M20b25 Scuffing on pistons and cylinder Wall HELP pls

[GarbageCanE30]

Just pulled out my pistons and noticed some scuffing on all 6 favored to one side throughout each cylinder. Do you think I need to rebore/get larger pistons and a different crank, or just a hone and new pistons? I know wear like this is pretty common but it's the vertical scuffs on the cylinder walls that concerns me a bit. Does anyone know what causes wear like this? Here are a few pics:

[McGyver]

The only way to know if those pistons are still good is to measure them, the Bentley manual should have the tolerances in it.

That being said, I would put money on it that those pistons are trashed. It's likely time to buy a set of overbore pistons and then bore your block to match. Here a set of the 2nd overbore for $550:
https://www.autohausaz.com/pn/108961...xoCOXEQAvD_BwE

Or, you could get custom higher compression pistons for like $850 and have a bump in power:
https://www.iemotorsport.com/product...ts/e30-engine/

[GarbageCanE30]

The only way to know if those pistons are still good is to measure them, the Bentley manual should have the tolerances in it.

That being said, I would put money on it that those pistons are trashed. It's likely time to buy a set of overbore pistons and then bore your block to match. Here a set of the 2nd overbore for $550:
https://www.autohausaz.com/pn/108961...xoCOXEQAvD_BwE

Or, you could get custom higher compression pistons for like $850 and have a bump in power:
https://www.iemotorsport.com/product...ts/e30-engine/

Got ya, thanks for the response. Seems like a lot of people have very similar wear on their pistons with m20s as all of the people I've found with even low mileage pistons for sale, have very similar scuffing. Mine do seem to be a bit deeper. As for the actual cylinder wall, did you think just a rehone could fix that? Unfortunately I'm not sure how much I trust the machine shops around me for most of this stuff after calling a few :/

I saw your comment on my other "should I swap" thread, and I appreciate that response a great deal as well. I weighed my options and decided to build my m20 which I'm very glad I opened up, as there was a lot of fairly serious stuff that could've led to some failure points. It also gave me info about this car I wouldn't have otherwise had.

With that being said, I ultimately decided to do a turbo build using the old dinan kit that's floating around right now with modern engine management, which brings me to my next question. In my other post you mentioned difficulties doing a megasquirt build, and I'm curious as to what you meant by that. Is it not as simple as installing it to your harness, and then getting a tune from a reputable tuner? I'm really excited about this build path as it keeps the engine bay looking fairly stock, is a cool period correct high end mod, and it gives my motor a healthy boost of power (about 300 hp on 10 psi) which is well within safe limits for the m20 to my understanding.

However, I am still new to this and probably very naive to the ins and outs of building and figuring out these older cars. I'm looking to do a full restoration of my IS, and I want it to be an exciting and unique end product. I don't mind taking the time to make it as close to perfect as I can, and I have the resources to do so, but hearing from people who have been through this and know what to expect is enormously useful for me, so thank you again for any information you have provided and can provide about this topic

[TobyB]

It's very hard to tell by looks-

do you know if this engine has been apart before?

If it's factory honing we're seeing in your pics,

AND

you're cleaning up an engine for a regular old street car,
then it's worth measuring the bores to see if they're 'close enough'
to try re- honing. A good flat hone (not a dingleball) will confirm that
IF you watch carefully as you start. The hone's really good at showing
relative wear, but it takes a pretty careful read as you start it.

Then, yeah, you'll get a 'newer' engine that performs well- maybe as well as stock.

But if you're a perfectionist, or want 'better than average' ring seal, time for the
whole meal deal.
Each course is reasonable, but the tab at the end of the night is usually pretty steep.

t

[McGyver]

Seems like a lot of people have very similar wear on their pistons with m20s as all of the people I've found with even low mileage pistons for sale, have very similar scuffing.

To be honest, those pistons would work just fine for some amount of time. I suggest replacement because its not that expensive, the parts are available, and it gets you back to factory specs. If you're going to build an engine, why reuse stuff to make a 50k mile engine when you and replace it for a 200k mile engine? That's what I meant by "it cost $$$ to build a reliable turn-key engine".

