Resurface heads EVERY time they're off?
02-29-2012, 10:43 AM
#21
Cylinder pressure is cylinder pressure. What is used to seal in whatever application is addressed accordingly. So you could compare apples to oranges, when it comes to the type of application, because of the supporting parts can make it an equal playing field. Tuning being equal in each application and all..
02-29-2012, 02:36 PM
#22
I still don't believe in milling a head if I don't have to. If its true an straight I bolt it up and go.
So if you go to the track and blow your engine up 5 times in a season and the heads have nothing wrong with them you would mill your heads 5 times? That's absurd.
You start playing into PTV and pushrod length issues if you keep doing that. Why not save that for when they really need to be milled?
I can't tell you how many times I have over heated an iron headed SBC chevy and just change the gaskets and roll out. I don't mean 250-275* either. I talking 350+ degrees. I know not to do that with the aluminum stuff but I can't see surfacing a head if it doesn't need it.
So if you go to the track and blow your engine up 5 times in a season and the heads have nothing wrong with them you would mill your heads 5 times? That's absurd.
You start playing into PTV and pushrod length issues if you keep doing that. Why not save that for when they really need to be milled?I can't tell you how many times I have over heated an iron headed SBC chevy and just change the gaskets and roll out. I don't mean 250-275* either. I talking 350+ degrees. I know not to do that with the aluminum stuff but I can't see surfacing a head if it doesn't need it.
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LS420 (03-08-2023)
02-29-2012, 08:51 PM
#23
I work for a GM dealer, we pull heads off on a regular basis for piston ring problems and what not. We never send the heads off to be machined. Check for warpage and go with it. There are specs for allowable warpage in most service manuals. Alot of GM stuff is not supposed to be machined and if it does GM says to get a new one.
I have seen guys machine heads on regular daily driver stuff and then they cant figure out why it keeps throwing knock sensor codes. B/C they raised the CR and now it knocks all the time on pump gas.
I have seen guys machine heads on regular daily driver stuff and then they cant figure out why it keeps throwing knock sensor codes. B/C they raised the CR and now it knocks all the time on pump gas.
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LS420 (03-08-2023)
03-01-2012, 10:20 AM
#24
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This thread is dumb for so many reasons. I have never seen so many apples to oranges comparisons on one page in my life. There is no one right answer for the OPs question. I've always resurfaced, but that does not mean I think it was mandatory every time. I also don't work on 5xx c.i. race engines or school buses or B52s or Sherman tanks.
If it helps, the engine is an L76 with standard headgaskets, factory TQ to yield bolts, and has never been apart. I've been throwing 9psi at it, without a single hiccup. Since reading through here, I've decided to pick up a straight-edge and check for flat when the heads come off. If there's a hint of an issue with them, they'll be sent to a machine shop.
I'm not spinning this engine to the moon. It'll retain a 6500RPM rev-limit, and wont see above 12/13psi from the twins. I have her on an E85 diet as well.
03-02-2012, 08:57 AM
#25
I cant tell you how many times I have rebuilt a circle track engine's heads that see's a constant 220-240 degree temps for hours on end and never milled the heads on each rebuild. Glass bead the chambers and flat sand the deck. But check and make sure it is flat first.
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LS420 (03-08-2023)
03-06-2012, 10:27 PM
#26
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If an aluminum head is used for any length of time with a standard composite gasket with a wire fire ring, it will indent and cause brinelling from the heat cycling - generally we resurface aluminum heads that use a composite gasket every time they are removed. With an MLS gasket this is not necessary, inspect the head for warp beyond .002", and check the surface carefully for any scaring or scratches in the sealing areas as the viton layer on the MLS gasket cannot compensate for damage like a composite can. If everything checks out ok then you can reuse the head without surfacing.
Again - MLS gasket, usually ok to skip surfacing if head is flat and not scratched.
Composite gasket, usually requires resurfacing if there is a decent amount of run time....race engines can usually get by because they don't heat cycle as much as a daily driver.
Again - MLS gasket, usually ok to skip surfacing if head is flat and not scratched.
Composite gasket, usually requires resurfacing if there is a decent amount of run time....race engines can usually get by because they don't heat cycle as much as a daily driver.
03-09-2012, 12:00 AM
#27
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Here's a twist.....how does head REMOVAL effect the need for resurfacing? Say one takes each bolt out completely one at a time and another backs each one off slowly allowing the head to rise evenly.......I'm curious.
03-10-2012, 08:45 PM
#29
If an aluminum head is used for any length of time with a standard composite gasket with a wire fire ring, it will indent and cause brinelling from the heat cycling - generally we resurface aluminum heads that use a composite gasket every time they are removed. With an MLS gasket this is not necessary, inspect the head for warp beyond .002", and check the surface carefully for any scaring or scratches in the sealing areas as the viton layer on the MLS gasket cannot compensate for damage like a composite can. If everything checks out ok then you can reuse the head without surfacing.
Again - MLS gasket, usually ok to skip surfacing if head is flat and not scratched.
Composite gasket, usually requires resurfacing if there is a decent amount of run time....race engines can usually get by because they don't heat cycle as much as a daily driver.
Again - MLS gasket, usually ok to skip surfacing if head is flat and not scratched.
Composite gasket, usually requires resurfacing if there is a decent amount of run time....race engines can usually get by because they don't heat cycle as much as a daily driver.
