Headgasket issues?

[alpinaseeone]

Hi all,

Seeking some help of the M20 Gods on here. Very new to forced induction so excuse my stupidity in advance.

Some background info: Recently blew my M20B25 (bought used from someone) which was stock except ARP studs and an MLS HG. Ended up melting a piston in Cyl 5 and blowing the rings / ring lands in 1 & 6. I think either the timing was too aggressive but not sure exactly how it happened. Instead of rebuilding bottom end, I found a stock ETA bottom end and wanting to try the 'budget stroker' out, I re-used the 885 Head from the 2.5 on this with the ARP studs and ran it with an Elring HG.

With the help of Panici in the passenger seat tuning the MS2PNP, the car seemed to be handling okay. No real problems except some blow-by. Hoping to solve at least some of this with a catch can set up soon.

The real problem came when we were doing a 5th gear pull. Started at around 90km/h and pulled to ~ 200. Got to around 6k rpm and a huge cloud of smoke let out the back and the temp gauge shot right up. Pulled over on the side of the highway and popped the hood to find coolant all over the drivers side of the bay except in the expansion tank. Unfortunately we had no coolant with us but shut everything off and let it cool down for a while. Tried again to start and had no luck whatsoever. It sounded like there was some compression still but for sure a couple of cylinders were missing so didn't try any more. The car didn't see any more than 8.7psi in this run and the timing map showed it at 13deg. I'll throw up some screenshots of the timing, fuel and AFR target maps tonight.

SO,

In my limited knowledge I'm thinking it could be one of three things:

1. Cylinder head wasn't flat enough or is cracked without me knowing - When I pulled the head from the 2.5 block it had very recently been machined and I couldn't see any visual signs of cracks. Checked with a straight edge but no feeler gauges and *looked* ok. (stupid mistake I know)
2. Head gasket wasn't seated properly or incorrectly installed (I prepped both surfaces using a 3M Roloc Bristle disc (Yellow 80 Grit) and made sure both were clean of gasket material before install)
3. The studs weren't torqued enough - I did 3 equal steps to 70 ft/lbs but DIDN'T retorque as I'm learning some people demand doing after a heat cycle.


If anyone can help I'd really appreciate it. Current plan is to pull the head, already ordered an OEM BMW Headgasket, I'll get the head pressure tested and resurfaced to ensure flat and then try again with lower boost?

[Panici]

Just to add an additional datapoint, I was watching AFRs during the pull and we were in the high 10s low 11s.
So it didn't lean out (unless one injector is flowing drastically differently then the other 5?)


I don't suspect timing, although we should do a fixed timing test to see if we are getting any drift with RPM increase.

[MrBurgundy]

You have to start with a leakdown test and see where the compression is going. Obviously this is some internal failure and when you see low compression across multiple cylinders, its most likely a HG failure. Since the coolant system blew, it's most likely a compression leak to the cooling system. If you're lucky, its because of an HG failure.

Post your AFR/Ignition map. 13* is extremely conservative at 9psi

It's probably having a hard time burning the fuel at higher RPMs if the ignition timing around 13* if anything

[Panici]

Post your AFR/Ignition map. 13* is extremely conservative at 9psi
It's probably having a hard time burning the fuel at higher RPMs if the ignition timing around 13* if anything

Maps attached.
We were still roughing in the VE table, think this was one of the first WOT pulls.

I didn't realize we pulled all the way to 6000rpm, I thought we got to 4000-ish.
This would actually put us at 14-15* @ 160kpa.

Wish I had logging enabled for exact data.
We were having laptop issues and had to dump the project to my computer, and I didn't start a new log after that.

[MrBurgundy]

Yeah, not having the exact data is kinda a killer here..

Like, those numbers are fine... If that's actually where it was at.

Without the exact data, next best thing to diagnose the issue is tear the motor down and see what happened.

[alpinaseeone]

Okay small update - Had some time yesterday night to tear everything apart and thankfully looks as though it was HG failure.

