NOS pistons versus new

My son, Zach, and I are embarking on a restoration of a 1954 XK120 SE OTS. We will be rebuilding the motor and have a Piston question. We have a set of NOS .020 Jahn 8:1 pistons with Grant piston ring circa 1960s. If in the unlikely event the block can be bored to .020 over can/should this piston set be used or should we use a modern set of pistons? Any advice is appreciated. Dave

Nothing wrong with those pistons and rings, at all!

The block–if not badly gouged or damaged–will tolerate a 20-over bore just fine.

Check the bores on the block presently. If already more than 20 over then those pistons will not be useful. If 20 over presently then usefulness will depend on what needs to be done to the cylinders. If the block can come in at 20 over then Paul’s advice is good. You may get lucky.

I believe the bores are currently .010 over, I am unsure whether boring to .020 will be adequate to clean up the cylinders, ovality and cylinder wall scoring. It is my understanding that it can be bored up to .030 over, if that isn’t enough cylinder liners will have to be installed. Please correct me if I am wrong.
If we can get away with .020 over we will use the NOS pistons.

A bore gauge will be called for: who’s doing your machine work, these days?

Hey Paul, Dave Olsen at MileHigh Crankshafts has been doing our crank work for the past 15 years. Area Machine Shop has been doing our machine work. They are located at 64th and Federal, Rick is the owner and knew your family. Problem is independent machine shops are closing and the survivors are buried with work. Area is two months out on block work and six weeks out on heads. They sold the crank equipment because they couldn’t keep up.

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The other option is relining them and then boring to use your pistons. It adds to the cost certainly but it gives the luxury of being able to thoroughly clean the water jacket slots. Mine were completely closed off.

Yea: I began using Olsen for crank work 30 years ago… but block stuff, I lost that lead when Randy S. went south on us.

If you decide to restore the liners with new, make DAMN sure you use ones recommended by the likes of @Dick_Maury, and I can show ya the neat trick of using MIG welding to drop out the old ones!

Turns out the old pistons are standard as indicated by a “G” and on the piston and a stamped “G” on the top of the block next to each cylinder. Bore gauge coming tomorrow so I will be able to check for ovality, taper, and wear.
Stay tuned.

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I have Jahns pistons in my XK120. They seem to be still in business, now known as JE Pistons in Cypress CA, and though they do not list Jaguar in their standard product line, they offer custom pistons for Jaguar.

Good to know they’re still extant: I wasn’t sure.

Paul can you please elaborate on using mig to remove cylinder liners?

I can help there, running a bead of weld around the bore (can be MIG or stick) creates a shrinking effect as the weld cools, this reduces the interference fit of the liners.

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What Robin said: done properly, the liners will almost fall out of an upside-down block.

Paul thank you for the heads up about the 60 spoke wires.
Okay secondly, I know I am a novice with these motors and as my forum name implies I remain the Confused One, my question is did these motors come from the factory with liners? I can’t find anywhere in the original manual that says the cylinders were originally lined. In addition there is no apparent seam on the block. Thanks for the clarification.

Thanks guys. I guess the devil is in the detail as to ‘done properly’ ?
Are you saying one circumferential weld as far down the bore as possible? Or a longitudinal weld as far as can be done from both ends?
I’m only asking as I need to remove one/all the liners from a series 3 xj6 engine. The quotes from machine shops are very expensive!
Best regards

  1. no the bores were machined directly into the blocks from new
  2. I would go with circumferential welds possibly in 2-3 places top middle and bottom.
    Wiggs, whats your thoughts?
  1. I simply had forgotten–if I ever knew–if 120s had sleeves.

  2. not an option, for Dave, but I always used 3 straight welds, top to bottom, turn the block over, and then let’em fall out. Another Dad tip!

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The V-12s have liners, in case there is any confusion and you hear of Jags with liners. I don’t believe any XK engines had liners.

Kinda picking the fly poop out of the pepper…:smirk:

To be completely accurate, the V12 (and TR2/3/4 engines) have wet liners.