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3.4 is 83mm bore, 3.8 87mm bore... stroke is the same 106 mm.
It's 83.7 mm, it's been bored, so it's a 3.4. I was hoping it was a 3.8. The owner said it was a 3.8.
So is this engine still a better choice over the 1973 4.2?
The 3.4 is a far more rugged engine and will cop lots of abuse. Unless you are trying to be super competitive, I'd use this engine.
The 4.2 engine has problems like corrosion on the head hold down studs which are in the block's water jacket and seems more prone to block warping and cracking between cylinders.
Actually the 4.2 XK engine was "stretched" a little too far in my opinion.
It's 83.7 mm, it's been bored, so it's a 3.4. I was hoping it was a 3.8. The owner said it was a 3.8.
So is this engine still a better choice over the 1973 4.2?
Is this an 8:1 or 9:1 piston? That is an 8:1 piston ~ what's in my car.
Pistons.
Last edited by Glyn M Ruck; Mar 17, 2024 at 07:14 PM.
The 3.4 is a far more rugged engine and will cop lots of abuse. Unless you are trying to be super competitive, I'd use this engine.
The 4.2 engine has problems like corrosion on the head hold down studs which are in the block's water jacket and seems more prone to block warping and cracking between cylinders.
Actually the 4.2 XK engine was "stretched" a little too far in my opinion.
The 3.8 with it's Brivadium sleeves from Bristol Aircraft will take the most abuse. The 4.2 with their block cracking are a bit of a disaster. This article was originally written by a Brit ~ this is condensed. Fraser Mitchel claims approx 80% crack.
The 3.4's were more than adequate prior to the UK's motorways. Thereafter many police vehicles were up powered to 3.8. There is only 10 bhp difference between the 3.4 & 3.8 with B head. But this does not reflect the full story. The torque characteristics between the 3.4 & 3.8 make a substantial difference. Even some 340's were fitted with 3.8 engines but not that many due to it being a run out model for the XJ6 along with all the other compacts.
I can understand the enthusiasm for the 3.8 engine. I have had a couple in MK2s and a "hot rod" MK1 which was converted from a 3.4 auto to 3.8 MOD with disc brakes all round.
However, it is my understanding that the only choices for jayd2 were the 3.4 or the 4.2. He mentioned he was on a budget.
I have had a lot of experience with both engines and for simplicity and reliability I will take the 3.4 any day.
My son and I have had 4 XJ6 4.2 cars and my previous remarks on the engine were based on experience.
(I still have one series 3 XJ6 4.2.)
So be it. South Africa thinks differently. I would certainly take a 3.4 over a 4.2. We built 3.8's to 3.4's on a ratio that vastly favours the 3.8. ~ All S Types built here were 3.8s. We have power sapping altitude to deal with in the hinterland/highveld.
Last edited by Glyn M Ruck; Mar 18, 2024 at 09:58 AM.
Roy James, aka 'the weasel,' favoured the 3.4 for leaving the scene of the crime as quickly as possible. The 3.4 has a certain pedigree having won Le Mans three times; the 3.8 only once and, even then, the next three cars behind it were all 3.4 litres. Jayd's vintage racer doesn't look like a heavyweight so the difference in torque isn't a great consequence. My suspicion is that a 3.4 with a 3.77 axle does close to everything a 3.8 can driving a 3.54 and will be happier (or less unhappy) when you reach the red line.
;.... My suspicion is that a 3.4 with a 3.77 axle does close to everything a 3.8 can driving a 3.54 and will be happier (or less unhappy) when you reach the red line.
Jay
This should definitely be considered in final outcome. A poor choice in rear-end ratio (limited slip - or not), could upset all of the work ahead of it for drivability. Engine, tuned for low or high end torque; 4 speed plus over drive, in a light weight vehicle??? This can all be done on paper (really cost effective) with all the experts in the world adding their actual experience.
Rgds
David
I know the PO thought it was a 3.8 from 1959. If it was 1959, my guess it would be from Mark I or II
The 3.4-litre XK was used in the following road cars: with a bore x stroke of 83 mm × 106 mm (3.27 in × 4.17 in) 3,441 cc displacement . It had an iron block without cylinder liners and aluminium cylinder head. It had a wider gap between cylinders 3 and 4 than between the other cylinders.