Tested compression and had ~160psi in first 5 cylinders except 10psi in #6. Pulled the head to inspect:



Now, if this was caused by a warped head or incorrect torque I don't know. Current plan is to get it off to a machine shop for pressure testing and resurfacing and then try again being a little more conservative with the boost until I know it's safe.

Anyone on here have recommendations for using ARP studs?
Wondering if I installed wrong - Process was to clean all threads with ARP chase tool, remove gunk from holes then hand-thread each stud into the block. For the head, I used ARP assembly lube on both sides of the washer and underside of the nut and torqued 3 equal steps to 70ft/lbs.

Thinking that this time I'm going to reinstall studs and make absolutely sure nothing in the holes and additionally re-torque studs again after a heat cycle.

[MrBurgundy]

Looks like it either wasn't torqued enough, or uneven sealing surface..

Make sure when you lube the hole for the stud to use minimal lubrication... I personally do not lube anything except the washer under the nut.

If you use too much, it can prevent the stud from going down into the block far enough.

How did the nuts feel coming off around cylinder 6?

My money is on something is warped. That compression ring is way out there.

[alpinaseeone]

Looks like it either wasn't torqued enough, or uneven sealing surface..

Make sure when you lube the hole for the stud to use minimal lubrication... I personally do not lube anything except the washer under the nut.

If you use too much, it can prevent the stud from going down into the block far enough.

How did the nuts feel coming off around cylinder 6?

My money is on something is warped. That compression ring is way out there.

Any tips as to how much lube to use? Seriously though - maybe I used too much and the studs didn't hold properly. It was my first time using these.

Cylinder 6 studs felt pretty solid tbh, not like they were any more loose than the others

[MrBurgundy]

Any tips as to how much lube to use? Seriously though - maybe I used too much and the studs didn't hold properly. It was my first time using these.

Cylinder 6 studs felt pretty solid tbh, not like they were any more loose than the others

If you lost a hold on the gasket because of the nuts being under torqued, you should feel that when loosening them up.

I'm reading back on the original post and remembered you melted a piston, which is why you're on the 2.7 block now.

885 heads do not like heat at all. I would not be surprised if that thing got damaged when it first went kaboom. At this point you need to send the block and head to a machine shop to guarantee that everything is flat and straight.

Ideally they're going to tell you the block or head was warped. Then you can rebuild with confidence because you'll have your answer to why the HG failed. When the resurface the head/block ask them to take a pic after the first pass so we can all see what it looks like, assuming its warped. Obviously, looking for paint to be left around cylinder 6 on either surface

How did the HG look when the engine failed on the 2.5 block?

[alpinaseeone]

I'm reading back on the original post and remembered you melted a piston, which is why you're on the 2.7 block now.

885 heads do not like heat at all. I would not be surprised if that thing got damaged when it first went kaboom. At this point you need to send the block and head to a machine shop to guarantee that everything is flat and straight.

Ideally they're going to tell you the block or head was warped. Then you can rebuild with confidence because you'll have your answer to why the HG failed. When the resurface the head/block ask them to take a pic after the first pass so we can all see what it looks like, assuming its warped. Obviously, looking for paint to be left around cylinder 6 on either surface

How did the HG look when the engine failed on the 2.5 block?

Yup that's the plan! I've pulled it from the car and hopefully leaving it with a local shop tomorrow.

2.5 HG was an MLS gasket so only pistons and rings saw the brunt of the damage in that episode. I'm assuming that's why some people don't like the MLS as much as it's more likely to damage other internals, hence the fitting nickname 'boost fuse' for a composite HG.

[Northern]

+1 to the machine shop pressure test/resurface. I hope it finds something.

If they say it's fine:
Any thoughts on your injectors? You see AFR is fine, so pump probably works but melting pistons/cracked ringlands/popped gasket sounds like detonation.
Unless your trigger offset is borked or you have some hidden modifier table doing something weird, I don't see how you'd do this from timing, so IMO that leaves fuel.

[alpinaseeone]

+1 to the machine shop pressure test/resurface. I hope it finds something.