As for the actual cylinder wall, did you think just a rehone could fix that?

I don't have enough experience to answer that, its probably a question for Digger. I do remember seeing a thread lately where someone had some scuffs before honing that turned into grooves after honing once the glaze was removed. All that being said, you plane to build a boosted engine with higher cylinder pressure, shouldn't you go for the best possible seal? Would it work as-is? Probably. Do you want to risk needing another rebuild in the near future?

In my other post you mentioned difficulties doing a megasquirt build, and I'm curious as to what you meant by that. Is it not as simple as installing it to your harness, and then getting a tune from a reputable tuner?

Nothing about MegaSquirt is simple until you've done it several times. MegaSquirt can do anything, so there is no "correct" way to do it and the learning curve is dauntingly steep. You'll need to figure out your goals to figure out which version of MegaSquirt you'll need, and even then you may need to modify the circuit board. A lot of the info out there is either obsolete (~2007 on MS1 or MS2 while Extra was still in beta), or it's unreachable because the domain expired. Buying a Plug-and-Play box makes the install easier and you have someone who you've paid to help you, but you may be limited in your options (electronic boost control, launch control, running AC or an Aux fan, knock sensors, etc.).

Read through my thread on it. I've spent months (on and off) reading wiring diagrams for my car, for the e36 (for the TPS wiring), the MegaManuals, and I was still incorrect about several things. Once I re-solder some wires, I think I've finally figured out the wiring. This is probably over a hundred hours of research to become an expert on my specific install. I feel like I could figure out someone else's install, but that would be difficult and take forever.

Varg and Who-d-Who would be some of your best resources on MegaSquirt.

[GarbageCanE30]

HQUOTE=McGyver;n9920313]

To be honest, those pistons would work just fine for some amount of time. I suggest replacement because its not that expensive, the parts are available, and it gets you back to factory specs. If you're going to build an engine, why reuse stuff to make a 50k mile engine when you and replace it for a 200k mile engine? That's what I meant by "it cost $$$ to build a reliable turn-key engine".



I don't have enough experience to answer that, its probably a question for Digger. I do remember seeing a thread lately where someone had some scuffs before honing that turned into grooves after honing once the glaze was removed. All that being said, you plane to build a boosted engine with higher cylinder pressure, shouldn't you go for the best possible seal? Would it work as-is? Probably. Do you want to risk needing another rebuild in the near future?



Nothing about MegaSquirt is simple until you've done it several times. MegaSquirt can do anything, so there is no "correct" way to do it and the learning curve is dauntingly steep. You'll need to figure out your goals to figure out which version of MegaSquirt you'll need, and even then you may need to modify the circuit board. A lot of the info out there is either obsolete (~2007 on MS1 or MS2 while Extra was still in beta), or it's unreachable because the domain expired. Buying a Plug-and-Play box makes the install easier and you have someone who you've paid to help you, but you may be limited in your options (electronic boost control, launch control, running AC or an Aux fan, knock sensors, etc.).

Read through my thread on it. I've spent months (on and off) reading wiring diagrams for my car, for the e36 (for the TPS wiring), the MegaManuals, and I was still incorrect about several things. Once I re-solder some wires, I think I've finally figured out the wiring. This is probably over a hundred hours of research to become an expert on my specific install. I feel like I could figure out someone else's install, but that would be difficult and take forever.

Varg and Who-d-Who would be some of your best resources on MegaSquirt.


[/QUOTE]
So the dinan kit I'd be buying has a whodwho set up that comes along with it so I assumed itd be a bit more plug and play. Obviously I assume it still won't be easy or perfect, but it saves me from having to solder the thing in place and trial and error for the foreseeable future. As for the pistons, I'm definitely going to replace them if I can find a good set, however I don't think it makes sense until I figure out if I'm going to need a full on bore job, which honestly I don't know anyone who can take a look in person and tell me, and unfortunately, as tobyb suggested above, I don't really have the knowledge to look at it myself and understand the state of wear the cylinder walls are in. I've been doing as much reading as I can about this and unfortunately it's all very situational and speculative.

