First M20 Rebuild/Stroker Questions

[cj197574]

I'm new to this forum and the BMW scene as I just purchased my friend's 325iX and it is in need of a fresh engine. I have some experience in engine building as I've helped put together two caterpiller diesel engines but this is my first go at the M20. As always, disassembly went quickly and I have two M20 engines that are completely taken apart. After finishing up the second one I realized that the gear drive for the oil sump is not very easily removable or at least I can't figure out a simple way to remove it and after doing some research it seems to be difficult to install correctly. Is it ok to leave these oil sump drive gears in the engine as it goes to the machine shop and gets cleaned, bored, honed, etc.?

Secondly, I'm building a mild stroker with a m20b27 crankshaft, 325i connecting rods, and custom ross pistons from Ireland Engineering. I have been able to find most everything that I need for this setup but I'm having a hard time finding a good set of injectors. I've read that about 19lb/hr is the sweet spot for a 2.7/2.8L stroker. Do you all have any recommendations for what I should be looking for?

[digger]

i would think the gear removal would be somewhat like on a regular 325i block. Remove the cap on the intake side of the block which is held on by a single bolt and pry cap off, the gear can be pulled out (atleast on 325i block). post up some photos of what your looking at. The issue is usually with intermediate shaft bearings.

have you ordered parts?
19lb from an M30 or any 2V/cyl engine should be fine for a mild engine, be aware that original units are getting old now and simply cleaning them is not as reliable as it was 10 to 15 years ago.

[cj197574]

Ok, I'll post some pictures tomorrow when I'm at the garage.

I've only ordered the crankshaft and a MegaSquirt so far. As for the injectors I work for a smaller performance fuel system company and I should be able to clean and flow test the injectors on a weekend to make sure they're still batched well. Are there any good options for buying new injectors or is buying used the way to go?

[digger]

i favour new injectors if you have the $$$ but haven't looked for good deals for legit injectors, a used set from somewhere reputable will most likely be ok at save some coin.

what piston specs are you going to order?

[cj197574]

Ok, I'll price out some new injector options first and then check the used market if its outside of my budget.

Quite honestly I'm up in the air about the bore for the pistons. I was originally thinking of trying to just get the cylinders honed/re-crosshatched if they're in spec and order 84mm pistons with 10:1 compression. However, I know that cylinders are usually machined after the pistons are measured to make sure everything fits together well and if I'm paying to get the cylinders bored I may as well go to 85 or 86mm. I'm not trying to go crazy money wise on this build but I do realize that messing with engines takes some $. Do you have any thoughts on the matter?

[digger]

For a 2.7L street engine i would get a forged set as follows:
- 85mm bore
- OE 9.7:1 style dish-dome ( will end up approx~10-->10.5:1 CR),
- 4032 alloy.
- valve reliefs cut for something like a 288 or 304 cam depending how likely you want to go wild down the track
- compression height to suit 135mm rod/81mm stroke and stock 1.75 gasket
- Ask how much extra a set of conventional set of total seal rings with Napier style second ring (do not ask for gapless too much $$$ and no real benefit)

Steve from Top End can do these as he has the scans for from the OEM pistons, other places will give you a more or less random shape piston dome which while they still function they have no development behind them.

These pistons will result in a decent bump in CR but still ok for 93 octane with proper tuning, it will use the OE style piston dome to retain the same combustion characteristics and use the more durable high silicon alloy. It will still use the EO head gasket and have plenty of piston to valve clearance.

[cj197574]

Fantastic, thank you. These suggestions are really helpful. Can you break down what you mean when you mention total seal versus Napier style versus gapless piston rings? Are these just manufacturers or are there significant design differences?

[digger]

normally top end (dealer/ distributor for JE) will sell JE brand pistons which come with JE affiliated rings. The pistons can be designed for any rings though

Total seal is a specific brand of rings

total seal brand are best known for gapless rings (two piece ring) for either the top or 2nd ring. but their conventional rings (single piece rings) are really good.

the Napier ring is a type of 2nd ring that provides the best oil scraping so less likely to have oil consumption issues

so top end can spec the pistons (I.e. tell the manufacturer JE) for the total seal brand conventional rings.

[cj197574]

Oh ok I see. Thanks for clearing that up for me. As for the oil sump drive gears this is what I’m looking at:

[digger]

Remove the intermediate shaft from the front. Two flat head screws that secure the locking and thrust plate

remove the cup on the intake side. Carefully pry it up with flat head screw driver

the small gear will come out through the hole

[cj197574]

Ok, thank you. Should I remove the bearings that are in the block for the intermediate shaft as well?

[digger]

Ok, thank you. Should I remove the bearings that are in the block for the intermediate shaft as well?

no, replacing those seems to be a problem for many shops. some will reinstall the shaft when cleaning to avoid chemically damagaing the bearings if they are not replacing them.
if the bearings are bad you will need to replace them though, so speak to the shop

[cj197574]

Fantastic, thanks for the help.

[McGyver]

the small gear will come out through the hole

Be super careful when removing the shaft to avoid scoring up the bearing surface!