Head Gasket thickness selection

[Cokedoctor]

Okay. My dad had told me this morning that when my machinist stopped by last week, he did some measurements, and according to him my piston protrusion value is .018 above deck surface. Now, how do i figure how much more Head Gasket I need? By reading the Head Gasket Size Calculator, the stock head gasket thickness is 1.37mm. By converting my .018inch to the metric system, I come up with a protrusion of .457mm. This tells me that in other to rid myself of any protrusion, I would need a HG thickness off 1.83mm. Since they do not make a such size, would it be too much to go ahead and buy a 2.00mm gasket? OR should I round down, and find a 1.75mm gasket? I am thinking I should go with the 2.00mm size just to be safe.

 

[IJ.]

Stock out of the hole is 20 thou, I don't see why it's a consideration in your calculations?

You don't need to be so precise, in the past I've used up to a 3mm MHG with little ill effects other than a little fluffy off boost and possibly increased emisions.

Just add whatever has been removed from the block and head and add that to 1.37mm then round it up/down and you'll be fine.

 

[jklfds]

In my search for information on replacing the head gasket I found the webpage below very interesting and usefull.

http://www.totallytriumph.net/spitfire/skimming_your_head.shtml

It explains why the compression ration is so important.
The effect of different fuels on the acceptable compression ratio
How to measure your engine and calculate the gasket/skimming needed to achieve a particular compression ratio.

The article is directed at normally aspirated engines and does not consider the higher dynamic compression that is possible on a turbo engine under boost.

 

[Daxter85]

so i need to resurface both the head n block in order for me to put on a mhg? I was going to put on 3mm so if i go and do this w/o resurfacing anything the mhg will blow?

 

[nuggets]

Daxter85, IMO to do it right you need to resurface the head and block for a MHG. The MHG's are much more reliable than composite gaskets but are less forgiving when it comes defects in the head and block. I used a Cometic MHG for my rebuild and Cometic recommended that the surface finish be 60RA or better. If you don't resurface your head and block I can't say that you will definitely blow the gasket, but if it were me, I wouldn't chance it.

Something that I haven't seen talked about much in this thread is piston selection. IJ, what are your thoughts? Wouldn't that also affect compression ratios? For example, the stock pistons have a dish volume of 19cc whereas my JE Pistons have a dish volume of 29.5cc. Also if you overbore (typically .020" / .5mm) that may change your compression, no?

 

[IJ.]

Daxter85, IMO to do it right you need to resurface the head and block for a MHG. The MHG's are much more reliable than composite gaskets but are less forgiving when it comes defects in the head and block. I used a Cometic MHG for my rebuild and Cometic recommended that the surface finish be 60RA or better. If you don't resurface your head and block I can't say that you will definitely blow the gasket, but if it were me, I wouldn't chance it.

Something that I haven't seen talked about much in this thread is piston selection. IJ, what are your thoughts? Wouldn't that also affect compression ratios? For example, the stock pistons have a dish volume of 19cc whereas my JE Pistons have a dish volume of 29.5cc. Also if you overbore (typically .020" / .5mm) that may change your compression, no?

Exactly, ANYTHING you change above the piston will have an effect on the final compression ratio, I usually CC the head and piston dish then calculate the actual ratio (been lazy since finding a calculator to do it )

 

[destrux]

Proper head gasket thickness is also important because it affects valve timing. The cam and crank sprockets for the timing belt are designed to be a certain distance away from each other and if you move them closer or farther away it will advance or retard the cam timing. You can correct it with adjustable cam sprockets, but it's better to just do it right.


Also I know some people mentioned that using too thick of a gasket will reduce quench.... for those who don't know what quench is... It's as important to the cooling of your engine as adding coolant to your radiator. Without proper quench your pistons can't cool down very well, and will heat up faster than they can shed heat. This will make your engine detonate during extended high load conditions (WOT highway runs, dyno runs, burnouts, drifting or drag racing... basically anything fun) and most likely blow the headgasket (or the pistons, or cause rod knock, or break a rod).

 

[satx88supra]

When measuring the block (i bought my block and it was decked already) is the main saddle bearing the top of the crank where the crank pulley goes. If so.... i'm to measure the top of crank to the top of the block deck with the crank pulley off...correct?!

 

[firegumby]

Does anyone know where to get a composite hg cause all i'm doing is ct26 to ct26 upgrade.

 

[JohnRardin]

What are the benefits or flaws of using a 3.0mm MHG? My buddy just bought a prebuilt 7m with an HKS 3.0mm head gasket and plans to build as much as possible. What would the approximate compression ratio be with a 3mm? Normally I wouldn't ask such a common question but 3mm hasn't been mentioned yet in this thread. Thanks!

 

[IJ.]

What are the benefits or flaws of using a 3.0mm MHG? My buddy just bought a prebuilt 7m with an HKS 3.0mm head gasket and plans to build as much as possible. What would the approximate compression ratio be with a 3mm? Normally I wouldn't ask such a common question but 3mm hasn't been mentioned yet in this thread. Thanks!