[GarbageCanE30]

It's very hard to tell by looks-

do you know if this engine has been apart before?

If it's factory honing we're seeing in your pics,

AND

you're cleaning up an engine for a regular old street car,
then it's worth measuring the bores to see if they're 'close enough'
to try re- honing. A good flat hone (not a dingleball) will confirm that
IF you watch carefully as you start. The hone's really good at showing
relative wear, but it takes a pretty careful read as you start it.

Then, yeah, you'll get a 'newer' engine that performs well- maybe as well as stock.

But if you're a perfectionist, or want 'better than average' ring seal, time for the
whole meal deal.
Each course is reasonable, but the tab at the end of the night is usually pretty steep.

t

I consider myself a perfectionist for better or usually, for worse... (For my wallet at least) I called several machine shops by me yesterday, one had no idea what I was talking about when asked if they could hone my cylinders, and the other guy, for some unknown reason, got kind of mad and snappy at me when I asked about that and a valve train clean up, and proceeded to quote me 475 just for the head refresh. (This seemed like a lot)

I'm fairly sure the motor was opened up though, but not sure to what extent. When I took off the valve cover I found 2 welded rocker journals and metric blue studs so there was definitely some abuse on this motor. Not sure if rings were ever replaced, and I'm not in good terms with the previous owner as I feel he was largely dishonest about the state of a car I am looking to basically frame off restore.

I don't mind spending the money as long as the end result leaves me with peace of mind and increased reliability/performance. I'll probably have to trek into jersey to find a competent machinist which isn't a problem for me, I just still have no idea what I'm doing...

[McGyver]

So the dinan kit I'd be buying has a whodwho set up that comes along with it so I assumed itd be a bit more plug and play. Obviously I assume it still won't be easy or perfect, but it saves me from having to solder the thing in place and trial and error for the foreseeable future. As for the pistons, I'm definitely going to replace them if I can find a good set, however I don't think it makes sense until I figure out if I'm going to need a full on bore job, which honestly I don't know anyone who can take a look in person and tell me, and unfortunately, as tobyb suggested above, I don't really have the knowledge to look at it myself and understand the state of wear the cylinder walls are in. I've been doing as much reading as I can about this and unfortunately it's all very situational and speculative.

I consider myself a perfectionist for better or usually, for worse... (For my wallet at least) I called several machine shops by me yesterday, one had no idea what I was talking about when asked if they could hone my cylinders, and the other guy, for some unknown reason, got kind of mad and snappy at me when I asked about that and a valve train clean up, and proceeded to quote me 475 just for the head refresh. (This seemed like a lot)

Having his PnP is a double edged sword: It may be easier to plug it in and you have a technical resource (if he doesn't mind helping the 2nd owner), but you'll need to figure out if the previous owner made any mods.

I just had an m30b30 head freshened up to essentially original condition (hot tank, skim the head, clean and inspect the cams, new valve seals, etc.) and it cost $620. By comparison $475 is cheap, but my guy has 30+ years of experience rebuilding $$$ German engines (1960's Mercedes aluminum blocks). I'm happy spending the extra cash to know it was done correctly the first time.

If you're going to replace the pistons, I would suggest at lease a 0.25mm overbore (1st O/B) to make sure the walls are round. Since you're going turbo, maybe think about custom forged pistons rather than stock (but I'm biased). For my build, my m20b25 crank is trashed, block needs a bore, so I bought a m20b27 seta hoping to use the seta rotating assembly and a 325i 885 head. (The seta 885 head has single valve springs, different cam, and needs oil passages drilled) I have some scoring in the seta block, which likely means an overbore and custom pistons.

[GarbageCanE30]

Having his PnP is a double edged sword: It may be easier to plug it in and you have a technical resource (if he doesn't mind helping the 2nd owner), but you'll need to figure out if the previous owner made any mods.

