Hi all.

What is the science behind the use of different size main bearings on the AJV8 engines?

As I understand it, a code on the block informs the rebuilder what color bearing shells to use and where, and different size shells, as specified by color, are used on each main journal. And, in some cases, different colors top and bottom. Oversized bearings are a thing of the past and thus, the crank can no longer be turned undersized to repair a damaged journal rendering them unrepairable.

I suspect this is driven by the need for increasingly tighter tolerances and allowed by today's computer managed machining processes. Correct? If so, shouldn't that same technology allow the crank and block journals to be be precisely machined without the need for variable size bearing shells?

Maybe I'm wholly off base. Can anyone enlighten me?

Thanks!

 

Select fit is nothing new on bearing inserts, pistons etc. Don't know much about machining tolerances but I guess there is enough to do the select fit technique.

Doug

 

Series I,

Your first paragraph is just about spot on. The same selective process is used during original build and subsequent replacement.

My non-engineering perspective:

Higher MPG and thermalefficiency is achieved by reduced internalfriction,achieved by usinglower viscosity oil.

Lower viscosity oil requiresreduced bearing clearances to maintainrequired pressure.

Standarizing machining tolerances downto .0001" increments during the mass production of crankshafts, cylinder block and connecting rods is a difficult task to achieve and maintainon a consistant basis.

So the tooling gets it close, and the bearing selection gets it perfect.

Doug is quite right, I remember seeing this for the first time on a Honda car engine in 1978.As you noted, it brings more complexity to enginerebuilding.

 

Thanks for the info guys!

 

It is very simple. Blocks and cranks are mass produced and it is a lot cheaper to make 20 different bearings and piston sizes than it is to produce blocks and cranks to exacting tolerances. Just measur what you have after production and insert matching pistons and bearings. Remanufactured engines can have their cranks cut and blocks line honed or bored and bearings are available. It's much more labor intensive this way and that's the only reason production engines use the multi sized parts.

 

main bearing clearance is 2 tho and rod journals are 1-2 tho

 

Is that right. Tell me where I can buy oversize bearings for AJ26/ 27 and I'm all over it.

The factory only sells new cranks, with bearings to suit. How they select the shells tosuit a particular block in this case is something I don't know, nobody has given me $1000 to buy them a new crank yet.Jaguar doesn'tlist anything beyond the standard selective range for original sized crank journals, and I haven't found them in the aftermarket either. Nor do I expect to.

The selective coding system makesthingsalot easier than buying apair of mics andbore gaugesaccurate enoughto do .0001" measurement.I fit good used cranks to good blocks by combining the appropriatecodes and recharting the correct bearings, no problem.

The greatest benefit of this system is that the main journal bores in the block are being measured after original machining, which wasn't the case back in the day. I rebuilt dozens of SIII 4.2 Lengines which were incorrectly sized at the rear main saddle, andcooked the rope seals while they were burning up the rear mainbearing shells and cranks. Many were still under warranty, and paid a total oflike 16 hours for R&R and full rebuild. At least then you could cut a crank .020" and have the main saddles resized. Beats paying a dealer $11,000. to install a rebuilt engine when you spin a rod bearing on an AJV8.

 

AJV8 rebuilding is certainly not my speciality but I have run across a lot of information on the internet regarding pistons, cranks and rods as being available from someone. I've even read about a twin turbo AJ27? running aluminum rods , resized crank and custom turbo pistons on methanol. Obviously probably not a standard rebuild situation but anything is possible if you no where to look. I know a lot of hot rodders that have bearings, pistons etc. made at costs low enough considering the potential value of a properly rebuilt AJ engine to be feasible. I've yet to see a properly rebuilt engine from anyone other than Jaguar. I even had one that was supposed to be a complete rebuild that had 4 used plugs on 1 bank and 4 new plugs on the other plus the presence of sand on top of the block warranted further inspection. When the plugs were pulled the piston tops all had extensive carbon buildup and sand blast sand on top of the pistons!?!?! A call to the rebuilder was answered "It will be fine". After adding the parts that come on the Jaguar rebuild the customer saved a whopping $300. The engine had VVT faults from the minute it was started and was towed from Detroit to Kalamazoo(the rebuilder) so the rebuilder could fix it as they didn't want to pay us to fix the problem.

A little rambling but you get the picture.

 

Yeah well, I have searched for oversize bearings before, I was looking for a little specificity.

Speaking of which, was that Autosports Unlimited who built the honkmotor?

If a customer purchased a rebuilt orupdated used engine, as mine have, they wouldn't likely be going to a dealer for service. That might be one you saw, and they were looking forsubstantiation that they were sold junk.You won't be seeing any of mine.

 

Let's see if this works

[IMG]local://upfiles/3394/7F08A0E62209451D9E2B4E9DA1B80D3E.jpg[/IMG]

[IMG]local://upfiles/3394/268F854A895B4637B699DFDBAB1CD4AB.jpg[/IMG]

[IMG]local://upfiles/3394/35B991721B0842918A5258C13354828C.jpg[/IMG]


There we go. Sorry, no sand or used spark plugs available. You get the picture.

 

Im re building a aj26 engine . Its new im actually converting to supercharged . Cuz i just a xjr .im gonna install new bearing on monday when they come in . I cudnt find anything on aftermarket bearing as well as main bearings.found some piston rings thats about it

 

Cool, and nice to see you back on here, by the way. Did you come up with a good set of used S/C pistons?

