steven89 said:
um composite or not when doing a hg there should ALWAYS be machine work involved...at the VERY least a resurfacing of the head even if its a thin slice coming off. theres just no excuse for that.
Anonymous HG Poll
- Thread starter dugums
- Start date
um composite or not when doing a hg there should ALWAYS be machine work involved...at the VERY least a resurfacing of the head even if its a thin slice coming off. theres just no excuse for that.
Idealsupra said:
unless the head and block come back as straight, which I highly doubt with a higher mileage, used engine, even if it's never had a BHG and you are just upgrading to ARP hardware...
starscream5000 said:
exactly i would be amazed to see an aluminum head of the age and mileage 98% of these 7ms are at not be off by at least a bit by now....
also we BOTH know the people who didnt do machine work are almost guranteed to not have even checked for straightness lol.
I have been running 14psi with my setup going on two years is in Novemeber.
It say machine work ..... i used the grey block that is kinda sandy/chalky feeling and rubbed her down. I dont consider that to be machine work but i think its just fine for a good head and block with the stock h/g
It say machine work ..... i used the grey block that is kinda sandy/chalky feeling and rubbed her down. I dont consider that to be machine work but i think its just fine for a good head and block with the stock h/g
dugums said:
I would have to choose "none of the above"
The only option for me is a metal headgasket with the head and deck machined. I think anything else is wasting your time and money. :dunno:
Stock hg has a better chance of sealing without surfacing the deck.
bigaaron said:
Haha, somehow I knew that's what you were going to say.
I do appreciate the input on the stock HG, though. I may have the opportunity to machine the block thanks to you guys being in Cali - my turbo might just be gone long enough for me to make some time :naughty:
bigaaron said:
There's no question that's the concensus here, and reason backs up what you say about the composite HG, but look at the results so far. This is nowhere near a scientific study, but wow. I would've thought there would have been some consequences showing up for lack of machine work. Is anybody else surprised?
Shytheed Dumas said:
I would definitely like to see more results in the poll.
Yeah, the point wasn't to argue with the "right" way as-directed by the MHG manufacturers, rather just to see what people were actually doing. Maybe all the people who blew MHG's got out of the Supra game altogether...:cry: :evil2:
Or are embarassed. I highly doubt that only 6 people on this forum have blown headgaskets...regardless of prep. I think we have more current BHG threads than that going on right now. lol
Sawbladz said:
Alright everybody: This poll is anonymous and only helpful if we have a bunch of truthful responses.
Hypothetical scenario:
You do a HG, it blows. You do another one, it is fine.
They were both MHG with head only machined.
PLEASE report the blown one as it is more useful data.
i bought my car with a bhg but the motor had been recently rebuild tobad for him he used a cheap gaket set and reused stock headbolts and torqued to factory specsand was running 12psi. All that added u to me buying a supra with 130k and a rebuilt 7m for 700$ so all i did was check the block had the head resurfaced used a titan mhg and arp head bolts. Worked fine for me
Problem is 85% of the shops will clamp down the head, and either move it and reclamp to do entire face, or not have it clamped correctly, thus when it gets machined, it essetially takes the HIGH spots, which can be bad.
If you took a brick, and somehow twisted it, then measured the amount it was "warped" and then took a grinder and made one side flat with the ground the other side is still warped. Many times you get a harmonic "knock" in and around 2800-3200 RPM, if the machining has been done incorrectly. Although nice and tight when it is first up and running after the milling, what happens is the CAMS are straight, and want to remain that way because they are balanced and turning, but when the head was milled and the high spots taken off the bottom.... if it was not torqued down to the mill table properly the TOP side of the head is now out of alignment. This pulls the CAM JOURNALS off centerline when the head is torqued down, and if this happens a MHG compounds the issue because of the fact that there is less "give" in it, over the composite. End result your NEW motor with fresh pistons and valve seals, and all your new parts sounds nice and tight (because it is) for about 2000-3000 miles. At which point the cams ( that have actually been RUBBING the journals that are out of alignment) wear the journals enough t the point there is much more slackfor them to "walk" around. You get into the harmonic areas of the engine, and they do a little jogging and shaking, making noises. "It sounds like a rod knock, but seems to be in the head...."
Never ever take a head to a shop and have tell them "Just clean the block surface up ..." what they are going to do is take it over to the surface grinder and lay it on the nice flat table hold it and turn it on until the surface has a nice uniform finish. Now they have taken your twisted brick and made one side flat, in an unstressed situation. It will bolt down fine, and torque good, and yes the bottom will be flat, but the top is still in the unstressed "twist".
If anyone has had there head recently done and has it torqued down on the block, no timing belt on, you should be able to EASILY turn the cams, and giving them a quick spin they should have only the assembly lube friction. If they are hard to turn and you have torqued the cam caps, and the head to proper specs. I would take it back to whatever shop did the machine work and ask them what they are going to do about your head surface. If it is ran like that it is very hard to find oversized cams......... and you will not know until down the road 1-4 or 6 months depending on how much you drive the car, by then they are certainly going to say it was not thier fault.
Sorry about rambling, just seems to be a common issue I have seen 3-4 times with members that have had machine work done, and I really hate to see dreams ruined by incorrect work.
JoelD
If you took a brick, and somehow twisted it, then measured the amount it was "warped" and then took a grinder and made one side flat with the ground the other side is still warped. Many times you get a harmonic "knock" in and around 2800-3200 RPM, if the machining has been done incorrectly. Although nice and tight when it is first up and running after the milling, what happens is the CAMS are straight, and want to remain that way because they are balanced and turning, but when the head was milled and the high spots taken off the bottom.... if it was not torqued down to the mill table properly the TOP side of the head is now out of alignment. This pulls the CAM JOURNALS off centerline when the head is torqued down, and if this happens a MHG compounds the issue because of the fact that there is less "give" in it, over the composite. End result your NEW motor with fresh pistons and valve seals, and all your new parts sounds nice and tight (because it is) for about 2000-3000 miles. At which point the cams ( that have actually been RUBBING the journals that are out of alignment) wear the journals enough t the point there is much more slackfor them to "walk" around. You get into the harmonic areas of the engine, and they do a little jogging and shaking, making noises. "It sounds like a rod knock, but seems to be in the head...."
