M20 Engine Info and advice

[cabrioman]

Hi All

I am considering changing the engine in my Marlin Hunter (think cabrio) to an M20 2.5, which I know many on here have used.

Is there any significant differences and advantages between the early or late engines. I know the injection changed from jetronic to motronic which I believe was to allow closed lambada control with a CAT but should I be looking for one in favor of the other.

The car was registered in 97 as new (factory built) and has been running a ford engine with cat which met 97 emission regs. I will need to prove the age of the new engine at MOT so emissions are tested as per the engine I use.

Regardless of the year of the M20 I can't see any emission issues at MOT providing I can prove engine age.

Makes me wonder if the earlier engine is the better bet to avoid having to use a cat, but do I lose out there with an inferior early injection system or are there other differences between the early/late engine which would/should influence the choice.

Sorry for the ramble, any info gratefully received.

John

[GreatOldOne]

Hi John,

I don't think any of us with M20's have cats, as all of our engines are pre '93, when the regs came in.

My M20 2.5 came from an '86 car, but it seems it was a transitional engine - not a lot different to the later engines (different main bearing shells, a "D" shaped diagnostic plug on the engine loom rather than the circular one of later cars, slightly different cooling plumbing)

It runs Motronic 1.3, and does not have a catalytic converter. I believe all the other guys are also running Motronic.

I was able to prove the age of the engine at IVA as I still had the Donor V5. I would imagine you'd have to get the date of manufacture of the engine from BMW, so you could present that to DVLA / VOSA so your log book could be changed.

You might have to go for a VIC at a VOSA station... I'm not sure on that though.

[cabrioman]

Hi GOO

The reason for the comments on CATs is that the BMW info on decoding the block engine code shows "k" as standing for CAT and I have already been offered an engine which came out of a J reg 325 which had the code 256 K 1A which denotes 2500, 6 cyl, Cat, with 1A being a version number relating to line and new or remanufacture.

I must admit I was surprised that an engine that old was CAT so maybe the blocks were used at the time in countries which had tighter emissions.

With the comments you make about your engine being transitional it may make better sense to obtain everything needed from one source vehicle to ensure it all matches.

Don't think it will need VIC, I know BMW will supply a letter stating date of manufacture based on the engine number. MOT emissions are based on engine or vehicle age which ever is the oldest, providing dates can be proved.

John

[GreatOldOne]

Hmm - mine is 25 6E 1 engine, which is high compression...

I say that mine was transitional as that's what the chaps at Motormec called it when I rang up to order the bearings for it during the rebuild. They's slightly different in the way they locate in the block, as they sepecifically asked what shape the old ones where.

I also recall now that my ECU had a different connector on it to everyone else (white, 2 rows of pins), so harvest that with the engine loom.

The plumbing difference is minor - all the other chaps had a metal water pipe / channel that ran diagonally across the front of the block, bolted to the timing case. Mine didn't, and didn't have any mounting points for one on the engine. I just had different rubber hoses to make up for it.

Not that it mattered as they all got chopped up top fit in the Sportster anyway!

[MartinClan]

My donor was a G reg - and it had a cat and (still has) a Lambda sensor. It was an import from Switzerland. It doesn't have a cat any more but when it was SVA'd the tester remarked on how low the emmisions were...

Robin

[peterux]

Mine is a 2 litre from a 1989 F reg car, no CAT (but the loom had the connectors for lambda sensors), Motronic injection and no problem with emmissions at MOT's.
...peter

[peterux]

John,
I assume you have seen Simon Gregory's car and Flickr photo site?

It's an M20 in a Cabrio...

http://www.flickr.com/photos/marlin_bmw_cabrio/

regrds

Peter

[Sorton]

All very interesting, my F reg (1 Jan 89) 325i Sport donor was always described as "cat prepared" or "cat ready" when I went looking for exhausts. It does not have a cat or lambda sensor, but I think it would have done if sold in other EU countries as we were late adopting the cat principle.

This leads me to wonder if it is the lower compression engine.

So I thought I would check to see the engine number and codes but I have totally failed to find them on the block which is still awaiting refurb in the garage. I thought they should be on a machined area low down on the inlet side but can find no trace of any digits - I hope they have not corroded away! Can someone tell me exactly where these markings should be on a UK engine? Help!

[GreatOldOne]

They are stamped into the block just below and to the left of the dip tube. You can just see the flat portion of the block where it's stamped here:



To the right of the alternator mount / bracket, directly under the cap for the oil pump drive (circular silver item clamped to the block), just above the sump line.

[MartinClan]

The engine number is on the left side of the block, low down on a machined surface about 1/3 of the way back from the front. (As I remember). The number on mine was not stamped very deeply - it needed a good clean and a bright light to see it clearly. I rubbed some white paint into it so that it was easier to see for the vehicle inspection.

Robin

[Chris Cussen]

I'm no expert on BMW engines, but my guess is that if you change the engine then all you need to do is inform DVLA of the new engine number (and provide them with a letter from a garage or workshop to say it has been fitted in a satisfactory manner).

