Loose head bolts?

[keenyoung]

I bought a 2003 Discovery 2 with a blown head gasket. The gasket blew out of the two inside cylinders on the right bank outward toward the exhaust manifold.

When I pulled the head, all 5 of the head bolts inside the valve cover required a 3 foot breaker bar and serious muscle to break loose. All 5 of the head bolts outside the valve cover (the ones above the exhaust manifold) were removed with a 3/8 ratchet with no breaker bar, and just a small push.

Has anyone ever seen head bolts loosen themselves on this engine? Or did the overheated engine put enough stress on the bolts to stretch them? Or did the previous mechanic forget to torque the bolts?

The blown head gasket was a composite, so I assume it has been fixed once before. Also, the head is clearly warped at almost .004" out of straight.

Thanks,
Keen

 

[joey]

Sounds to me like it was overheated several times causing the issue you described.

 

[howardduff]

There is a flat area adjacent to the spark plug holes on the side of the head where the gasket was blown out. You should be able to remove at least 0.010 in. (0.254 mm) of material from the joint face to flatten out the head. Take it to a machine shop in your area that machines cylinder heads, they can set it up and face mill this surface. This will not degrade the combustion chamber volume if you are close to the nominal dimension in the first place. They usually take an average of all 4 button depths for the original measurement in the first place. I was an engineer on a cylinder head line for 20 years and this was part of the process. By the way you don't want a ground surface because the gasket will tend to slip if is too smooth. Good luck, a new head will be expensive.

 

[keenyoung]

Thanks for the replies. I believe I know what happened to this Rover. I pulled the timing cover to inspect the oil pump (2003 Disco, right?) Turns out the timing cover gasket was blown, and a bunch of coolant poured into the crank case. PO apparently had no idea there was a problem until it over heated, expanded the aluminum head, and stretched the outer head bolts past their yield point, and the gasket blew.

I have taken the head to a proper cylinder head shop, and had it milled. New gaskets and seals all around. New oil pump gears too. Hours of stinky dirty cleanup and gasket scraping. Yuck.

 

[BeemerNut]

Original 14 bolt heads once the outboard head bolts were torqued down this caused the head to be pulled down on the exhaust side unloading the clamping force under the other bolts. Blown gaskets the problem afterwards.
Install the four outboard bolts but only torquing them down to snug only preventing cocking the head as well keeping those bolt holes from collecting dirt and water.
Later heads only came with 10 bolt heads, 4 bolts not required to maintain even clamping pressure, problem solved.
Stainless embossed gaskets were installed up to and including 1995 Rovers with a serpentine belt.
Sad part replacing with thicker composition gaskets lowers your compression ratio.
Installing later 96 or 97 heads of 28 cc combustion chambers regained compression when switching to composition gaskets vs 36 cc chambers of early production 3.9's.
Later 28 cc heads with steel head gasket bumped up compression app an additional 1/2 point. This only good in countries that have good gasoline.