Hello everyone, is it possible ? Are 4.2 l engine blocks compatible between the 3 series? I need to rebuild a series 1 engine with a damaged block. Idea is to use a block from an other engine rather than restaure as the original block is pitted and damaged. Thank you in advance for your kind help!

 

Yes, that should be no problem.

 

I am not so sure! I thought that later blocks had repositioned cylinder spacings! Or am I mistaken? Alec G.

 

The spacings changed from the 3.4/3.8 to the 4.2, but all 4.2 have the same bore spacing. There were 2 extra cooling passages added to the back of the block in 1968, but that won't matter between Series 1 and Series 3 XJ.

 

Thank you for your response, so it looks like I’ll have lots of options for parts of all 3 series are compatible block wise. Any one knows what evolutions/improvements were made over the years? Is it always bear in the cylinders or are some later blocks steel lined?

 

All of the XK engines from 1948-92 have steel sleeves in an iron block. If your existing block is oversize an option is to press out the sleeves and install new ones to bring it back to a standard bore size.

Some of the engines had problems with the block cracking between the bores, so examine that closely - ideally have a machine shop use a specialized magnetic particle detection system to see if there are cracks. Some of the later blocks were slotted between the bores to help prevent cracking.

Series 3 heads have larger valves than the other engines, so in theory should have slightly better breathing. I doubt you'd notice a difference in the real world.

I think from about 1982 (?) the crankshafts had a special hardening and cannot be reground. They generally don't need it though.

A good history of the engine and it's changes over the years is written by Roger Bywater, a former engineer at Jaguar, 6 parts starting here: http://www.jagweb.com/aj6eng/xk-engine/

 

Interesting thank you 🙏 I never had to learn about these engines before as since I own the car it caused me no troubles. So: if given a choice a series 3 engine is better

 

Yes, but only if it's not cracked. I wouldn't necessarily seek out a Series 3 specifically, but if you can find one cheap, go for it.

 

That’s the plan!!!! :-) if I had the funds I’d have it rebuilt for the 14k figure I see on specialists price lists. But I need to be smart otherwise that poor car won’t see the road back anytime soon

 

14,000?? Euros? That's a crazy number, it shouldn't cost anywhere near that much. That being said I'm not familiar with machine shop prices in Europe, but that's a lot of money. An option might be to get a "good running" engine from the UK and drop it in?

 

Yes it’s prohibitively expensive… and pretty much all are in line give it take 2k. There are plenty of used XK engines out there. I just need to gather sufficient knowledge to select the right one

 

I've put a S3 engine in a S1

One snag was the S1 have round openings at the back of the cams, and S3's do not.

On a S1, the openings are plugged with a round seal, and their mounting bolts also serve to hold the throttle linkage.

S3's have fuel injection, and the cam covers are flat, so they were not drilled and tapped for the round seal, which means you don't have a way to hold the throttle linkage.

Once installed, there's no room to drill and tap, but if you do it before installation, you will be okay.

Rob

 

That would only be a concern if the S3 head was used. If we are only talking a short block then it's easy to swap heads.

 

Thank you so much, it’s very informative!! In this case I’ll keep my original head. As far as we know only the block is damaged. We haven’t dismantled yet but our guess is head is fine

 

The later "slotted block" engines do not have liners. With this version it is crucial to use a high quality head gasket as the lands between the bores and the slots are very small.

 

Can you identify these slottered blocks on the outside? Are they better than the earlier ones?

 

Not true. The original 2.4, and 3.4 engines were not sleeved, but the 3.8 litre was sleeved due to the casting getting a bit thin due to the boring out, (or so Jaguar thought at the time). The 4.2 litre engines with their siamesed bores were sleeved because Jaguar machined coolant cross-passages via the bores, then covered them with liners. This then set off the block cracking problem that I suffered from. Worst were the 7L and 8L engines, although I was fortunate to find an uncracked 7L block to replace my 8L one on my 1980 XJ6. From about '82 or '83, the slotted blocks came in with no liners, but slots between the bores. This cured the cracking problem, but then led to the head gaskets only lasting about 80k miles. Of course today, with most cars not being daily drivers, this interval is OK, you just have to be aware of it as a possibility. Whether one can know whether the block is slotted from the engine number, I'm not sure.

 

I learned something! I thought they were all sleeved. We never got the smaller engines in Canada, so I have never had one apart.

 

I’m glad I started this topic! So each of the two versions has its issues. Cracking or head gasket failure. Im guessing todays high quality gaskets must be better than the ones made in the 80s. So the way to go would be a block from 83 onwards fitted with my original S1 head and reassembled with a top quality gasket set after a re machining of the surface to ensure a perfect mount.

 

The Cometic MLS gaskets are excellent. They are also available in different thicknesses to compensate for the metal than gets removed in surfacing the top of the block and the head. This prevents the compression ration from getting to high and causing detonation.