DVLA don't ask the age of the engine, so by inference the MOT emissions tests will be unchanged.

[cabrioman]

Chris

I am sure your right but in my case it would be essential to have the MOT based on the engine not my V5 as otherwise the circa 86-90 M20 engine will have to meet 1997 (car reg date) emmision regs which it wont do, certainly not without a CAT.

To all

On another note I have discovered from conversation with the Marlin club BMW technical rep that the changes to the bulhead other cabrio owners have made to fit the M20 into the engine bay are only needed if the anti roll bar is retained. Marlin remove the centre ARB section and mount the engine further forward. Does any one have experience in practical terms of how the car handles without the roll bar intact, body roll etc.. I wouldn't go the Marlin route but I could use compression struts mounted onto the ARB mounts.

Interested to know if this works to save me cutting and rewelding the bulkhead.

John

[Patrick]

Having done an engine swap in a tin top I can report all you need to do is send off the v5c with the new engine number to the DVLA. Nothing else is needed.

For MOT the emissions are always based on the oldest part - chassis or engine. BMW can provide a report on the engines age if required. You can get it here Customer.Information@bmwfin.com I had to provide the donor chassis number and the engine number and the sent me a birth sheet in the post.

Personally I would aim for a motronic engine, something from the late 80's.


Can't comment on the cab but on my sportster I have no roll bar on the front and the E30 325 touring one on the back. A stiffer rear end would lead to more of an oversteer tendency. I've not had the Sportster on it's handling limits so I've not found it a problem. The mechanical grip has been fine for all normal road driving. (a little power oversteer at low speed is easy to coax out of it with a dab of throttle and less precise clutch movement )

[cabrioman]

Hi Patrick

When you say "prove" the donor chassis and engine number what did they require as proof.

John

[Patrick]

Sorry auto correct typo meant "provide"

[Mike]

To all

On another note I have discovered from conversation with the Marlin club BMW technical rep that the changes to the bulhead other cabrio owners have made to fit the M20 into the engine bay are only needed if the anti roll bar is retained. Marlin remove the centre ARB section and mount the engine further forward. Does any one have experience in practical terms of how the car handles without the roll bar intact, body roll etc.. I wouldn't go the Marlin route but I could use compression struts mounted onto the ARB mounts.

Interested to know if this works to save me cutting and rewelding the bulkhead.

John

Ford Sierras have different shaped front anti roll bars.
I can not speak for the M20, but I had a problem with my M50 until I found a different shaped ARB. Have a look on my flickr site (there is a Set marked ARB) and you can easily see the difference. May be Peter Morris, will be able to tell you whether this would make any difference to modifying the bulk head when using an M20?
I know Simon fitted special adjustable rose jointed Track contol support arms and did away with the original ARB and is very happy with the suspension: this has the advantage of making the castor much easier to adjust.

The ARB I have now fitted came from an early Mk1 Sierra, but also appeared on the P100 pick up.
Rgds
Mike

[Patrick]

Did I read that right? The ARB is split into two pieces? If that's the case it no longer functions as an ARB but as a spring.

[Sorton]

Jason, Robin,

Thanks for your responses. Being an engine from an F reg car, the machined section shown on your photo is not there on my engine, however, there is a similar machined section to the rear of the engine mounting bracket. I had already checked this but have now given it a really good clean with a wire brush on my elec drill and a few digits are just showing.

Unfortunately, corrosion has eaten into the surface and old age has had a go at my eyes so more work is needed. White paint will definitely be necessary and I suspect that anyone who needs to check it will need good eyes and a kindly attitude!

Thanks, Sorton

[Mike]

Originally Posted by Patrick

Did I read that right? The ARB is split into two pieces? If that's the case it no longer functions as an ARB but as a spring.

Patrick
Marlin said they would modify my original ARB, so I sent the whole thing off to them, expecting them to shorten the front arms: I received two stub arms back - they had simply chopped the middle section out!(see my fickr )
These arms then act only as tie rods to the track control arms on a Sierra. They do not offer any Anti roll, or even aditional spring tension in one side.

That said it was common for Cosworths to have the ARB removed at the front, and then have special rose jointed tie rods which tightened up the steering considerably.
Simon Gregory has carried out this mod on his Cabrio, and is very happy with the results.
Mike

[Mike]

Originally Posted by Sorton

Jason, Robin,

Thanks for your responses. Being an engine from an F reg car, the machined section shown on your photo is not there on my engine, however, there is a similar machined section to the rear of the engine mounting bracket. I had already checked this but have now given it a really good clean with a wire brush on my elec drill and a few digits are just showing.

Unfortunately, corrosion has eaten into the surface and old age has had a go at my eyes so more work is needed. White paint will definitely be necessary and I suspect that anyone who needs to check it will need good eyes and a kindly attitude!

Thanks, Sorton

Sorton
Do you know the original reg of your donor car? BMW will be able to tell you what the engine number was in that car. It may help with your 'guesswork' of the numbers knowing what the answer should be.
Mike