Block finish and head gasket mating (mhg or graphite?)

[Kedderz]

As some of you know im undertaking my first major mechanical work by myself, of which is a new head gasket on a 7mgte.

Ive taken the old gasket off and im up to the stage of prepping the block. Ive used a gasket/plastic scraper to get rid of alot of the gasket BUT there is still residual left on the block. It feels "flat" to the finger but to a mhg it of course isnt ;-)

The real question I have is just how important is the finish of the block when using a mhg?
and How forgiving is a standard oem replacement ie Graphite unit?

[fixeruperer]

"how important is the finish of the block when using a mhg? "

more than anything, there should be a stronger word than important just for surface finish for mhg.

and being a 7m and prone for the odd blown head gasket and your gonna belt the shit out it youd wanna do everything, face the block and head, check over the head, throw in some arp studs.

the graphite gasket is a bit more forgiving but its days are numberd.

measure everything up (head/block straightness) see what clearances you got with a straight bar and feeler gauges.

[Kedderz]

The head is being pressure tested + disassembled + valves checked + skimmed by a shop and will be ready by tommorrow.

Does having the block decked mean engine means block comes out of the car correct?
I think its prudent to have the car towed and block decked. I guess it will be better to do it once, and do it properly.

[fixeruperer]

yeh means motor out but then comes the snowball effect becuase you may aswell rebuild it hehe.

but check it for straightness you might get away not doing it.

[Kedderz]

+ rep thanks mate.

Ill chat to the head palce tommorrow and see what they would charge to take the motor out. I have neither the skills nor the equipment to do so. ;-)

[IN 05 NT]

block decked means you give them a block, no rods/pistons/crank,

as mentioned above, mayaswell rebuild the lot while its apart if your doing it.

VRS kit will be posted 2moz, (sorry havent had the chance yet!)

edit, if you dont skim the block, use the graphite.

Blake

[Supra-Jim]

From memory i believe the Cometic MLS (Multi layer steel) gaskets are a little more forgiving on surface finish than other metal gaskets. According to their website (www.cometic.com) the necessary/recommended surface finish for proper sealing is 50Ra.

I have 'heard' that the standard Toyota finish on the 7M block is good enough for this, but this was internet whispers, so i would recommend getting it cheched out. Maybe see if you can have your block surface measured before going to the effort/expense of having it pulled out and dismantled.

Stolen from the Cometic website:

What is MLS?
MLS stands for Multi-Layer Steel. MLS head gaskets are comprised of three layers of stainless steel. The outer layers are an embossed viton coated stainless steel providing a superior seal with excellent rebound characteristics and are corrosive resistant. MLS head gaskets reduce bore distortion and withstand extreme cylinder pressures.

What surface finish is required to us an MLS head gasket?
A surface finish of 50 RA (roughness average) or finer, is recommended for a proper gasket seal. Anything rougher may conflict with the gasket design.

[jimmmayyy]

I had mine decked, then I gave it a rub with a wetstone checking for straightness all the time. While you're going as far as putting in a new HG, fresh head etc, you may as well take to block out and do the whole thing properly. I dunno what tools you have, but it's not a difficult job at all.

Any other motor i'd say go for it, but being a 7M you'll want every bit of 'insurance' you can get. 7M's also seem to have a common habit of munching bearings from oil surge/starvation.. so I say why not go and freshen the whole thing up.

I managed to get mine completely done for a shade under 2000, which included new short block +machining, checking and machining of head, Cometic HG, and ARP studs. You can save alot doing it yourself.

[Kedderz]

I have decent tools, its being scared of the unknown that makes me think i should tow it to a rebuilt place and get them to take out the block, machine + replace bareings.

I can follow guides not a problem, but trying to figure out something Ive not attempted before I will be scared to break something or worse, do damage.

Remeber the last job like this was on a camira when i was 8 years ago and all I did was help my dad.

I have the arp bolts/cometic mhg already, so thats not a problem. Also if the block comes out theres the school of why not new pistons + rods etc etc etc, flow on effect!

[YLD-16L]

Ive used a gasket/plastic scraper to get rid of alot of the gasket BUT there is still residual left on the block.

If you decide not to get the block decked then grab a can of the gasket remover to thoroughly clean the block surface, it's available at most parts stores and will at least give you a clean surface if you decide not to get it decked.

[Kedderz]

Yeah ill be doing that after ive visited the head place today. Im leaning towards decking block as, do it once, do it properly as my mum always said.!

[abently]

If your going to sell the car in a couple months time, then I'ld tell you to leave the block in there. But if your going to keep it for a few years then pull it out ?

Though from your responses, you sound too sensible to keep this sort of car for too long knowing it will always be costing you $$$.

[Kedderz]

This car is a project, im wanting to do as much as I can myself, safely.

Its not going to be a daily or anything, its just a weekend cruiser and something to occupy my time ;-)

[oldcorollas]

if you are just cleaning the block..razor blades (the 20mm? wide snap off ones, or stanley knife ones) make great scrapers on cast iron. on alloy they can dig in, but on a block they work well for scraping shit off

[jeffro ra28]

Considering a factory surface grind is basically equivilant to a 5 year old weilding a 9 inch angle grinder ill jump on and support the claim that you should get the block decked for MLS gasket.

Also, on another note, has anyone ever considered using o-ringed block and a composite gaket? This was something i was forced to do on an engine with no MLS gasket available and copper gaskets would not seal. It has held up to 22 psi and still going well. This may be an option for you, but if your going for MLS anyway its kind of pointless.

IF say you dont want to remove the engine, it would be possibled to get the block O-ringed (hand held HSS cutter jig) whilst in the car and then use composite gasket which works very well. Any performance machine shop should have this tool.