Block and head just machined and am not sure if MLS will seal

EagleTalonTim · 05-12-2012, 09:14 AM

Hello all once again! I am in the middle of a full rebuild and decided to try to go with an MLS head gasket again. The last one did not seal since I did not have the block machined. I called many companies around my area to ensure the one I chose used a mill machine and not a sander. Only one is in my area

I spent $300 having the block dipped, head and block resurfaced, install my supertech valves and springs, and install new valve stem seals. The owner ensured me he had been doing this kind of work for over 30 years, but I am not sure if it was done right. On both the block and head surface, I can feel and see mill lines. Like little ribs all the way down the surfaces. They are very small and I am sure an OEM gasket would seal, but I am wanting to go MLS for higher pressures and my 500 HP goal. Are the small ribs going to be a problem? If needed, I can try to post a picture.

kchaazz · 05-12-2012, 09:21 AM

A picture would be most helpful. What RA were the surfaces machined to? Ask, then look at what surface RA is required for the gasket to seal properly, and youll have your answer, but post pics anyway so we can see.

2slow4now · 05-12-2012, 09:34 AM

The smoother the better with a MLS. Mirror finish would be ideal IMO. I think the spec required by cometic was about 50 ra.

EagleTalonTim · 05-12-2012, 09:48 AM

Here are some pics that I could get. What does RA stand for? I just called the machine shop and he said he never used RA on his mill machine. He also stated he has used the same setting for hundreds of other race engine builds and never had an issue.

DSMReviver · 05-12-2012, 09:57 AM

RA stands for "Roughness Average". If your head is not within 40RA's(i believe, but check with your head gasket manufacture) it will never seal the head and you will push coolant. How bad coolant will you push? It depends on how rough your surface is.

This is the same problem (pushing coolant) i am having right now. I've used MLS head gasket without surfacing the head and the block. Now the head needs to come off again and either i machine both the surfaces or use OEM composite gasket thats the only way its gonna cure it. Right now its not that bad but i know running the car like this is just a matter of time before the head gasket blows.

you probably need to put your head and your block under a laser to see what your surface finishes are.

1983gsp · 05-12-2012, 09:58 AM

He should have slowed the table speed down and increased the cutter speed. Just my two ¢

EagleTalonTim · 05-12-2012, 10:01 AM

He just called me back and said the last time his machine was checked, it was within 24 to 30 RA. He is having someone come in and check it Monday and will call me back...i hope. Sounds like he is upset with me for questioning his work. I have to question it since I am concerned....especially since I have put $3k into this engine so far and have not started building it

1983gsp · 05-12-2012, 10:04 AM

Wrong Surface Finish To seal properly, a head gasket requires a surface finish that is within a recommended range. The specifications vary depending on the type of head gasket. If the surface is too rough, or in some cases too smooth, the gasket may not seal properly and leak or fail. One common mistake to avoid here is not looking up the recommended specifications for a particular engine and/or a particular type of head gasket.

As a rule, the recommended surface finish for a traditional composition style soft-face head gasket in an engine with cast iron heads and block is 60 to 120 microinches Ra (roughness average). But the recommended surface finish for the same type of head gasket in an engine with an aluminum head on a cast iron block is smoother, typically 20 to 50 microinches Ra. On late model engines with multi-layer steel (MLS) head gaskets, the OEM surface finish recommendations tend to be even smoother, say 20 to 30 microinches Ra or even 7 to 15 Ra. But the aftermarket also sells MLS gaskets with special coatings for many of these same applications that can handle surface finishes in the 50 to 60 microinch Ra range. So you have to know your gaskets and the surface finish recommendations for them by the gasket manufacturer, or the OEM if you are using a factory-style replacement head gasket.

Don’t assume close enough is good enough. Eye-balling the surface finish will tell you if the surface is really smooth (a mirror-like finish), really rough (like sandpaper) or somewhere in between, but it won’t tell you if you are in the recommended range. Dragging your fingernail across the surface isn’t much better, either, because a 30 Ra finish feels almost identical to a 50 Ra finish. And the smoother the finish gets, the more difficult it is to see or feel much difference.

