M20 cylinder walls - need hone and re-ring or no?

[the_eskimo_wonder]

I picked up a running-when-pulled M20B27 from a friend's trusted shop for $100 to begin my 2.7i engine build. Engine was complete but had been sitting in the corner of the shop for a while. I stripped it down to the short block yesterday and was a little surprised to see the cylinder walls with quite a bit of visible cross-hatching. I don't know how many miles are on this engine or if it's been rebuilt in the past. From everything I saw it looks very clean on the inside (I pulled the oil pan and looked great under there. Head is also in good shape aside from some carbon buildup to match the pistons).

So here's my question... Does this seem normal or am I looking at a problem? Did the rings never fully seat? Cylinder walls have a perfectly smooth feel with fingertips but a nail can feel the hatching still. Can I clean the pistons, clean and wipe everything down with oil and button it back up?

[zaq123]

I picked up a running-when-pulled M20B27 from a friend's trusted shop for $100 to begin my 2.7i engine build. Engine was complete but had been sitting in the corner of the shop for a while. I stripped it down to the short block yesterday and was a little surprised to see the cylinder walls with quite a bit of visible cross-hatching. I don't know how many miles are on this engine or if it's been rebuilt in the past. From everything I saw it looks very clean on the inside (I pulled the oil pan and looked great under there. Head is also in good shape aside from some carbon buildup to match the pistons).

So here's my question... Does this seem normal or am I looking at a problem? Did the rings never fully seat? Cylinder walls have a perfectly smooth feel with fingertips but a nail can feel the hatching still. Can I clean the pistons, clean and wipe everything down with oil and button it back up?

looks like typical M20 block. Mine looked like that with 160k miles on the clock. It all depends how much of a build you are doing. Are you pulling the crank out and replacing bearings? New rings etc?

If yes to the above, I would at least make sure that bores are still round and not damaged all the way through, slightly re-hone it for new rings, pull oil gallery plugs on each side and clean the block very well inside and out. Check the deck to make sure it is still true and you should be good.

[the_eskimo_wonder]

Wasn't planning on it. Was hoping to just toss a rebuilt, cammed 885 on top with injectors, headers, and tune and call it a day

[zaq123]

Wasn't planning on it. Was hoping to just toss a rebuilt, cammed 885 on top with injectors, headers, and tune and call it a day

you said engine build

anyway, if that is your plan, just wipe/vacuum everything clean, including the deck so your HG seals well. Don't scrub carbon from pistons, no need for that. Just wipe them with a rag and some kerosene. DO Not use abresive paper or Scotchbrite pads anywhere near that block, unless you plan to disassemble and wash the whole thing clean.

Have fun

[e30davie]

Did you compression test it before pulling it appart?

Based on your description and those photos its a good sign. But Always a risk i suppose.

Pending how dodgy you want to be you could put the head back on with teh old head gasket and timing belt and give it a compression test. But might be alot of effort for not much gain.

If it were me and I opened an engine and it looked like that, I would probably take the risk and run it.

[95BMWIC]

Wasn't planning on it. Was hoping to just toss a rebuilt, cammed 885 on top with injectors, headers, and tune and call it a day

If you are putting that much effort into it - (and since it is already disassembled) pull the pistons, measure, install new rings and check main / crank bearings to ensure bottom end is perfect..

You could also buy an "e" crank and with a little planing of the deck, build yourself a sweet little stroker motor..

[SkiFree]

If you are putting that much effort into it - (and since it is already disassembled) pull the pistons, measure, install new rings and check main / crank bearings to ensure bottom end is perfect..

This. At a minimum I would disassemble and take to a machinist to measure/hone.

Plan for the worst, hope for the best. Are you going to do this right, or go with hoping it works? If you decide to put it back together and run it as is, I certainly hope you aren't going to blame anyone but yourself if something goes sideways.

[the_eskimo_wonder]

Well the more I dive in, the more I realize if I'm going to be into it a grand, I might as well be in for $1200-1400. Going to pull the crank and check all the bearing tolerances, as well as hone and re-ring. Can I check the connecting rod bearing tolerances without disassembling them? All these non-reusable TTY bolt sets really start to add up.

Really wish I had cranked it and gotten compression numbers before I pulled it apart

[e30sh]

You can use the old head gasket, old head bolts and even your new head if it's ready and do a leak down test. It's a great tool for finding where your compression leaks are coming from.

[Andre3127]

If you are putting that much effort into it - (and since it is already disassembled) pull the pistons, measure, install new rings and check main / crank bearings to ensure bottom end is perfect..

You could also buy an "e" crank and with a little planing of the deck, build yourself a sweet little stroker motor..

OP says that engine is a b27 which already has the eta crank, because it's an eta engine.

[95BMWIC]

OP says that engine is a b27 which already has the eta crank, because it's an eta engine.

Nice catch Andre ..

Advice stays the same -

but if the stroker is something you are after - keep the crank - just switch out to "i" domed pistons with the "i" head. Im assuming thats what you are doing from your first post.."2.7i engine build.

[SkiFree]

Well the more I dive in, the more I realize if I'm going to be into it a grand, I might as well be in for $1200-1400. Going to pull the crank and check all the bearing tolerances, as well as hone and re-ring. Can I check the connecting rod bearing tolerances without disassembling them? All these non-reusable TTY bolt sets really start to add up.

Really wish I had cranked it and gotten compression numbers before I pulled it apart

Hey, that's great news.

I don't normally do this, but given you seem to be on the right path... if you are in the LA/Pasadena area, I can give you the name of an extremely good (and fairly priced) machinist.

[zaq123]

Well the more I dive in, the more I realize if I'm going to be into it a grand, I might as well be in for $1200-1400.

welcome to the madness.

[the_eskimo_wonder]

I tossed the original head gasket during tear down so that option is out. I'm going to go ahead and do it right. Going to strip everything out, go through the bottom end completely and make sure it's perfect before slapping the head on. Going to use the eta pistons as there's a strong chance this engine will see a turbo in the next few years (even more reason to do the bottom end).

SkiFree, I appreciate the offer but I'm up in the SF Bay area. I've found some good recommendations in the area though.

And to think, this started as a free car. On the upside I've definitely earned the respect of my neighbor who's been restoring a factory Alpina 2002 racecar for the last 15 years

[SkiFree]

And to think, this started as a free car. On the upside I've definitely earned the respect of my neighbor who's been restoring a factory Alpina 2002 racecar for the last 15 years

Mark is your neighbor?

Good luck on the project!