I am sure you have all seen this before. But I figured since I am new here I would chronicle my build. It will help me keep moving forward on it and if I get stuck I might be able to get some in-process advice.

I have recently introduced myself. For you that didn't happen upon my intro; My wife purchased a 1990 XJS for our "couples therapy project" We knew we would have to go through the engine but the car is immaculate otherwise.

Here is the plan: Pull engine, drop front cradle, drop rear end, Touch up any issues with car and put her back together as good as or hopefully better than new.

Without ridiculous stars in our eyes I am following calvindoesnknow's 6.8 build with interest. Budget will control how extreme we build. Since for me labor is cheap and I have a great deal of machining experience with a shop or two available to me a large number of items will be done by myself. I have only built a couple of engines so I do have to keep my aspirations low as I really just want this to be a driver with low drama. I am hoping that this thread will inspire some that though about taking this on but also let you seasoned gents get a kick out of the dynamics (also feel free to redirect if you see me getting off course)

My aspirations: Get the engine over 400hp.

Things I would like to try: Serpentine belt system one belt should give me more space for deeper radiator and better cooling??

Final goal: Keep the budget under $10k. so far we are into it $2k

We started out removing all of the crap on the top of the engine in the hope of being able to pull the "A" or driver's side head and just do a gasket replacement. After trying unsuccessfully to remove the head we decided since we were into this basically half way through the engine we would just pull the engine and work on it in the comfort of my workshop instead of the garage.

I had to modify my engine stand by extending the front wheels 12" for a bit more stability and I put some nice large cast iron and rubber casters on it so that it would roll nicer and fit through the door of the workshop.

Mama pulled the engine accessories to reduce some dead weight after we mounted it to the stand.

The images so far are where we are currently at.

Oh! and one big question...Why is the engine not pulled out from the bottom while attached to the cradle? It seems like the way it was assembled at the factory.

 

Again I welcome you!
You could switch all the pulleys over to a single serpentine belt system, I believe the later 6.0's used them, but I'm not positive of that. However I don't think you'll gain any better cooling capability. As long as the stock radiator isn't clogged with leaves or plugged inside it is more than sufficient in keeping the engine cool. The OEM fans were problematic though as they became brittle with age and could fly apart. The fan clutch in mine went bad, so when I pulled the fan out I discovered mine was cracked and coming apart. I changed it with an electric fan from Advanced Auto for under $100 and it works perfectly.

The engine is certainly capable of making in excess of 400hp. It really depends how deep you wish to dig into your pockets. Having access to a machine shop certainly lowers the price threshold though! Bigger cams are available, better flowing exhaust, you name it.

I'll be following your progress!

 

Congratulations on embarking on this project together. And thanks for another opportunity to refer someone to WELCOME TO AJ6 ENGINEERING / AJ6 Engineering
I can't help you with your aspirations, but the people at AJ6 Engineering have been through it and their site may give you some ideas. Good luck, and please keep us posted on your progress.

 

I'd say using electric cooling fans would give you a lot more room for a radiator but then again if the old radiator is clean and has dual electrics on it, you won't need a bigger radiator.

Although it could be a good cold in terms of ease of maintenance. Replacing all four belts in annoying.

 

Good luck with the project. If you have not already done so, download and read Kirbert Palm's book on the XJS.

The engine was put into the car at the factory from above. I have a phto of the line to prove it. The reason is that the dressed engine is too wide at the top to go up though the lower chassis rails.

Greg

 

I appreciate the advice on the radiator. Everything I have read "on the internet" has really focused on how inefficient the radiator was. (you can't post anything on the internet that isn't true you know ) I will send the radiator off to the shop for an evaluation and a thorough cleaning. Currently this motor has a new engine mounted fan and the original electric fan. The shroud is a bit rough but it could easily be returned to as built condition.

 

Great article on your engine re-build. Hope you achieve your objectives.

I to own the XJS-HE jointly with my wife and share the joy of driving it.

Normally I take full note of all the advice given in this forum, but for once have to make some observations in regard to the lengthy debate about the "poor radiator design" of the XJS. Yes, we also had over-heating problems when we first acquired the car, read every article related to the subject and noted the many serious debates thereto.

If the "advice" had been followed we would by now have completely re-buit the entire cooling system at considerable cost. However my wife is strong believer in keeping the car absolutely original, hence we took the radiator out of the car to find that approximately 87% of the core was blocked. In addition we found that there was a heap of rubbish between the various condensors. Cleaned the radiator and put it all back in place as per original.

end result; simple - a car that holds designed temperature event in our 40C+ heat under all traffic conditions. Not bad for a car that is 30 years old and one that has "serious design faults in the cooling system".

Moral of the story and first port of call - check the condition of the original installation and don't get waylaid by design issues.

Bernard

 

ah I am feeling the pressure guys. 400hp is reasonable on the he motor, could be done with stock he heads, better injectors and maybe more cubic inches this might put you over your budget but have you concidered a 5 speed aswell? I did thar swap for like 3.5k with some seriously uprated parts.

 

Id say the stock engine with a 5 or 6 speed would probably be as fast or faster than a 400hp version with the stock 3 speed.

If the stock motor is bottlenecked by the 3 speed, just imagine a 400hp car. Not to mention gas mileage.

