Do heads normally need machining when replacing HG?

[bebbetufs]

It's official; I am cursed. The turbo blew again, third time in three years. I'm pulling the engine to fix as I have to reaseat the leaking oil pump as well.

I will install a wide fire HG as a precaution. Original gasket is 63K miles. Compression is great and there are no oil leaks. Can I assume the head is straight and order a standard thickness gasket?

What MUST be replaced when doing the HG? I did the valve stem seals and all other seals two years (1K miles) ago when I pulled the engine due to another busted turbo. I'm thinking exhaust manifold gaskets, cam tower gasket, nuts and washers and that's it.

[carlege]

if there is nothing wrong with the head i would reuse it.

[johnkoawood]

If the turbo is blown, why are you replacing the head gasket?

If the head gasket is blown, with only 1000 miles on the engine, you need to have the head checked... and possibly decked (if it is within spec allowance to do so)

You may also want to have the block checked...

[nize]

i'm curious and we need more details about this. how/why did the turbo blow three times in one year, and why do you have to replace the headgasket?

was the turbo a rebuilt or new? what make/model? who did the work? etc. etc.

[bebbetufs]

Thanks for answering.

I want to change the HG for a wide fire gasket for peace of mind. The gasket is 20+ years old and a new one is relatively cheap. I want to be able to exploit my A-tune for what it is worth. I won't do it if it is at all likely that the head will need machining.

Turbo blows (to my pride and wallet):
1. Loose metal washer got into intake. Probably there when I bought the car.
2. Turbo kicked the nut off. (My DYI rebuild (could be the cause).
3. Still to be determined. Possibly a kicked nut as it went extremely quick. This was a workshop rebuilt complete unit as the one I rebuilt myself was thrashed.

[nize]

assuming you're still using the kkk turbo, are you sure the turbo is getting sufficient oil flow? how about sufficient coolant flow?

bad lubrication or coked up oil due to excessive heat (lack of water cooling) can cause the turbine shaft to seize when the turbo spools to 150,000 rpm, which can cause the nut to fall off.

you'll also need to be 100% sure any rebuilt turbo is properly balanced and comes with a warranty.

it might have been cheaper/easier to just buy a new garrett double ball bearing turbo, and could still be.

[bebbetufs]

I went with the KKK to keep things stock and (I thought) reliable . I will definitely consider the Garret now, but I'm still hoping the rebuilder will take responsibility. I have not spoken to them yet, I will pull the engine and take a look first. All I know is that I have done everything by the book and been super careful and kept everything super clean when installing. We can troubleshoot the turbo disaster when I have spoken to the rebuilder.

I'm ordering parts now and need to make a decision on the HG, so what is the consensus, no machining needed?

[nize]

if the head gasket didn't fail, and if the engine didn't over heat (causing head warping), machining the head is not necessary.

as for what needs to be replaced with a head gasket job, lindsey sells a very convenient 'head gasket set' that includes everything you need.

[bebbetufs]

Thanks Nize.
I think the cylinder head set is too comprehensive as I changed every single gasket, including valve stem seals, when the first turbo popped. The only thing I didn't do was the HG so I want to remove as little as possible to get to it. Is there anything that must come off except for the camtower and the head itself to get the job done?

[MarkRobinson]

Machining: no, cleaning to ensure a smooth deck before reinstallation: Def. Use a red or green scotchbrite & work away, ensure there are not pits (electrolysis-enduced damage) in the head at the ring-sealing surface.

[bebbetufs]

Thanks for replying Mark. I will go ahead and order what I need.

Just a heads up: Although many people have used Scotch Brite successfully to clean flanges and and other surfaces I would personally advice against using it in any area where any dust may enter the engine or oil passages. The dust is super abrasive and a tiny amount may cause huge damage to bearings and journals. If you decide to use it make sure you clean up twice as well as you think necessary. Read more here.

[MarkRobinson]

Well yes it is, but I power-wash my head(s) before reinstallaton: all ports & passages & then use a pressurized air blower to remove all extra water before starting the head reassembly. No problems in 13+ years of playing that way.

[nize]

fyi, if you want a stock factory 951 head gasket (only), let me know. i have a few spares laying around that i don't plan to use since my motor is now a 2.7 bore.

note this is the stock porsche factory headgasket for 951, not a widefire.

$20 and shipping from seattle, wa.

[bebbetufs]

Thanks, but I think I want the added security of the WF.

[89-944NA]

If you want real piece of mind on the HG, use the Cometic MLS HG....I have two engines sitting in my garage that have blown wide fire hg's from running just a tad to much boost. I blew one, and a friend blew the other (to my advantage...picked that engine up complete with all accessories for just $400).

[bebbetufs]

Thanks for the tip. From what I read the MLS gaskets can be difficult to get right. I think I'll stick with the composite gasket for simplicity. I'm planning to use a stock K26/8 and I will keep it below the factory over-boost limit.

[nize]

this has been discussed before. if you overboost to knock/detonation, would you rather have the gasket fail or the engine (pistons/rods) fail?

[MarkRobinson]

Agreed with Nize: this has always been my logic: never lost an engine with over 20 modified Porsche's.

[bebbetufs]

this has been discussed before. if you overboost to knock/detonation, would you rather have the gasket fail or the engine (pistons/rods) fail?

Is this meant as an argument against upgraded gaskets in general or the MLS gaskets only?

[MarkRobinson]

Not my arguement, however like Nice said, if something "needs" to give so the rotating assembly doesn't give due to overheating, detonation, then make it a maintenance-item like the headgasket, in lieu of a mechanical failure that might trash the entire engine.

The MLS gaskets are not really designed to give much, putting more heat/stress on the piston. A wide-fire ring gasket is only widened on one edge of the ring, making it stronger, but the material is still OE therefore the gasket can/will give in time.