OEM Headgaskets

91 Supra · 07-17-2007, 01:19 AM

Quote:

Originally Posted by cre

If you want the HKS to seal, don't assume anything is in good enough condition. Those are probably the pickiest MHGs out there. If the head and deck aren't flawless it's going to leak.

If you still want a MHG but want something a bit more forgiving look into the one by Cometic. The head and deck still have to be damn near perfect, but the RA can be a bit coarser.

What if instead of the HKS headgasket I went with an OEM headgasket, torqued it properly and did some re-surfacing to the block due to wear and tear?

cre · 07-17-2007, 01:32 AM

Are you planning on upping the boost anytime soon? The stock HG gets a bad rap. The HG wasn't ever the main problem, nor are the OEM headbolts it was the torque specs.

I would recommend new bolts but the OEM bolts are quite beefy. If you want to go with ARP's for the additional security, go for it. The OEM HG is NOT good for more than stock boost levels, I would trust it to last up to about 10, but anything beyond that and you're begging for trouble. There are a few people who I know of that are running 10psi (and have been for a year or more) on an OEM HG torqued to ~72ft lbs.

Even with an oem HG you need to check the deck for pitting, check the deck with a machinists straight edge, have the head cut a little (the HG's rings usually leave impressions which need to be removed), and then lap both for a very good and smooth surface. You may be able to get away with less, but I wouldn't try it. At any rate at this point, if the deck is flat and you do lap the head and deck well, I would probably go with a cometic HG.

91 Supra · 07-17-2007, 02:46 AM

Quote:

Originally Posted by cre

Are you planning on upping the boost anytime soon? The stock HG gets a bad rap. The HG wasn't ever the main problem, nor are the OEM headbolts it was the torque specs.

I would recommend new bolts but the OEM bolts are quite beefy. If you want to go with ARP's for the additional security, go for it. The OEM HG is NOT good for more than stock boost levels, I would trust it to last up to about 10, but anything beyond that and you're begging for trouble. There are a few people who I know of that are running 10psi (and have been for a year or more) on an OEM HG torqued to ~72ft lbs.

Even with an oem HG you need to check the deck for pitting, check the deck with a machinists straight edge, have the head cut a little (the HG's rings usually leave impressions which need to be removed), and then lap both for a very good and smooth surface. You may be able to get away with less, but I wouldn't try it. At any rate at this point, if the deck is flat and you do lap the head and deck well, I would probably go with a cometic HG.

No, at this time I don't have plans in upping the boost, and I probably wont in the future actually. I want to stay as close to stock boost as I can. Either way you provided me with some great insight as to how I should approach the BHG issue. Just to be on the safe side I'll put on a good HG. I'll check out the cometic HG, stick on some arp bolts and studs, torque to about 75 ft lbs and definitely have the head cut a little like you suggested. Thanks a bunch Cre.

cre · 07-17-2007, 04:00 AM

You should still buy/borrow/rent a precision lapping plate and lap the head and deck with some good diamond paste. Make sure to keep the paste out of the oil and coolant passages and clean it all out of the cylinders.

And when I say you need to use a machinists straight edge to check that the block deck is within TSRM specs, I mean it. The tolerances need to be very tight to use any metal head gasket.

91 Supra · 07-17-2007, 04:22 PM

Quote:

Originally Posted by cre

You should still buy/borrow/rent a precision lapping plate and lap the head and deck with some good diamond paste. Make sure to keep the paste out of the oil and coolant passages and clean it all out of the cylinders.

And when I say you need to use a machinists straight edge to check that the block deck is within TSRM specs, I mean it. The tolerances need to be very tight to use any metal head gasket.

Will do, again thanks a bunch Cre

IHateHacks · 07-17-2007, 08:45 PM

Even on an engine that never blew a head gasket, the factory head gasket will leave "bite" marks in the deck of the block, you must remove those if you want to go metal, and shaving the head and using ARP hardware are a must. I removed most of my bite marks but I wimped out and used a stock gasket.

91 Supra · 07-18-2007, 03:42 AM

Quote:

Originally Posted by IHateHacks

Even on an engine that never blew a head gasket, the factory head gasket will leave "bite" marks in the deck of the block, you must remove those if you want to go metal, and shaving the head and using ARP hardware are a must. I removed most of my bite marks but I wimped out and used a stock gasket.

Very true. Im not quite sure what compelled me to think that the deck of my block would be in good enough condition such that I would only need to mount on a new HG and be done with it, I guess I have much to learn about engine wear and tear. Anyways, I'll definitely keep both yours and cre's information/advice in mind as I begin to tackle on this whole BHG deal. Thanks again

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07-17-2007, 01:32 AM	#2
cre Toyota Racing Development Join Date: Apr 2007 Posts: 5,038	Are you planning on upping the boost anytime soon? The stock HG gets a bad rap. The HG wasn't ever the main problem, nor are the OEM headbolts it was the torque specs. I would recommend new bolts but the OEM bolts are quite beefy. If you want to go with ARP's for the additional security, go for it. The OEM HG is NOT good for more than stock boost levels, I would trust it to last up to about 10, but anything beyond that and you're begging for trouble. There are a few people who I know of that are running 10psi (and have been for a year or more) on an OEM HG torqued to ~72ft lbs. Even with an oem HG you need to check the deck for pitting, check the deck with a machinists straight edge, have the head cut a little (the HG's rings usually leave impressions which need to be removed), and then lap both for a very good and smooth surface. You may be able to get away with less, but I wouldn't try it. At any rate at this point, if the deck is flat and you do lap the head and deck well, I would probably go with a cometic HG.

07-17-2007, 04:00 AM	#4
cre Toyota Racing Development Join Date: Apr 2007 Posts: 5,038	You should still buy/borrow/rent a precision lapping plate and lap the head and deck with some good diamond paste. Make sure to keep the paste out of the oil and coolant passages and clean it all out of the cylinders. And when I say you need to use a machinists straight edge to check that the block deck is within TSRM specs, I mean it. The tolerances need to be very tight to use any metal head gasket.

07-17-2007, 08:45 PM	#6
IHateHacks 20psi boost Join Date: May 2006 Location: New Haven/Hamden Posts: 793	Even on an engine that never blew a head gasket, the factory head gasket will leave "bite" marks in the deck of the block, you must remove those if you want to go metal, and shaving the head and using ARP hardware are a must. I removed most of my bite marks but I wimped out and used a stock gasket.