M20 conversion how to tell if 2.7

[E30_Jatt]

Hi guys,

I’m looking to do a M20 conversion and I am currently looking for a suitable M20 engine.

I have come across a supposed 2.7 for a good price, and was wondering if any of you guys on here could give me some guidance so I don’t get duped.

How do I tell if it is actually a 2.7 or just another 2.5?

What clues do I need to look for in determining if it is what he says it is.

Thanks

[sweep]

What is it a 525e bottom end?

[mark_i]

Look for the head ID stamp. 325i are 885.
Or remove rocker cover . 325e only have 5 cam journals

[Brianmoooore]

If it was born a 2.7, then the engine type number will start with 27. If it's a built up engine, then the only sure way is to measure the crankshaft stroke, which is easiest done by removing the sump.
You might be able to check with a slightly flexible rod though a spark plug hole with the piston at BDC, especially if you have a 2.5 engine to compare measurements with.
885 heads were used on some 2.7s as well as 2.5s. Most are marked 2.5 and 2.7 embossed into the casting.

[E30_Jatt]

Hi guys, thanks for all the info on what to look out for. The engine is definitely not a factory 2.7 it has been built afterwards. The seller has told me that the conrods were changed to shorter ones giving a longer stroke. Pistons were also changed and it has a super eta head. Does all of that sound about right?

[Speedtouch]

Shorter con-rods would give a shorter stroke!

[E30_Jatt]

Shorter con-rods would give a shorter stroke!

I did think exactly that when he told me, I’ll have to clarify that with him. He said it has been out of the car for 18-24 months.

With it having been out of the car for so long and not been run, is there anything that I would need to look at in particular?

Also I was reading on the wiki about the stamping on the head, which side of the block would I find the ID.

[steve_k]

if the engine is out the car then see if you can get the sump off,

once thats off have a look on the crank counter weights for either H/M75 for a b25 crank or H/M81 for a b27 crank,

[flybynite]

Shorter con-rods would give a shorter stroke!

Nah shorter rods give the same stroke it’s the crank that affects the stroke.

If he put a longer stroke crank in he would need shorter rods which is what he may have meant.

[Brianmoooore]

Shorter con-rods would give a shorter stroke!

Nah shorter rods give the same stroke it’s the crank that affects the stroke.

If he put a longer stroke crank in he would need shorter rods which is what he may have meant.

Exactly what I was just about to post.
Shorter rods with no other changes would just give an extremely low compression ratio and a good chance of the piston skirts hitting the crank weights at BDC.
Shorter rods used with pistons with a greater pin to crown distance and shorn skirts would restore the compression ratio and allow the crank to turn, but would still give the same cubic capacity.
Shorter rods used with a longer throw crank would work with the standard pistons if the extra throw of the crank is equal to the reduction in length of the rods, if due consideration is given to clearances of the skirts at BDC.
If the two aren't equal, then machining of the block deck, machining of the piston crowns, or the use of thicker head gaskets, as appropriate may be sufficient to compensate.

[E30_Jatt]

I have checked with the seller about the stamping on the head, he said it has 1705 885 stamped on it on the inlet side. Is that the correct head number for a super eta head?

[steve_k]

if the engine is out the car then see if you can get the sump off,

once thats off have a look on the crank counter weights for either H/M75 for a b25 crank or H/M81 for a b27 crank,

i'll say it again.

[Brianmoooore]

Super ETA head is 885 is standard 2.5 litre head.

[E30_Jatt]

if the engine is out the car then see if you can get the sump off,

once thats off have a look on the crank counter weights for either H/M75 for a b25 crank or H/M81 for a b27 crank,

i'll say it again.

Sorry bud not ignoring what you have said, I will only have a chance to look under the sump once I have bought the engine as the seller is not local and he is hesitant to do so himself. But he assures me it has the correct bits for a 2.7

[E30_Jatt]

Thanks for all the info guys really is helpful. So from what I have learnt on here, I think I’m gonna buy it.

The engine has been stored with the engine oil left in it, will this have caused any issues?

[Speedtouch]

Less chance of issues than storing it with no oil in it!

[steve_k]

if the engine is out the car then see if you can get the sump off,

once thats off have a look on the crank counter weights for either H/M75 for a b25 crank or H/M81 for a b27 crank,

i'll say it again.

Sorry bud not ignoring what you have said, I will only have a chance to look under the sump once I have bought the engine as the seller is not local and he is hesitant to do so himself. But he assures me it has the correct bits for a 2.7

not having a go bud,

it was just the fact that more "experienced" members seemed to be blind to the fact you said it was out of the car,

as for the seller being hesitant to check for you?? makes me wonder..........