I know its been awhile but I kinda remember GM tolerance being .006
03-10-2012, 09:44 PM
#30
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All manufacturers have different specs for their different heads, one might say .002" over a 6" test area, another might say .006" over the length of the head, or as little as .002" over the length of the head. Some heads are less likely to pull back down completely flat when you torque them due to structural head rigidity and size/placement of the fasteners. If a head has more than .002" of warp then it was overheated at some point, but not terribly, this still means though that there can be low and high spots across the head which can cause an issue, and IMO if the head is off already it's better to error on the safe side and skim a couple off the deck to make it perfect.
03-11-2012, 07:33 AM
#32
I can't believe how many ridiculous replies there are here in the midst of a few guys trying to give good information.
You should INSPECT your heads any time they're off...PERIOD. IF the heads are significantly warped, you most likely should NOT fix them by resurfacing. When you do that...yeah sure you get a flat deck surface...and you also get chambers that are 4 different volumes (per head, possibly 8 different volumes per engine)...if they're significantly warped...scrap them (practice porting on them, cut them up to see how they work...something) and replace them.
If you find very minor scratches on an otherwise flat head...weigh your options and take into consideration what the engine is going to do...if it's a mild street setup, and it isn't going to be tuned to the verge of spark knock...consider a minimal amount of material removal JUST to fix the surface...remember, the head still needs to be relatively flat so that all of the chambers are still the same size when you're done.
If the surface of the head is ok (flat) and the head is flat...clean it with some MEK and a SOFT scuff pad (very very gently)...follow that with some brake cleaner or carb cleaner and a soft rag (I prefer to use a cheap microfiber as they don't leave lint like shop rags might), then assemble the engine.
If you're building a turbo/blower setup and using GM castings...resurfacing the heads is going to eventually result in a head that can't hold down on a gasket. I skimmed my 317's for my turbo car VERY VERY slightly (we removed 0.003" from them) because I wanted a better surface finish than stock for the cometic gaskets...if they need to come off...for some reason (lifters need attention would be my only reason), they'll get cleaned the way I described above (maybe without the scuff pad) and checked for flatness...and put back on.
ALWAYS check...never blindly remove material from parts without understanding the consequences. A straight edge is cheap, a flashlight is also cheap, and a feeler gauge set is also cheap...with those 3 items, ANYONE can check their heads for flatness and scratches in the sealing surface.
You should INSPECT your heads any time they're off...PERIOD. IF the heads are significantly warped, you most likely should NOT fix them by resurfacing. When you do that...yeah sure you get a flat deck surface...and you also get chambers that are 4 different volumes (per head, possibly 8 different volumes per engine)...if they're significantly warped...scrap them (practice porting on them, cut them up to see how they work...something) and replace them.
If you find very minor scratches on an otherwise flat head...weigh your options and take into consideration what the engine is going to do...if it's a mild street setup, and it isn't going to be tuned to the verge of spark knock...consider a minimal amount of material removal JUST to fix the surface...remember, the head still needs to be relatively flat so that all of the chambers are still the same size when you're done.
If the surface of the head is ok (flat) and the head is flat...clean it with some MEK and a SOFT scuff pad (very very gently)...follow that with some brake cleaner or carb cleaner and a soft rag (I prefer to use a cheap microfiber as they don't leave lint like shop rags might), then assemble the engine.
If you're building a turbo/blower setup and using GM castings...resurfacing the heads is going to eventually result in a head that can't hold down on a gasket. I skimmed my 317's for my turbo car VERY VERY slightly (we removed 0.003" from them) because I wanted a better surface finish than stock for the cometic gaskets...if they need to come off...for some reason (lifters need attention would be my only reason), they'll get cleaned the way I described above (maybe without the scuff pad) and checked for flatness...and put back on.
ALWAYS check...never blindly remove material from parts without understanding the consequences. A straight edge is cheap, a flashlight is also cheap, and a feeler gauge set is also cheap...with those 3 items, ANYONE can check their heads for flatness and scratches in the sealing surface.
03-13-2012, 08:02 PM
#33
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In regards to the previous post about where the specs come from, this is the engine specification software that is supplied by the AERA. Some examples of the variance in specs even between the same engine family.
03-14-2012, 12:56 PM
#34
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That's the same software we use at our shop. When I say surface them each time, I'm not talking about .015 a whack, just .003-.005 to clean them up. That won't even change the combustion chambers by 1cc, the engine won't be able to tell the difference and you get the peace of mind to know your head surface is perfect for those new gaskets.
03-14-2012, 03:40 PM
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That's the same software we use at our shop. When I say surface them each time, I'm not talking about .015 a whack, just .003-.005 to clean them up. That won't even change the combustion chambers by 1cc, the engine won't be able to tell the difference and you get the peace of mind to know your head surface is perfect for those new gaskets.
This is what i was always told looking for more input from the engine builders?
06-13-2019, 05:52 AM
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Is a few scratches ok? I checked with a Starrett No 308 straight edge and a 0.0015 feeler gauge and nothing passes. I did however scratch a couple of spots. Very light scratches.
What should i do?
What should i do?
06-13-2019, 11:45 AM
#40
I have aluminum heads, ran my engine to 260F on two occasions (obviously not on purpose).
Head gaskets never blew, and looked healthy when disassembling the engine for reasons unrelated.
I will not be re-surfacing my heads. The hilarious part, is that some people would lose their minds over this, and call me crazy.
I think people think way too much in to this.
Now... deep scratches that you can feel with your finger-nail, or dig your finger nail in to? Definitely resurface.
Head gaskets never blew, and looked healthy when disassembling the engine for reasons unrelated.
I will not be re-surfacing my heads. The hilarious part, is that some people would lose their minds over this, and call me crazy.
I think people think way too much in to this.
Now... deep scratches that you can feel with your finger-nail, or dig your finger nail in to? Definitely resurface.