If they say it's fine:
Any thoughts on your injectors? You see AFR is fine, so pump probably works but melting pistons/cracked ringlands/popped gasket sounds like detonation.
Unless your trigger offset is borked or you have some hidden modifier table doing something weird, I don't see how you'd do this from timing, so IMO that leaves fuel.

Thanks! Spoke to the machinist today (very reputable guy in Ontario) who took a quick visual at it and said it looked warped from what I'd described and the marks left behind on the head. Said he'd make a note to tell me how far out of spec it is when getting resurfaced. Managed to sneak me into his 3-month backlog and said it'll be ready in the next few days!!

The injectors were upgraded with the change to the 2.7 block so I'd hope that any detonation that I was experiencing when I melted a piston was resolved with the upgrade to bigger injectors. I remember with the older setup the injector duty cycle was above what was considered 'healthy' but I didn't manage to find new injectors before it went boom...

I guess we'll find out when everything's thrown back together how it holds up. Opting for an OE BMW Headgasket this time which feels more robust in hand compared to the Elring counterpart.

[MrBurgundy]

My 2 cents is go with an MLSHG again if the machinist is saying it was really warped, causing a compression leak. IDK how much boost you're trying to run, but even BMW nowadays is using MLS on all their forced induction applications.

Elring gaskets are great, so going OE bmw is not going to yield a more reliable setup. I'm pretty sure BMW is using Elring anyways.

[varg]

1. MLS is likely not necessary. I've run 20psi of boost (T3/T04E turbo) on a daily driven E30 with a stock head gasket and had no issues. Block prep is just as critical as head prep with ARP and these days I'd rather o-ring the block than risk leaks with an ARP gasket.
2. Timing advance numbers are always suspect because they're based on the tooth #1 angle. If the tooth #1 angle is wrong, your 13° could actually be 23°, or 3°, or anything. What is your trigger angle?
I have seen people use all sorts of wacky numbers, my verified with a timing light tooth #1 angle is 84°. Verify yours with a timing light in case something is different in your setup than mine.
3. You say you melted a piston, that's most strongly suggestive of a fueling issue, detonation will break of ring lands, crack pistons, put holes in them, but usually the melt is minimal. What kind of injectors were they? Are they flow matched? Had they been tested?
I have seen people melt down built engines because they cheaped out on injectors, never use anything old and used without flow testing and cleaning. Never use anything cheap (not a reputable brand) or off of ebay and untested. By the end of my time tuning other people's cars I'd tell them no if they had generic ebay injectors or something like that because I didn't want to be the guy with the laptop when a piston got turned into a piece of modern art.

Also, an ARP stud tip: if the washers aren't the type which are textured on the bottom in some way, sand the bottoms of the washers a bit on some coarse sandpaper, I think I used 100grit. It textures the bottom of the washer and keeps it from spinning on the head mating surface, which will alter your torque values. Clean the mating surfaces before dropping the washers in sanded side down and do not lubricate both sides. I've yielded and stretched an ARP stud mistakenly because when the washer slips, the torque drops, and I was in a hurry and kept pulling on the torque wrench even though I should have known better when the torque plateaued. Luckily I had the presence of mind to realize what I had done right after.

[Panici]

2. Timing advance numbers are always suspect because they're based on the tooth #1 angle. If the tooth #1 angle is wrong, your 13° could actually be 23°, or 3°, or anything. What is your trigger angle?

3. You say you melted a piston, that's most strongly suggestive of a fueling issue, detonation will break of ring lands, crack pistons, put holes in them, but usually the melt is minimal. What kind of injectors were they? Are they flow matched? Had they been tested?

I can speak to these.

2. Before we started with this engine, I asked and
alpinaseeone said that he tested a fixed timing angle with a timing light at idle and had to adjust the trigger angle by two degrees to get a match. Tooth #1 Angle is currently set to 84deg.
Plan is to check again when it goes back together, and also vary RPMs to see if there is any timing drift.

3. Piston melt was on his previous engine failure. After I heard what happened I offered to help with the tuning. The most recent failure in this thread appears to be headgasket only.
Injectors are a used set of Siemens Deka 60#. I suggested to get them cleaned and tested to verify flow before the engine goes back together.