One other thought, in case you haven't come across it yet: the AJ27 oil pump is higher output, as required for the CVVT's. It's a direct fit on the AJ26, in fact the early part number supercedes to the later pump. So unless you're already planning on a new oil pump, you will get a benefit by using a good AJ27 pump instead.

I have a couple of scattered AJ26 and 27 engines for parts, if you get hung up for anything and a used component is acceptable, get in touch. Your sources for new stuff is at least as good as mine.

 

One other thought, in case you might not have run across it: if you're using heads from an N/A engine, you'll have to plug the VVT oil gallery ports. There is an old bulletin about removing the plugs on new heads for use on N/A engines, so that will show you what I'm talking about...in reverse.

 

Go here http://www.lincolnvscadillac.com/showthread.php?t=36831to read about the Jag AJ engine build for the TT land speed Lincoln LS. When I first came across this engine project a while ago I thought it was a done deal and parts(bearings, pistons etc.) would be available. But the latest post is dated 2 days ago and it is not complete. It's a great read and the time and expense spent as the first to try this should pay off for the rest of us interested in lowered parts cost and availability of custom parts at lower than first adopter pricing. Time will tell and I know I will be watching the progress as the builder is local to me.

 

I just wasted a bunch of time reading through your reference material, which has nothing to do with the questions I asked you. What I did read was the following excerpt enteredby the guy writing the log last November:

"We did some measuring today and found several things. First, on very close examination, the main cap/girdle has steel inserts cast into it. In other words, each 'cap' is actually steel, with the steel being an integral part of the massive aluminium casting that bolts down to the underside of the block".

What he is describing there is the stockengine bedplate, and of course it has steel reinforcements, which are obvious the first time you hold one in your hands. So he writes about it like it's some grand technical exercise to decypher and quantify the significance of this discovery. I don't care how much of the rest is bullshit, that passage is and so is there bound to be more tossed around in that log.

The shop that does my machine work builds hi po rods and blower drives in-house, anything else can be custom manufactured, that's no news. We had custom cranks made for the race-winning Triumph TR4 I wrenched on, they cost $1500 each in 1977 dollars. Every word ofmy paragraph is completely irrelevant to the subject of rebuilding engines for Jaguar passenger cars, which I think was the original point of this thread.

Where do I buy oversize crankshaft main and connecting rod bearings, without commissioning a production run?

Who built the honk engine that you claim had to be towed out of your dealership?

And since you've "yet to see a properly rebuilt engine from anyone other than Jaguar", can you provide a statistical approximate of how many improper ones you have seen? Like one? If more than one, and if supplied by more than one builder, I'd like their name as well. I should think that any owner with an XJ8/R, XK8/R, or 4.0 S Typewho is stuck with a failed engine would want to know the names of negligent suppliers.

I haven't seen any of Motorcar's rebuilt engines, I suspect they are "properly" prepared and quite satisfactory for the intended purpose. So are the engines that leave my shop.

 

Jto- thanks . I m using the old pistons in my old xjr engine. Ive checked the parts catalogue maybe ill double check again . I found the part numbers where the same for n/a and sc. Heads . Ill check for the bulletin i doubt it will still be on our jag website . Ill look around

 

_genius,

Yeah the heads are the same, I'll PM you the bulletin number about the V V T gallery plugs later. It was fromlike '98, butmy shop puter isn't online so I can't forward it.

 

@jag-genius
The bulletin was 303 – 31, Here is some of the text:
· Cylinder heads are supplied by Jaguar Parts Operations as common units for all three variants of V8 engine, i.e. 3.2 Litre, 4.0 Litre normally aspirated and 4.0 Litre supercharged.[/i]
· The oil supply gallery for the Variable Valve Timing (V.V.T.) unit is present on all of these cylinder heads, whether a V.V.T. unit is fitted or not.[/i]
· As supplied by Jaguar Parts Operations this gallery is blocked by a blind rivet plug, and is hence to Non-V.V.T. specification.[/i]
· When a replacement cylinder head is to be fitted to an engine which is equipped with V.V.T. units then that cylinder head must have the blind rivet plug removed before it is fitted to the engine, otherwise V.V.T. will not function on the cylinder bank concerned.[/i]
· The aluminium blind rivet plug in the V.V.T. supply gallery is secured in position in a similar manner to a pop rivet in that the centre pin and cone is pulled to expand the rivet until the pin shears below the head. This leaves the aluminium plug and the head of the pin in position to seal the gallery[/i]
·The Cylinder Heads listed above can be fitted to all variants of the V8 engine, i.e. 3.2L, 4.0L & 4.0L s/c, 1997 MY or 1998 MY. This information is NOT applicable to 1999 MY vehicles.[/i]

As the compression ratio is going to be bigger with the NA pistons, you need to be extra careful with the target boost level. I am not sure if the stock 11.6 psi pressure (if that was your plan) of a stock SC engine would be safe. Also think about the strength of the pistons, as I thought that the SC ones where a bit stronger and better to double check if there is enough valve clearance with the SC cams and NA pistons.

Andre.

 

Greetings Andre,

Nice to hear from you, and thank you for saving _genius and myself a little work. If I understand him correctly, he's using S/C pistons so I think he has that covered. When I read his first post I had the same concerns, but I'm glad you describedthe differences clearly for us all.

 

i found it at work i drilled out the vvt holes enlarging them and installed and loctite a set screw on both heads. Worked perfectly . thanks. And yes im using the sc pistons andre. Dint have alot of time i just did the heads and check the clearance of the crank journals with plastiguage.just have to install the new rod bearings and check there clearances as well.