90 degrees to the deck. So with that angle it is a 1:1 ratio. Whatever you removed from the deck of the head, remove that same amount from the face of intake surface (head side not manifold). This will fix any misalignment and you don't end up with a customized (hacked) manifold.

I have to agree with everyone else's statements. You need dead flat on the block and heads to use Cometic MLS. You also need a very smooth finish (better than 20 Ra. When using Cometics, I always use Hylomar spray on every layer of the gasket. That subject has been fully explored on other threads.

Good Luck

 

[Mike T]

The factory decks are cut with a broach. I would think that running a flat abrasive over the surface would have reveled some very distinct high spots. Is this what you found?

I did work the deck until all of the factory machine marks were gone but in the process I didn't find any areas that really stood out as high or low. I'm very curious what the machinist will have to say about the deck.

Mike,

Don't cut your intake manifold. You can fix the alignment problem by milling the intake face on the head. With the Buick V6, the intake face is 90 degrees to the deck. So with that angle it is a 1:1 ratio. Whatever you removed from the deck of the head, remove that same amount from the face of intake surface (head side not manifold). This will fix any misalignment and you don't end up with a customized (hacked) manifold.

I have to agree with everyone else's statements. You need dead flat on the block and heads to use Cometic MLS. You also need a very smooth finish (better than 20 Ra. When using Cometics, I always use Hylomar spray on every layer of the gasket. That subject has been fully explored on other threads.

Good Luck

Dave that's good info......I'll have the intake side of the heads cut for sure.

While we're on the subject of heads how's your luck been with bronze guides? My heads have bronze guides that were installed about 10k ago and like a lot of other little things in the engine they seem to have excessive wear. With the valves raised about .500 out of the combustion chamber the dial indicator is showing anywhere from .005 to .010 side movement.

I don't have a ball gauge but I can sort of get a caliper inside of the top of the guide and I'm seeing about .003 to .005 larger than the valve stem.

 

[turbodave231]

Mike,

If you are measuring that much valve rock, you already know you have some wear. Probably best to measure the guides and valve for wear. The valves should have less than .001 taper on the stems and clearances should be less than .003 in the guide. Do your guides have the thin bronze inserts or the whole guide is bronze ? Inserts are quick and easy to replace with the right tools.

 

[Mike T]

They're the thin inserts. The stems seem to measure true with my caliper but I'll mic them to be sure. I thought at first the wear may have been due to valve train geometry because there was about a .060 wide scrub pattern on the tips of the stems from the roller rockers. I would think this would side load the valve and cause wear in one direction but the slop is even in all directions although you can see a wear pattern on the stems that indicates side load.

Also on the exhausts valves some of the seats had a contact patch as small as .030 wide so I'm sure the heat wasn't being dissipated like it should have been.