Never ever take a head to a shop and have tell them "Just clean the block surface up ..." what they are going to do is take it over to the surface grinder and lay it on the nice flat table hold it and turn it on until the surface has a nice uniform finish. Now they have taken your twisted brick and made one side flat, in an unstressed situation. It will bolt down fine, and torque good, and yes the bottom will be flat, but the top is still in the unstressed "twist".
If anyone has had there head recently done and has it torqued down on the block, no timing belt on, you should be able to EASILY turn the cams, and giving them a quick spin they should have only the assembly lube friction. If they are hard to turn and you have torqued the cam caps, and the head to proper specs. I would take it back to whatever shop did the machine work and ask them what they are going to do about your head surface. If it is ran like that it is very hard to find oversized cams......... and you will not know until down the road 1-4 or 6 months depending on how much you drive the car, by then they are certainly going to say it was not thier fault.
Sorry about rambling, just seems to be a common issue I have seen 3-4 times with members that have had machine work done, and I really hate to see dreams ruined by incorrect work.
JoelD
Shytheed Dumas said:
There's a new bhg thread literally every other day. There's never a shortage of people who do things the cheap/easy/wrong way.
Shytheed Dumas said:
Aha! (Hi Kurt)
In my previous point I stated issues with the machine work. Chances are Toyota has done a very good job originally on the head hell they made it right. The head on a 7m is friggen LONG.... thus warpes easily, and gets twisted. 90% of them in a not torqued state are probably close to if not out of spec. The number on the "no-machining" really does not surprize me because of the fact that, from the factory the thing is straight, and as long as you pull it back down FLAT it is going to be right. Many Supra enthusiasts know that the factory spec is low for head torque, and most go to ARP's and higher torque. If Toyota put the head on at 58 Ft. Lbs. originally, and you pull it off clean the old gasket from the block and head, then put it back on with say ARP's and torque to 70+ Ft. Lbs. chances are the warp that it developed at 58 Ft. Lbs. is gone. Any machining and you take a chance of it being thrown off and there the issues start. I may be eggagerating with the %'s on shops, but that is just from what I've seen locally here.
suprasman01 said:
LOL OMG, let me get this straight...
Soooooooo you are saying that Toyota made it flat, so you are actually making it worse by machining it? And since it is long, it must be flat, and there is no way the deck could have a low spot.
My subscription to this thread is hereby deleted. :biglaugh:
But before I go, here is something for you guys who don't do any surfacing.
You will be seeing this soon......in person.
You will be seeing this soon......in person.
bigaaron said:
Wow, that is an abrupt response...... Not trying to piss anyone off, just sharing experience. Sorry if I was misunderstood.
Not saying machine work is not necessary, or that machine work is bad. Just saying that BAD machine work is bad. Also wasn't saying that because it is long it is flat. Just saying because it is long there is a lot of it to work with to machine correctly. If you torque it down with 14 head bolts, to make sure it is flat on the block, how does your machine shop get the head UPSIDE DOWN, on a mill table and insure you that the whole thing is in the same "PULL" that it is going to be on when it is finished and torqued to your block.
In response to the low spot, it may have one while it is warped and unstressed BUT I will bet that TOYOTA didn't ship it with a low spot, and that the head is the same thickness from the block surface to the bottom of the cam journal ANYwhere you measure on an untouched unmilled tourqed down head. Yes it may be warped but it didn't loose material from the block to head surface while driving the thing down the road.....
Not trying to be a know it all, just trying to save folks from putting something on thier car that will be money out the window. Just putting a check out there that people can do to insure they got a good job.
Torque the head down and install the cams, then before you put the belt on, spin the cams..... easy to do, should JUST feel the valve spring tension and it should be SMOOTH.
JoelD
I can't hear you, my subscription was deleted.
I'm just messing around, I'm not mad. :icon_razz
The deck and head do weird things when they get overheated. Of course they were flat at some point, but after 15+ years and being overheated a few times, there is not only surface erosion, but the deck can develop low spots, and the head can warp. Just because you tighten it down above Toyota specs doesn't mean it will put even pressure across the entire head gasket.
The stock headgasket must be made of compressed poop, because it doesn't work for shit! :biglaugh:
I'm just messing around, I'm not mad. :icon_razz
The deck and head do weird things when they get overheated. Of course they were flat at some point, but after 15+ years and being overheated a few times, there is not only surface erosion, but the deck can develop low spots, and the head can warp. Just because you tighten it down above Toyota specs doesn't mean it will put even pressure across the entire head gasket.
The stock headgasket must be made of compressed poop, because it doesn't work for shit! :biglaugh:
bigaaron said:
ROFL, True on all points, pitting from corrosion, and warping from heat cycles coupled with the low torque and poop gasket. LOL. BTW nice site, checked it out, not a mkIII guy myself but do have a 7mgte in my mkII, and found this thread interesting. I figured I'd post up on what I have seen in the past. Mob took his head last year I think to a shop and was going on the cheap, told them to "clean up the surface" and about 1200 miles later got a harmonic knock. Upon pulling the valve covers we noticed that the oil sitting in teh caps of the cam bolts looked like a strippers cleavage:aigo: , little sparkles everywhere. The cams had been eating into the journals, from where the surface was just "cleaned up" by a local shop.