A small point, David, but the first 340 cars sold in North America had B type heads. I think they came out of the production line as regular LHD 3.4 Mk2 cars and were subsequently modified, mainly re-badged. The cars that were built as 340s had straight port heads. I think the 'converted' cars had Mk2 chassis numbers while the 'built as' had their own series of chassis numbers 1J..... .
If it were me, I'd stick with the 3.4 engine, the original size from 1948. The 3.8 engine needed liners, because boring out the cylinder size on the block, which remained unchanged, cause the remaining metal around the bores to get a bit too thin in places.
The 4.2 litre engine was a stretch too far, and the 7L and 8L blocks with their long studs, were pretty much a disaster after a few years use, because they suffered cracks between the bores that caused endless head hasket failures, (like on my 1980 XJ6 !!!). I was lucky to get hold of an uncracked 7L block to replace my cracked 8L block. The cure for this cracking is to fit "top-hat liners" that replace the existing ones, the lips of the liners covering the cracks. Have look here at what is involved, it isn't a cheap job ! Jim's Automotive Machine Shop, Inc. - YouTube
You can see the reason for the cracks when the block without its liners is shown being measured. The slots in the cylinders were machined to provide cross-block water passages, and then covered with liners. The cracks occur between the block face and the first water cutaway.
Last edited by Fraser Mitchell; Mar 18, 2024 at 05:05 PM.
I had two issues while disassembling the SU HD6 carburetors. The banjo bolt on the front carb float chamber was seized to the threaded stud. The tip of the stud snapped off. I've drilled out the stud in the banjo bolt, now I need a tap to chase the threads. I welded a 0.25 rod to the tip of the float chamber stud and now I need the proper die to thread it. The stud measures 0.25, is that a 1/4"-26 BSF thread?
One of the four float chamber mounting screws was seized also, it was rusted the full length of the screw shoulder. I had to drill out the shoulder section of the screw, the treaded piece came out easy, carb body threads are good. I need a replacement screw, is the one in the photo the correct one? It looks correct, what size thread is the screw?
[QUOTE=jayd2;2732196]I had two issues while disassembling the SU HD6 carburetors. The banjo bolt on the front carb float chamber was seized to the threaded stud. The tip of the stud snapped off. I've drilled out the stud in the banjo bolt, now I need a tap to chase the threads. I welded a 0.25 rod to the tip of the float chamber stud and now I need the proper die to thread it. The stud measures 0.25, is that a 1/4"-26 BSF thread?
One of the four float chamber mounting screws was seized also, it was rusted the full length of the screw shoulder. I had to drill out the shoulder section of the screw, the treaded piece came out easy, carb body threads are good. I need a replacement screw, is the one in the photo the correct one? It looks correct, what size thread is the screw?
Be sure to keep the two carbs separate when disassembling. When you get the full list of what needs replacement, check with Joe Curto in New York.
He has everything and is willing to answer questions on rebuilding options and best practices. He has all the parts and used cases if you have too much corrosion on something.
CONTACT
CALL TO ORDER PARTS 718-762-7878 E-mail: JoeCurto@Aol.com
LOCATION
22-09 126th Street
College Point, New York, United States,11356
He did the work on my XKE conversion from OEM 2 ZS to 3 ZS on 420G manifold. Highly recommended.
Rgds
David
Roy James, aka 'the weasel,' favoured the 3.4 for leaving the scene of the crime as quickly as possible. The 3.4 has a certain pedigree having won Le Mans three times; the 3.8 only once and, even then, the next three cars behind it were all 3.4 litres. Jayd's vintage racer doesn't look like a heavyweight so the difference in torque isn't a great consequence. My suspicion is that a 3.4 with a 3.77 axle does close to everything a 3.8 can driving a 3.54 and will be happier (or less unhappy) when you reach the red line.
In that case yes. But in SA it was a matter of Torque, Torque & Torque. The 3.8 was always the favoured engine with it's Brivadium bores. Why every S Type produced here was a 3.8. Not a single 3.4. We are talking about driving on public roads with long distances between towns & our altitude issue. Le Mans is at sea level = 51 metres.
Last edited by Glyn M Ruck; Mar 18, 2024 at 07:44 PM.
These are possibly built mainly for the race engine builder who have the odd conrod poking through the block on a classic 3.8 Mk2 racing car. Can't see Joe public forking out this amount unless they are super rich.