The only way to accurately determine if the surface finish is within the correct range is to check it with a profilometer. This is an expensive electronic instrument that drags a diamond-tipped stylus across the surface to calculate its profile characteristics. The profilometer can then display various values for the surface including roughness average (Ra), average peak height (Rpk), average valley depth (Rvk), and even waviness. These numbers may not be needed for an economy Chevy 350 rebuild, but they can be critical when building high performance engines or durability engines. The mistake to avoid here is assuming the surface finish is correct when you haven’t actually measured it.

Wrong Feed Rate/Speed The quality and smoothness of the surface finish requires using the correct feed rate and speed for the type of tool bit. This, in turn, will vary depending on the diameter of the cutter head.

To achieve the best possible finish, you should use a higher spindle speed and lower table feed rate with a very shallow cut on the final pass (less than .001").

If you are using a carbide insert to refinish a cast iron head, the spindle rpm required will typically be about 140 rpm for an 11-inch cutter, 120 rpm for a 13-inch cutter or 110 rpm for a 14-inch cutter.

With CBN (cubic boron nitride) or PCD (polycrystaline diamond) inserts, the recommended spindle speeds are much higher: 1040 rpm for a 11-inch cutter, 880 rpm for 13-inch cutter, or 720 rpm for a 14-inch cutter. If the head or block being resurfaced is harder, high silicon content alloy, the speeds need to be slowed down a bit: 690 rpm for a 11-inch cutter, 580 rpm for a 13-inch cutter or 540 rpm for a 14-inch cutter.

With a single CBN or PCD insert cutter spinning at 1,000 to 1,500 rpm, the feed rate should probably be less than two inches per minute on the final cut to achieve a surface finish in the low teens.(copy paste from engine builder mag)

DSMReviver · 05-12-2012, 10:10 AM

Quote:

Originally Posted by EagleTalonTim

He just called me back and said the last time his machine was checked, it was within 24 to 30 RA. He is having someone come in and check it Monday and will call me back...i hope. Sounds like he is upset with me for questioning his work. I have to question it since I am concerned....especially since I have put $3k into this engine so far and have not started building it

Hey i give you props for taking the courage to question his work. Everybody needs to do it with their machine shop. Always recheck their work from the top to bottom. You cannot relied on somebody to always do the right thing. People get lazy if they do the same work over and over again.

I failed to recheck my work and the result is time and money wasted.

BogusSVO · 05-12-2012, 10:18 AM

The tool markings on the block look like they were done on some sort of multi-tooth rotory broach.

These should help...
How to Surface a 4G63T Cylinder head for a MLS head gasket

How to deck a 4G63 Cast Iron Block

EagleTalonTim · 05-12-2012, 02:57 PM

from the looks of the picture, would anyone have any doubts that an MLS headgasket will seal? Should I just go with a stock headgasket? I plan on maxing out my Big 16G till it dies and then upgrade to an hx35 or similar. I can only run 93 pump gas so I have to build to what I can get for max power on pump gas.

EDIT : I do plan on using Copper head gasket sealant to help seal as well.

2slow4now · 05-13-2012, 03:30 PM

E.T. Tim with something like a head gasket I wouldn't just wing it. My $.02 is I wouldn't trust a mls on it.

I'm betting your from a smaller town like me. The local performance machine shop does almost exclusively V8 stuff and 99% of the customers throw some 202 heads on with a standard gasket set, maybe forged pistons, some slightly aggressive cams, oh and a 4 barrel. That surface finish he did probably works fine with what he normally does like he says. He sounds like he's probably a pretty good guy to deal with considering he is going to have someone check his machine just because you voiced your opinion/concerns. Good guy or not I would have the RA checked and corrected if need be depending on which gasket you choose and let him see the specs from the manufacturer so to not look like your just a picky azzhole and keep a good machinist as a friend.