7M-GE headgasket: Composite vs MLS (multi layerd steel)

[toyota.s]

While my engine block and internals are sitting in my storage waiting to go machine shop, while I wait I'm shopping around for parts. Should I go with composite head gasket or MLS? I plan on just doing a stock rebuild on this 7M-GE supra no power adders (stock horsepower) and factory red coolant. Arp headstuds 20-40-60-80 torque sequence.

Some sources say the composite head gaskets were the problem along with the under torqing. Some say composite do a good job for factory applications. Other sources say MLS do a better job in general. Leaves me indecisive, If I do go MLS I plan to get it from cometic. If I go composite I already have one oem from a toyota gasket set.

 

[Bru]

A MLS gasket requires very smooth surfaces if your machine shop is up to that. Bear in mind that Toyota allows 0.010" removed from both services total before a thicker head gasket recommended. Stock head thickness is 116 mm or 4.567". Stock block distance from the main bearing saddle to the deck is 198.5mm or 7.815". The machine shop can get you those measurements if you request it. Be sure to have your front aluminum cover cut with the block otherwise there will be a step there where it should be flat for the gasket to lay flat. Check the valve lash, especially if you have them ground because machining can change it. You may have to result to swapping the adjusting shims around to get them all in spec. Instead of using a metal head gasket, I'm using an old school 0.020" solid metal shim gasket underneath a standard Toyota head gasket. In that case I sprayed the bottom of the shim gasket with Permatex copper spray. It's lasted 10 years and 30K miles so far. A quick way to tell if your head has been cut before is to look at the place where the thermostat standpipe connects to it. it should be rounded, but if it's flat it's been cut before. See photos. You can do a quick thickness measurement with vernier calipers. Here's a link to the online repair manual if you don't already have one: Click here to go there. The ARP studs and nuts needs a thin wall socket o fit over the nuts because it's in a tight space. I used a craftsman 50671 deep well 3/8 drive, 12 point, 14 mm socket. They are available on eBay for about $6 delivered.

 

[toyota.s]

A MLS gasket requires very smooth surfaces if your machine shop is up to that. Bear in mind that Toyota allows 0.010" removed from both services total before a thicker head gasket recommended. Stock head thickness is 116 mm or 4.567". Stock block distance from the main bearing saddle to the deck is 198.5mm or 7.815". The machine shop can get you those measurements if you request it. Be sure to have your front aluminum cover cut with the block otherwise there will be a step there where it should be flat for the gasket to lay flat. Check the valve lash, especially if you have them ground because machining can change it. You may have to result to swapping the adjusting shims around to get them all in spec. Instead of using a metal head gasket, I'm using an old school 0.020" solid metal shim gasket underneath a standard Toyota head gasket. In that case I sprayed the bottom of the shim gasket with Permatex copper spray. It's lasted 10 years and 30K miles so far. A quick way to tell if your head has been cut before is to look at the place where the thermostat standpipe connects to it. it should be rounded, but if it's flat it's been cut before. See photos. You can do a quick thickness measurement with vernier calipers. Here's a link to the online repair manual if you don't already have one: Click here to go there. The ARP studs and nuts needs a thin wall socket o fit over the nuts because it's in a tight space. I used a craftsman 50671 deep well 3/8 drive, 12 point, 14 mm socket. They are available on eBay for about $6 delivered.

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Deeply noted. I do plan to do the works block decked with timing cover. Good tip on the head for the Stanpipe.

Since I'm using cometic MLS gasket, but not adding power. Would you still recommend using arp studs instead of bolts?

My original plan is to use arp head studs but use the factory washers due to other user's telling me they had to fitment issues with arp washers. I plan to torque in sequence 20,40,60,80 ft lbs. So much information on other forums and now I've gotten lost.

 

[Bru]

ARP studs are an upgrade over stock Toyota bolts. ARP also makes a bolt set. I had no issues with the washers that came with the ARP studs and nuts. If the center hole is chamfered, be sure that it's facing up. Here's a link to the ARP question and answer page. Click here to go there. There's a debate on other forums about how tight you should go with the studs and nuts. The paperwork I received at the time said 90 so I went to 90. If your aluminum head is getting soft with age, then closer to 75 would be the safest play. I haven't had any issues. It's a good idea to chase out the holes in the block with a tap or a old head bolt that has a groove cut in it to remove carbon, also to soak out anything at the bottom. If you're going to use ARP main journal studs and nuts, be careful that the oil sump pickup tube does not hit one of them before the pump is tightened down. I had to make a modification in the tube by denting it and grinding a bit from the flange that bolts on to the pump so that there was clearance.

 

[toyota.s]

ARP studs are an upgrade over stock Toyota bolts. ARP also makes a bolt set. I had no issues with the washers that came with the ARP studs and nuts. If the center hole is chamfered, be sure that it's facing up. Here's a link to the ARP question and answer page. Click here to go there. If you're going to use ARP main journal Studs and nuts, be careful that the oil sump pickup tube does not hit one of them before the pump is tightened down. I had to make a modification in the tube by denting it and grinding a bit from the flange that bolts on to the pump so that there was clearance.

OK got it. I plan to use stock main cap bolts. A few users said stock main cap bolts are fine unless you add horsepower and torqing spec will change as well.

 

[Bru]

The only reason I used the ARP main studs and nuts is that they came with a donor engine. I also used ARP connecting rod bolts and nuts from that same donor engine. If you want to sleep at night you can check the oil clearances everywhere using plastigauge. Most auto places have it. It's mentioned in the rebuild manual.

 

[Bru]

Some other things worth noting are checking the piston to cylinder wall clearance (0.003 - 0.010"), and ring end gap. Piston compression rings are marked showing which side is up. Stagger the end gaps so they don't line up. Be sure your machine shop puts a crosshatch on your cylinder walls. The purpose is to bed in the compression rings. Change the oil after 50 miles and then at 500. I use Castrol GTX 10W40 dino oil. You can get a deal on a case of 10 Toyota oil filters searching on eBay. 90915-YZZD1 made in Thailand. I've had good results using Permatex Ultra Black silicone for places like oil pan, valve cover gasket. Use an assembly lube when putting things back together. Permatex Ultra Slick # 81950 is a good choice. Be careful when tightening down the thermostat cover 10mm bolts, they strip easily. Be sure you use the correct bolt that retains the oil pump shaft to the block. The clearance there is very tight behind the aluminum cover.

 

[toyota.s]

I do plan for the machine shop to have a crosshatch finish in the bores. Hoping that's all they need to do with the bores, I don't plan on boring out.

 

[Bru]

You can check the piston to cylinder clearance even if it's with a Harbor Freight vernier caliper. Machine shops use a bore gauge that fits down in the middle of the bore. You could request that information or include the pistons for them to measure as well to get the difference. Ring end gap can be measured using a set of feeler gauges with the individual rings in the cylinder you plan on putting them in. Rebuilding an engine is like being a machinist. The more you stay in tolerances, the better the chances that the engine will last. Here's a manual reference: Click here to go there.