Hi again,

I'm working on a 4.2 I rebuilt several years ago but had to let sit for various reasons. After some initial fuel problems I was finally able to get this old XJC running. However, It wouldn't take a tune and vacuum readings were all over the place. Also, after running 10 minutes coolant was leaking from the expansion tank cap. After cooling down, noticed oil in the coolant. Did a compression test to see if the head gasket blew. No. 6 (front) cylinder had zero compression! All other cylinders had 140 lbs/in. Pulled the head thinking maybe I got a defective head gasket. Head gasket is pristine, maybe to pristine, doesn't look like it was ever tightened down. However, I'm sure I followed the torque specs when I put it together. I also noticed that some of the acorn head nuts were threaded all the way down because 4 of the studs broke loose when trying to remove the head nuts. Is it possible the studs were stretched so much that I got false torque reading on a bottomed out acorn nut during torque down? Anyone seen this problem? Is this a problem peculiar to Jaguar engines? In all the years I've been wrenching, I've never seen studs that pass all the way thru the water jacket and screw into the floor of the block.

I'm ordering a new head gasket, but am not sure how to proceed. Don't want to repeat my mistake....

Thanks,

Steve

 

There is a lot to tell you but it's late and I'm going to bed, however, it sounds like the engine is in need of some serious work. If you have the head off, check for block cracking between the bores. It also sounds like the long head studs that pass through the coolant need replacing. Another check to make is corrosion of the timing chest cover where the water passage is formed. The wall can corrode if previous owners have neglected coolant changes, thus allowing oil into the water, (and vice versa !!).

Other thing is that it is essential to make sure the long head studs are in the right locations. Some (I think 4) are slightly longer to allow the engine lifting brackets to be fitted. The studs must be screwed fully in and the nuts checked to make sure they don't bottom and fail to clamp the head. Did you skim the block at the rebuild ? If you did, did you also make sure the timing chest cover was bolted up so it got skimmed too ? If you didn't the timing chest cover may protrude and prevent the head from being bolted down properly.

Or it may be none of the above !! Doug Dwyer should be along soon with more advice. He is the real expert on this forum, as it's a long time since I rebuilt an XK engine.

 

Fraser covered all the bases I can think of.

Were the studs previously removed? If so, Fraser's remark of "The studs must be screwed fully in and the nuts checked to make sure they don't bottom and fail to clamp the head." is especially valid. If the studs were removed the holes MUST be cleaned before they are reinstalled.

I did a head gasket job once and found that the nuts I ordered (fancy chrome jobs) were different than the originals. They were not as deep....and they bottomed out before clamping the head, just as Fraser mentioned

If the head isn't being clamped then a double set of washers might be all that's need to solve the problem.

Cheers
DD

 

I checked for cylinder cracks between bores and there are none. I would expect that if there were cracks between bores, I would lose compression in 2 cylinders?
The front engine lifting bracket was on the left side (when viewing the engine from the front of the car) of the engine along side no. 6 cylinder. The rear engine lifting bracket was on the left side of the engine along side no. 1 cylinder. Does anyone disagree with this placement?
Yes, the block was decked and the head was skimmed. The timing chest cover sits about .005" proud of the deck. I would expect the head gasket to be able to take care of this difference since it measured .051" after removal. Does any one know the expected thickness of a "crushed" head gasket?
I don't recall any unusual wear in the water pump cavity in the timing chest cover when I assembled the motor. Also, I didn't see any evidence of water in the oil which is curious. I cracked the oil sump and let out a few oz. of oil and it was clean.
I drained the block completely thru a block drain plug. I then used an old hair dryer to blow warm air thru the water jacket inlet ports on the deck to gently evaporate the remaining moisture. I dropped one of the studs back in place and was only able to thread it down about half the thread length by hand. I then backed it out and noticed oily moisture on the threads. What do you guys use to clean out the thread bores at the bottom of the block?
Double washers... wow! sounds easy and makes sense. All things being equal, if .020 were removed from the deck and .020 were skimmed from the head, then, a .040 washer should have been added at re-assembly to compensate for the new (lowered) height of the head bolt bosses....

Thanks,

Steve

 

Make sure stud threads are clean. Use new ARP studs or factory and make sure, as above, long and short studs are in correct place and a dab of lube to torque specs. Shim acorns where appropriate.

 

I had a special tool made up using a tap welded to the end of a piece of round bar, with a tommy-bar welded on the end. This then went down the stud hole and allowed me to clean out each threaded hole. I also had the core plugs out so I could see what was going on at the bottom of each stud. This meant that if the weld broke, I could get at the tap to remove it !! I was working on a bare block on an engine stand, so it was an easy job. It is very important with these old XK engines to really flush out the water jacket, by taking out all core plugs, plus the core plate at the rear and poke around with a piece of wire whilst flushing.

 

I put the 4 studs back into the block in the same positions they were pulled from. Then took a measurement from the deck to the first thread on each stud. They were roughly 4.625" to 5.125". The height of the headnut bosses measured 4.910 (front) to 4.860 (rear) with no deviation side to side (.050 runout seems exsessive?) The washers measured .125 and the gasket measures around .050. So, start with the gasket, add the head height along with the washer it all stacks up to 5.085 to 5.035, which means the stud at 5.125 was not clamping at all and many others were marginal. After swapping a few studs around replacing lowest with highest and vise versa, I got all the studs in the 4.75" to 5.00" range with the longest at the engine lifting points. I will add some height with additional washers and this should even out the clamping and hopefully keep the water and oil from mixing.

The loss of compression in cylinder 6 had nothing to do with clamping force. I sprayed some cleaner into the no. 6 exhaust port to try to see if there was any cracking and the cleaner spilled straight through to the combustion chamber. The valve should have been completely closed. I pulled the spring and rotated the valve in the seat and it was quite evident that the valve was bent. The only explanation is that I must have placed the head on the bench combustion chambers down after the head was refurbished. Even though it's my nature to never do so, I can't imagine what else may have caused the valve to bend.

Thanks for all your help,

Steve

 

I also today remembered another thing I did to clear out the stud holes in the block.

I got a piece of plastic tubing, and cut a notch at the end then attached the other end using masking tape to the end of a vacuum cleaner crevice tool. I then got the cleaner going and poked the tube down each stud hole into the threaded hole, and vac'ed out as much crud that I could, before using the tap tool.