Head gasket

Nick,

From memory the ex factory gaskets came in 5 different thicknesses. For whatever reason the spare part replacements only came in 3 different thicknesses. Once again from memory it was something to do with piston protrusion above the block deck. When I replaced the head on the original engine in my 91 model I went for the next available thicker one. I can't remember what notches were involved but I thought the replacement gaskets came with 1, 3, or 5 notches but way too long ago.
I don't remember being able to detect any difference in performance or starting.

Cheers
Pop

Performance will affected. By having a thicker head gasket, this would give more clearance and reduce the comrpression ratio. How much drop in output is difficult to say, but there will be some drop. Compared to a blown head gasket, the difference will be huge anyway and you would not know if it could have been better or not.

Yes, it will affect the performance of the engine - only moderately - but the greatest potential for change in performance will be in starting, particularly on cold mornings.

Diesels rely on several things for good, easy starting - the primary one being adequate cranking speed by the starter motor.
The next most important thing is adequate compression pressures when cranking, which is affected by compression ratio and proper valve sealing.

A thicker head gasket will reduce the compression ratio by enough to change starting characteristics from easy starting to hard starting.

The recommendation from ACL is to utilise the same number of notches (thickness) in the replacement gasket, as in the original.

Possibly more importantly, is that you do a piston protrusion check accurately on all pistons, and fit the thickness of gasket as indicated in the ACL chart.

ACL chart

Cheers, Ron.

Original factory engines came with a selection of 1 through to 5 notches.

The replacements from memory and according to ToyoDIY gave a choice of 1, 3 or 5 notches.

So supposing you found your gasket had 4 notches.

Would you use the 5 notch and lose all that compression, as others seem to think will happen, or go to a 3 notch and risk the pistons getting up close and personal with the cylinder head??

In your case Nick, I would chase up a 3 notch as per original if possible. If not the choice is yours.

Head gaskets were made in 5 grades
1 - 1.25mm
2 - 1.30mm
3 - 1.35mm
4 - 1.40mm
5 - 1.45mm

only grades 1, 3 , and 5 are used in rebuilds based on the piston protusion as measured.

Gasket 1 is used for protrusions under 0.525mm
Gasket 3 is used for protrusions from 0.526mm to 0.625mm
Gasket 5 is used for protrusions over 0.625mm

DO NOT re-use head bolts on a torque to yield engine. Buy new bolts and from memory its about 38NM (check that) then 2 times 90 degree pulls in sequence on about 28 head bolts and your arms will feel it I had a guy pulling the bar as i was pushing on the last pull.

Hope this makes it clear and helps you.