3.4 litre engine upgrades?

Question mark because I’m seeking advice from the much more knowledgeable in this here XK forum.

I’ve torn apart my ‘54 XK120 engine and am putting together a list of replacement parts for the rebuild, pondering extent.

The engine is in remarkably good condition, having been run only 20K miles before being parked in 1966 and kept in various dry storage conditions since. It has not been run in all that time. I’m being advised by a mechanical engineer friend with extensive engine rebuilding experience that the cylinder walls need only a hone and the crank and cam journals a light polishing. Timing gear no discernible wear either. All the engine really needs are new gaskets and seals, though replacing the cam and crank bearing shells and the rings are no-brainers.

But what would be advisable otherwise?

The lower chain tensioner is fully functional but definitely primitive - is there a more modern replacement? Ditto the front crank seal. Any advantage to lighter weight, modern pistons, like Mahles? Stick to 8:1 or go to 9? Higher volume oil pump? New valve guides with seals? Other?

This will be a lightly used street machine, maybe a thousand miles or so a year. Looking for reliability more than anything, though a little boost in performance above the SE specs wouldn’t be unwelcome.

What say you, ye wiser ones?

If you trust the person who gave you that advice, I would go with it. There is something about driving a 50 or 60-yr-old vehicle about with as many of its original components as possible, in my opinion. Why change original parts for more modern alternatives? At what point does the car cease to be a '54 XK? I know that’s an extreme view, but the old car world is heading towards being an important part of history rather than being regular transport. For that reason alone, keeping as original as possible is a good idea… and let’s face it, whatever you do to it you won’t be able to keep up with well-driven modern hatchbacks. The dynamics just ain’t there.

You may get a lot of opinions. Here is the low-budget opinion. :grin:
Rings and rod bearings and gasket set.
I have found that cam bearing wear is often minimal even at high mileage.
Main bearing wear also not expected at 20,000 miles.
The front crank rope seal works if you install it right.
There is no alternate oil pump.
There is no alternate lower chain tensioner. Check for wear on the end hooks of the spring. Mine broke once, but it has high mileage.
Valve stem seals don’t seem to be needed. Mine doesn’t have them and doesn’t burn oil.
Its more dependent on any rust that developed in 55 idle years.

I stayed with the original oil pump and chain tensioner. Like Roger said I wanted the xk 120 period experience. However there are mods that allow the later type oil pump and chain tensioners to be used) when I looked at these I was not impressed with the quality.
As Rob listed bearings etc are a no brainer. I would also keep the original pistons if they look ok.

1 Like

FWIW, I’d keep it as stock as possible, with the exception of an ignition system, like a Pertronics dizzy: that is the least expensive and most-meaningful update you could do.

Thanks, gents. The main bearing shells do show very little wear but a new set is pretty cheap, like a hundred bucks - plus I have a few shells separated from their caps and don’t imagine mixing their original positions around would be a good idea.

1 Like

I replaced the pistons with Mahles when I did my E-type 4.2 rebuild because the ring grooves were over spec. Not the case here. Nice thing about them was they’re plug and play. Supplemental question. Are replacement ring sets pre-gapped, like those installed on replacement piston sets, or is adding a ring grinder to my list in order?

Never assume, always check a ring for proper clearance, and if you have a fine grinding wheel, ring gaps can be set on it.

Shells should always be replaced, due their crush having been…crushed.

Good advice - though I think camshaft shells are the exception.

Correct: they are under so-little stress, I reused them all the time.

Put the best ones in the front two positions: they get the most worn, and tightening the chain can result in too-tight clearances on the #6 valves.

What are your thoughts on the newer XJ6 connecting rod / big end bolts and lock nuts, eliminating the original castellated nuts and split pins? (What I installed in my 4.2).

Can’t hurt!

You can use modern bolts and nut in the 3.4 rods. If you aren’t planning to spend a lot of time above 4500 rpm, I’d wager the stock rods are adequate.

Nick, on ring sets: I had a set of std. size AE piston & rings, installed into a bore with 30k miles on my 4.2. The piston skirt clearance was .00275". The ring end gap was laughable. As I recall .030" +/-. Loose rings are better than too tight…if you’re a piston manufacturer I guess. Total Seal sold me some nice cast iron rings. Tight lands and adequate back clearance, I gapped them at .016".

How about a nice three angle valve job for improved performance?

This is what I’ve done with mine, a late '50 '120:

  1. Block core plugs are brass. Dorman no longer makes them but my local auto parts was still able to source them.

  2. Cylinder head tappet guide hold-down kit – exhaust side. Doing it for the inlet side would be a waste of money as it already runs cool enough. I also had my rebuilder install oil seals for the valve stems since, as it was already apart anyway, why not? Adds almost nothing to the final cost. I’m aware that they’ll lose effectiveness after some 50k miles.

  3. My radiator guy upgraded the core to 4 rows from the original 3. All of the external dimensions are still the same. Probably not necessary where you are but Northern California is subject to temperature extremes.

  4. Blank off where the Otter switch would have gone and install a switch somewhere discreet under the dash. The less time gasoline is washing lubricant off your cylinder walls during engine warm-up, the better.

  5. Panty hose in the upper radiator hose. I cut part of the foot off of a pair of Jan’s hose and use that to catch any detritus in the block from fouling the core tubes of my rebuilt radiator. This will come out after a few thousand miles.

  6. Delrin/ acetal throttle shaft bushings in the carbs. Sounds like your low mileage engine doesn’t need it but if shaft slop here is exceeding 0.005" then you might have idle speed issues. Also brass on brass for a bearing surface isn’t the best when there are now better alternatives.

  7. Sealed-for-life ball bearings in the generator.

  8. That lower timing chain tensioner mount/ spray oiler? It looked flimsy so I made a duplicate of steel instead of the thin cast aluminum.

  9. On the lathe I profiled the V’s of all pulleys so they accept a commonly sourced B36 belt that sits uniformly flush with the top edges of the pulleys. The lower engine pulley I fabricated using the old one as a model.

  10. ARP connecting rod bolts/ nuts. I was on the fence in my decision over this one for some time and still wonder if that might have been overkill as this car won’t get much more than some spirited driving in the local mountains.

Everything else about the engine was kept stock. Others may applaud me on some points and shoot me down on others, but this seems to be working for me so far.


All sound like reasonable mods, to me.

Thank you sir. I got most of these ideas from you guys.

Referencing minimum attention to refresh the engine as described, what about desludging the crank?

Takes some effort to remove and replace those sludge plugs.

our Club guys tend towards the view this step cannot be skipped

I would assume that situation would be amplified if the engine was unused for a long period of time, as it would give the sludge more of a chance to solidify

we have a local Jaguar specialist who also has a machine shop and builds many high-performance engines, he does them

They used Mahle pistons in my engine rebuild. They are a 4 ring design with one ring below the gudgeon pin. This provides extra stability and piston rock in the bore resulting in less noise, I was told. This is a street engine, of course.

Don’t skip this step:: PITA, but usually needed.