Engine Mk1 or Mk2

[Dieter H. Marschall]

Hello everybody,

Today I was talking with Stephan Boehm, a renowned German Stag specialist and mechanic.

I had always thought I had a 1971 Mk1 Stag with a Mk2 engine. Stephan thinks I have a late Mk1 engine.

The chassis no. is: LD 1025 BW

The features of the engine are all Mk2: air cleaner housing, inlet manifold,...

According to the Heritage Certificate the engine no. was: LF 10109 HEBW. But now it is: LF 804 ESS.

The lhs. head says: 88313211 and V3293

The rhs. head says: 88313210 and V3294

Both heads have: LM25 WP

Do I have a Mk1 or a Mk2 engine now? Is it a factory replacement engine (cf. "ESS")?

Thank you in advance!

Kind regards, Dieter.

[AlanD]

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Hi Dieter,

if you log onto the Rimmer web site, they have details of engine no's etc with dates and an explaination of the engine codes,i'm sure others can enlighten you also



Alan

[Arbman Al]

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Hi Dieter,

Been mentioned before here:

http://stagownersclub.mywowbb.com/view_topic.php?id=4085&forum_id=1&highlight=V3293

Rgds....Al

[DJT]

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Dieter,

You have an early block, but the ESS suffix denotes a factory exchange item. Probably under warranty.

The heads are Mk2 denoted by the V3293 and V3294 numbers. Mk1 heads have V3142 and V3143.

The long part numbers beginning with 88 also denote later castings as the earlier ones did not have the 88 prefix. This was introduced as part of the BL rationalisation. There were some Mk1 castings produced with the 88 prefix as spare parts.

Dave

[Dieter H. Marschall]

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Hello again,

Sorry, there was a typo in my first mail: The chassis no. is LD 10250 BW (not LD 1025 BW).

So far my assumptions are:

- factory replacement engine, hence the "ESS"

- early Mk1 engine, hence the low no. (LF 804)

- late Mk2 heads, hence the "V3293/4" and "88313210/1" imprint

So I will have to find out with a stetoscope, whether the pistons are flat (Mk1) or domed (Mk2). Flat pistons would mean less compression and less power. But then I would not understand why the engine is "tinkling" when accelerating. Domed pistons would explain the "tinkling" after the heads were plained minimum once - although a thick Payen gasket was used.

Cananybody please confirm or correct my views?

Thank you in advance, Dieter.

[nib]

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Hi Dieter

I do believe domed pistons have been hard to get hold of for sometime so you may have flat top pistons if its needed them in the last few years,I dont think you would lose a lot of performance as originally a MK1 was quoted at 145bhp and MK2 at 146bhp.

When you say tinkling is this what we call pinking,a horrible tapping noise when accelarating.Have you checked your timing recently?

Mark

[Dieter H. Marschall]

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Hello Mark,

Thank you for your kind help.

I am afraid the combination of flat pistons and Mk2 head would mean considerably less power, as the combustion area in the Mk2 heads is bigger to compensate for the domed pistons. So with Mk1 pistons and Mk2 head this means less compression.

The timing is already set at 11°, but there is still a pinking when accelerating.

Best wishes, Dieter.

[nib]

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Hi Dieter

My car was recently running ok with a MK2 l/hand head,a MK1 r/hand head with flat top pistons,I never had it performence checked but general motoring was fine,I would have thought there was quite a few people running flat pistons and MK2 heads on here,they might be able to shed some light on the subject with more knowledge than myself.

Mark

[Dieter H. Marschall]

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nib wrote:

Hi Dieter

My car was recently running ok with a MK2 l/hand head,a MK1 r/hand head with flat top pistons,I never had it performence checked but general motoring was fine,I would have thought there was quite a few people running flat pistons and MK2 heads on here,they might be able to shed some light on the subject with more knowledge than myself.

Mark

Hello Mark,

You are right. As I -as an old man- hardly ever drive at high speed, I would never heve realized this loss of power. But other people pointed out to me that there might be an issue.

Kind regards, Dieter.

[flying farmer]

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The Stag engine fitted to my estate is a mark two with flat top pistons and I measured the combustion chamber volumes and found it gave a compression ratio of 8.5:1, with standard thickness gaskets.I think mark ones were 8.8:1 and mark twos were 9.2:1.

The engine currently in the stag has domed pistons and well skimmed heads with standard gaskets and has about 10:1 compression ratio

Oddly enough the higher compression engine runs 16 degrees static advance, and the lower compression engine 14 degrees, both pink occasionally if I pick up a tankful of crap fuel but are otherwise ok on standard unleaded

The Stag engine in the TR has 10.2:1 compression and runs best at 18 degrees of advance and also has extra weak advance springs to give a faster advance curve, but since this has different cams this is not particularly relavent

Back in the days I was running a PI saloon, Chris Witor did an article about the high performance 2 litre staight six in his mark one saloon. From what I remember he used early flat pistons and a skimmed block to raise the compression ratio rather than the later domed pistons, and IIRC this was because the dome on the piston slowed the flame front across the cylinder.

If this is the case, then it may be that the domed pistons need more advance anyway, so the extra compression does not actually cause a pinking problem f you have a mix of mark one and mark two heads:?

Neil

[Dieter H. Marschall]

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Hello,

I used an endoscope today and found out that the piston tops are flat. So I do have Mk2 heads, but Mk1 pistons.

We measured compression as well: 10.0 to 11.0 on all the eight cylinders.

Thus the good news is: That engine has less power, but hopefully a longer lifetime.

Best wishes, Dieter.

[Dieter H. Marschall]

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