You can potentially make more power on the top end by running more boost on the same octane fuel, low end suffers and quence/squish isn't optimum so fuel mileage will drop.

From memory mine was in the low 8's with an uncut Head/Block combination but any machine work will affect this.

 

[D.J.T.]

I have 198MM Block & 116MM Head so this would mean i need a 1.87MM head gasket, would a 2.0MM do? It's my first time working on a 7MGTE. Only thing that looks familiar is Oil pump lol.

My Calculations:
STOCK = 198.5MM+116MM+1.37MM = 315.87MM

My situation = 198MM+116MM=314MM

315.87MM-314MM= 1.87MM

 

[Volvospy]

Anyone used SIP racing mhg before? Apparently they have the thickness I need which is 1.4mm. Any sugesstions would be appreaciated.

 

[IJ.]

I have 198MM Block & 116MM Head so this would mean i need a 1.87MM head gasket, would a 2.0MM do? It's my first time working on a 7MGTE. Only thing that looks familiar is Oil pump lol.

My Calculations:
STOCK = 198.5MM+116MM+1.37MM = 315.87MM

My situation = 198MM+116MM=314MM

315.87MM-314MM= 1.87MM

2mm is a default thickness that works well for these engines, I'd go for it.

Anyone used SIP racing mhg before? Apparently they have the thickness I need which is 1.4mm. Any sugesstions would be appreaciated.

More than likely a Cometic Rich has made for him so all good.

 

[ZoomZoomZoom]

Your Grumpiness -

I have a stock block and a rebuilt head (from a company with a good rep). If I want to go MHG, I want to go ahead and mill the block because in its current state its likely not perfect enough for a MHG, but fine for a stock gasket, correct? And perhaps have the head double-checked to make sure it is perfect as well, right?

thankya!

 

[D.J.T.]

2mm is a default thickness that works well for these engines, I'd go for it.


More than likely a Cometic Rich has made for him so all good.

after about 4 months i get a reply... lol. Im using Fel-Pro HG.. 2K miles on it & no problems yet. Ill be Reviving the MK2 so when & if it blows i have the transportation ill need while it gets repaired. This time ill be getting ARPS, machined block, ETC.. & the MK2 Beats my "El Cheapo Honda" suggestion i give to everyone

 

[IJ.]

Your Grumpiness -

I have a stock block and a rebuilt head (from a company with a good rep). If I want to go MHG, I want to go ahead and mill the block because in its current state its likely not perfect enough for a MHG, but fine for a stock gasket, correct? And perhaps have the head double-checked to make sure it is perfect as well, right?

thankya!

I pretty well machine every engine these days it's just not worth the risk on a 7M as they're all getting on

after about 4 months i get a reply... lol. Im using Fel-Pro HG.. 2K miles on it & no problems yet. Ill be Reviving the MK2 so when & if it blows i have the transportation ill need while it gets repaired. This time ill be getting ARPS, machined block, ETC.. & the MK2 Beats my "El Cheapo Honda" suggestion i give to everyone

Should have waved ya arms or something

 

[ZoomZoomZoom]

My understanding is that the front timing cover plate should also be sent to the machine shop along with the engine so that it fits properly after the engine is decked.

Thought I would throw that in the discussion because its rarely mentioned in HG threads.

 

[IJ.]

My understanding is that the front timing cover plate should also be sent to the machine shop along with the engine so that it fits properly after the engine is decked.

Thought I would throw that in the discussion because its rarely mentioned in HG threads.

Good point first post ammended

 

[zambini]

Hello fellow coolant burners,

Recently, i blew a head gasket beating on my car during the last 100 miles of a 350 mile road trip. Didn't realize I was blowing smoke until i hit city lights, and as far as i can tell, i "only" drove the car about 20 miles after i knew i had a problem. The car has been parked and is currently back home in KY, where I was leaving it for the winter. (I live in Cleveland OH.)

I'm one of these types that isn't going to have the time to pull the block and have it machined while I'm at home fixing it over break. Assuming it isn't noticeably in need of machining, I do not plan on having the block decked. I was planning on running a MHG, but it appears that would be a terrible decision, given my chosen course of action here.. I DO have a stock HG I bought from the dealership lying around. So now it appears that I may be able to use it.. the thing that sucks here is the fact that I'm going to have the head machined down most likely.

Does the use of a composite stock gasket help my cause in terms of tolerance for HG thickness? (since they're more likely to seal with a non-machined block surface?) I'm assuming compression ratio is a completely independent consideration and will ultimately be affected by the machining of the head, regardless of HG material.. Therefore I'm going to have to get a thicker Composite Gasket. Right? Rendering the Toyota gasket useless for my application?

I'll be returning home with the intent of fixing the car with haste in about a month, so whatever I need to order, I need to order it now. How do you guys recommend I handle the situation, since I won't be machining the block? Most of this thread addresses MHG issues, but there's not much here regarding the use of Composites.

As always, excuse my ignorance please.

Aaron