Infamous 420a HG leak problem. Question on headbolt

[scirio]

So I have that infamous 420a headgasket oil leak and time after time I keep reading on here and 2GNT to get the bolt cut a mm or so. I called a machine shop today becasue I am doing the maintenance tomorrow and some old know it all fart was like " CAnto be done, that'd be stupid, I machine heads all day and never seen that problem. I'd charge you $100 bucks anyway but those are strech bolts, your an idiot yadayadayada I'm an ass" Well I was poatient and I just wanted them to cut it and keep the taper. What do I do.

 

[Doug99RS]

The problem is due to the headgasket design and not the fault of the bolts. The bolts are Torque-to-yield. They are supposed to be tightened to a specific torque (found in the HG box of gaskets from the dealership) and then turned 1/4 turn more. This will stretch the bolts a little. Depending on the conditions of the headbolts (which you are to inspect when you remove them) you may be able to reuse them. For high compression or forced induction applications you should always replace these head bolts.

The problem lies in the design of the original headgasket. It is composite in nature and does not transfer heat nor expand properly. The problem we had with the gaskets was that the aluminum head expanded at a different rate than the cast iron block. This caused the gasket to move around thus increasing the chance of leakage. The oil passage design in use on this engine only aggrivated the condition. Introduce a high pressure oil passage to the area of a gasket that is already compromised by design and you now have a leak.

The multiple layer steel (MLS) headgasket design has... MULTIPLE LAYERS of steel that help transfer heat and that have better sealing qualities than the original design. In addition to that, the use of the Headgasket sealant spray (similar to copper coat)adds an additional sealing quality.

The combination of the MLS HG, the spray sealant and the revised torque specs will prevent additional leaks from ever occuring to your headgasket sealing point. The only problems you will need to watch out for is excessive pitting due to electrolosis and from the remains of the old composite gasket. Do not use metal scrapers, course sandpaper, razor blades or die grinders with anything OTHER than a white roloc bristle brush. Use of these components will cause gouging.

You can reuse your head bolts, just as they sit, so long as they are not stretched or rusted up.
Doug

(Tiny typo, fixed.)

 

[SnoopySLR]

It would be pretty noticable if they were streached, correct? I used the same bolts, and the looked ok. I think I blew my piston rings, cause I'm pushing 25-35psi on each cylinder right now. My concern is, maybe I just need new head bolts. I'm rebuilding this winter, but it sure would be nice to drive it a little more right now. Also, if I get ARP HeadStuds will I need to replace them each time I pull the head? I don't think so, but need confermation. Thanks Doug!

 

[Doug99RS]

25-35psi on each cylinder right now. My concern is, maybe I just need new head bolts.

Um... 25-35 psi on the stock bottom end is what your problem is. You probably did blow out your rings. Maybe the headgasket too. Regardless I don't think you hopes for a temp. fix is going to work out for you too well. The head bolts don't typically stretch unless they've been over-tightened or used too many times. The ARP headbolts are reusable but you may need to talk with ARP about the correct set for this application.
Doug

 

[SnoopySLR]

Thanks. I didn't think it was that, but I was hoping.