I just had an m30b30 head freshened up to essentially original condition (hot tank, skim the head, clean and inspect the cams, new valve seals, etc.) and it cost $620. By comparison $475 is cheap, but my guy has 30+ years of experience rebuilding $$$ German engines (1960's Mercedes aluminum blocks). I'm happy spending the extra cash to know it was done correctly the first time.

If you're going to replace the pistons, I would suggest at lease a 0.25mm overbore (1st O/B) to make sure the walls are round. Since you're going turbo, maybe think about custom forged pistons rather than stock (but I'm biased). For my build, my m20b25 crank is trashed, block needs a bore, so I bought a m20b27 seta hoping to use the seta rotating assembly and a 325i 885 head. (The seta 885 head has single valve springs, different cam, and needs oil passages drilled) I have some scoring in the seta block, which likely means an overbore and custom pistons.

So the original owner of the MS2 actually never installed it or messed with it and was still using the original dinan turbotronics engine management from the 90s, but it began to fail towards the end of its run.

Got ya tho, guess that price isn't too terrible but man when I call a business and greet the person who answers the phone, and get "yeah?" As a response, it doesn't give me great confidence in their customer service/the work they do. Out of the 4 shops I could find that actually do this kind of work, EVERY one of them has been terrible on the phone and isn't a place I'd trust with my money. I shouldn't have to ask you if I'm calling the right number for a business... What would a .25mm overbore bring the displacement to? Are there ots forged pistons that will fit a .25mm overbore? There's no real handbook for this stuff so I thank you for the help and knowledge.

With the condition of my head as seen here, I'm not sure how to proceed. I've been thinking about getting another 885 head that's already been cleaned up if someone has one. Overall it's pretty clean but I don't like the idea of these welded bits under my valve cover, even if it's functionally acceptable.

[Kershaw]

The welded bits are fine. What's crazy are your headbolts. I have never see them before. Marine grade coated bolts? They certainly aren't any "m20" head bolts I'm familiar with.

[GarbageCanE30]

[QUOTE=Kershaw;n9920354]The welded bits are fine. What's crazy are your headbolts. I have never see them before. Marine grade coated bolts? They certainly aren't any "m20" head bolts I'm familiar with.[/QUOTE

Yeah theyre apparently known as metric blues and we're a popular "upgrade" option back in the day among tuners. The improvement of them over the stock head bolts seem to be widely debated. I'm not a fan.

[lukeADE335i]

They were definitely an upgrade over the hexagonal M20 head bolts, that liked to shear the heads off and lunch your engine. As they're stretch bolts, they should be replaced for the updated M20 torx head bolts anyway in any rebuild.

I presume if you're going to turbo your engine you'll go for ARP head studs?

[GarbageCanE30]

They were definitely an upgrade over the hexagonal M20 head bolts, that liked to shear the heads off and lunch your engine. As they're stretch bolts, they should be replaced for the updated M20 torx head bolts anyway in any rebuild.

I presume if you're going to turbo your engine you'll go for ARP head studs?

Yes sir, not rushing grabbing them hoping to find a set of arps for sale. Not looking so good for that so I'll probably end up scooping them from ECS/FCP after I get my head and block back.

[BUDNUNTA]

i think the old school method to repair that is to knurl the pistons, it will swell them out some and hold a bit extra oil

[ForcedFirebird]

Those broken rocker shaft bosses is surely from a broken timing belt. If you are having the head machined, have them check the valve guides and seat run-out. Often times when a belt fails the valves stems will get bent and ream the inside of the guides. Many machine shops don't replace, or even line them. Also let them know the guides are 6.98mm, not 7mm. I've had heads come in the shop that were "rebuilt" and the guides were just reamed/lined and opened back up to 7mm - which is WORSE than a worn guide. If the guides are ruined, best to replace them, just be cautious as there are 3 sizes of guides and you won't know which ones are in your head until one is pulled and mic'd.