 

I'd gladly take 300 horsepower with a five speed manual versus 400 horsepower with a 3 speed auto :-)

Not that I'm an expert on V12 performance mods but I suspect any mods to take a 5.3 to 400 horsepower will result in a loss of low rpm power in exchange for high rpm power. This magnifies the disadvantage of a 3 speed auto.

Supercharging might be an exception :-)

If you have oodles and oodles of low rpm grunt ....which a Jag V12 doesn't....the problem wouldn't be so significant.

Heh heh. I drove a Corvette with a 390 horsepower 427 and a *2 speed* automatic. It flat-out hauled. The power/weight ratio and torque were so great it hardly mattered how many gears it had.

An XJS V12 is a different story.

Cheers
DD

 

Ah yes the venerable transmission debate. Over the past year we have been in deep debate regarding what to do with the car. Lumps, turbos, superchargers, trannys etc. A wise man made a comment to me last week that brought us back to reality. "Work within the potential of the car you will not be disappointed." I don't know why, but that simple statement pulled me back into focus. You all are doing a fine job of helping me stay there. We are going to rebuild the TH400 and give it a try. Since it is not a royally tough job to remove the tranny in the car we may consider a 700R4 somewhere down the line.

Last night I removed the cams and all accessories from the motor. Tonight I will be making the head removal plate so that I can lift off the heads. I will post some pictures of the condition once it is cracked open.

I would like to find a shop here in DFW that can bench test this motor before I put it back in. I am not coming up with anything yet. Any ideas?? I really want the ticket that proves the HP rating.

Thank you for the cooling system reinforcements!!!

 

I made two of the "short plates" to remove the head. after two hours of patient turning I have a 1/2" gap to share with all of you. I had soaked the studs with penetrating oil over the course of several months. I will make two more plates and give this another go. If that does not prove to be the solution I will go with the full plate. I was trying to save material and the "short plates" have been pretty successful with others.

 

1. Free up the exhaust (gut cats, remove a pair of resonators)
2. Free up the intake
3. Transmission swap (4 speed auto or manual, that's up to you)
4. ??
5. Profit.

Tons of $ leftover for cosmetics, ICE, etc.

 

if you dont have thw whole plate I wouldnt risk warping the head. the other thing you can do is pull the cam assembly off and use an extractor socket to pull the studs out.

this WILL require new studs. but if they are thar cardoded, you'll need new ones anyways.

 

WOO! HOO! Head off! I walked the "short plates" front to back like you would tighten down the head bolts (so that I wouldn't warp the head) It took another three hours but the head is off straight and undamaged. I am a little worried about the cam bearing studs though.

You can see the crack in the head gasket on the 2A cylinder in one of the images. Head looks good no erosion. Cylinder walls are in perfect order not a scratch on them the hone marks are still there.

So we are at a cross road. Stock this engine per wiki is 282 horsepower. For about $1000 in parts (gaskets etc) I can put her back together and focus on the other parts of the car like the 4 speed auto and complete suspension rebuild. After following calvindoesntknow's postings and the quick reading that I have been doing it looks as if my aspirations to get to 400 horsepower are going to run me about $500 minimum a cylinder. The pure economics side of things that is not a good price per horsepower.

My daily driver reminded me of something last night (2000 F250 diesel) climbed in after my boy's ball game and no power to the fuel pump. Thankfully some fuse chasing netted me success and a safe ride home but she reminded me that I should stay focused on getting and keeping my toys running.

That being said I will finish my humble pie and focus my energy on good thrifty improvements as recently suggested by Flint and anyone else that would like to share their findings.

Since I had a lot of time to stare down the intake port of this head I feel that match porting would be a good place to start with some elbow grease improvements. Mr. Palm and Mr. Bywater seem be adverse to any porting attempts. Does anyone have some documented proof of any gains? possibly images or diagrams of porting that you could direct me to??

 

Ah, for a minute there I thought that was a cracked block, not a cracked head gasket. Whew!

If you're not going to build the motor, there are other go-fast modifications you can make that would help from a performance standpoint, such as rear gears and a new/restalled torque converter, etc. They will give you a lot of bang for the buck!

 

Second head came of much easier. Only two hours of wrenching on that one. I am optimistic that the roughest part of the build is behind me. Please don't burst my bubble.

Mama did some preliminary cleaning of the sealing surface on the A head. We have some pitting in the coolant area showing up. My guess is about 0.06 depth on the worst one. three total and all in the coolant area not on a sealing surface. I am of the mindset to leave it alone. Welding it could warp the head.

 

I agree, it's not close enough to any high pressure areas where it could blow out. leave well enough alone.

 

We are moving forward!!! I dropped of the heads with "City Motor Supply" here in Dallas. It took some coaxing to convince them to take them. I had all of the parts labeled and provided them with these images for re-assembly. That gave them the confidence they needed. We ordered the teflon valve stem seals D1610 they came in packs of 16 so we just ordered two boxes. It feels really good to see movement again. I took some time to take care of a side project.

 

Got a call from the shop. They need to replace 5 exhaust valves and my input on how much to fly cut. I thought it was a strange request on the exhaust valves. Any thoughts?? I found a gentleman here in DFW that parts out XJS and was able to buy a rather roughly treated head (pried loose and studs cut with a sawzall) that I hope has acceptable valves in it. He even thought that the requirement of the valves was odd.

I Purchased my tube of Loctite 518 for the tappet block to head seal and will visit the shop at lunch today.