Thoughts on cylinder condition m70

[ctuls]

Hi - I purchased an 1991 850 with ~80,000 miles a couple of months ago. I showed it to a E31 specialist in the bay area who felt that it drove well. However, I pulled spark plug from cylinder 1 on the M70 last week and wanted to get the thoughts and recommendations of the experts here as there is a lot of what seems soft carbon or oil deposits in the cylinder when borescoped.

This has definitely stressed me out so appreciate the help!

Cylinder 1 pic 3.jpgCylinder 1 pic 1.jpgCylinder 1 pic 2.JPG

[rjjablo]

What do all the rest of the plugs look like?

Might be a lot of short trips, 2,600 miles a year because its 30 years old

Oil comes from one of two places, Oil control Ring or Valve stem seals

Compression test and leakdown test if you are worried about the rings

New plugs, oil change and a couple long drives and pull and reinspect is what I would do

[TexaZ3]

Lots of carbon is sort of normal in these engines, all 80-s engines to be honest. Like suggested, swap new correct plugs, do an oil change and drive it at highway speeds for couple of hours - then see what the plugs/cylinders look like after. Compression tester is like $40 at most parts stores, takes couple of hours to measure for the piece of mind.

[ctuls]

Thank you both ! I have the brake booster out for a rebuild with Jay so should have much better access to all cylinders. Couple of questions:

1. Do I need to do both compression and leakdown, or can do just the leakdown ? I have an aircompressor at home and after doing some reading some places say leakdown is more comprehensive. But I am also new to both so might have misinterpreted the readings

2. The spark plugs in the car are BKR6EK, which I believe the PO replaced in the past 5K miles. Is a replacement still recommended? or can I attempt to clean them as they are newish

I am also going to work towards borescoping all other 11 cylinders this weekend @rjjablo

[dragon850]

Carbon build up is normal, quite a bit of short trips. If it's not smoking you're likely fine.
Change the PCV valves to be on the safe side and give it a good Italian tune up!
Who is this mystery E31 Expert in bay area out of curiosity)) I thought I was the only game in town LOL

[TexaZ3]

BKR6EK are correct plugs and likely are fine if new-ish.
Leakdown is more comprehensive, but also more complex. If you have never done it, it could be a learning curve to do it properly. Compression test is quicker and a good indicator of motor health overall, but does have some limitations. Generally, of your compression is good (I believe manual says anywhere from 146-174 is good for M70) then your engine is likely fine. Some initial exhaust smoke after sitting could be condensation, but check if still smoking at idle after long drive. When borescoping, take look at your valves, see if there any oil on the open ones.

[ctuls]

Hi All - I appreciate the replies, I had some family visit for the week and got side tracked. Also some how got frustrated and distracted, and ended up doing the transmission shifter seal and have the upper oil pan out for reseal. Ya know how it goes - one moment I am pulling out spark plug 7 next moment the subframe is dropped

@dragon850 and @TexaZ3: I don't believe it was smoking if I remember correctly. I hoping to scope all cylinders and do a leak down test over the next week or so. Sharing the pics of the spark plugs

@dragon850: I heard you are the best in the area. The shop, whose name I cant remember, is located in Berkley and the owner also has a E31. The people there were really nice. Ill look into the PCV replacement.

@TexaZ3: I have ordered a new set of spark plugs (BKR6EK), as it would have taken too long to clean, and got the OTC leak down tester.


Couple of notes on the plugs:

1. The numbering in the images is 1-6 = passenger side front to back, 7-12 drivers front to back
2. Almost all seemed to have some carbon and oil on them. I don't believe this is what good sparks should look like
3. Spark plug #3 had a little bit of unknown yellow deposit on them. Not sure if I should be concerned right now.
4. Most smelled like gas. That is likely due to me having to quickly shut off the car within seconds due to some noise. I got it towed after and havent started it

More pics in the next post. I have added a pic of the bottom end. In my opinion it looks fairly clean


IMG_7494 Large.jpegIMG_7501 Large.jpegIMG_7502 Large.jpegIMG_7503 Large.jpegIMG_7504 Large.jpeg

[ctuls]

IMG_7505 Large.jpegIMG_7506 Large.jpegIMG_7507 Large.jpeg

Let me know what you all think!

[TexaZ3]

Honestly, they look ok-ish, probably have leaking valve seals, so some oil gets on the plugs.

[chicosito]

Welcome to the e31 madness! I’m approaching 2 decades of ownership and it will be an amazing journey as you become familiar with your e31. If you’re local in the Bay Area and need anything, @dragon850 is the e31 guru for all your needs.

Hi All - I appreciate the replies, I had some family visit for the week and got side tracked. Also some how got frustrated and distracted, and ended up doing the transmission shifter seal and have the upper oil pan out for reseal. Ya know how it goes - one moment I am pulling out spark plug 7 next moment the subframe is dropped

@dragon850 and @TexaZ3: I don't believe it was smoking if I remember correctly. I hoping to scope all cylinders and do a leak down test over the next week or so. Sharing the pics of the spark plugs

@dragon850: I heard you are the best in the area. The shop, whose name I cant remember, is located in Berkley and the owner also has a E31. The people there were really nice. Ill look into the PCV replacement.

@TexaZ3: I have ordered a new set of spark plugs (BKR6EK), as it would have taken too long to clean, and got the OTC leak down tester.


Couple of notes on the plugs:

1. The numbering in the images is 1-6 = passenger side front to back, 7-12 drivers front to back
2. Almost all seemed to have some carbon and oil on them. I don't believe this is what good sparks should look like
3. Spark plug #3 had a little bit of unknown yellow deposit on them. Not sure if I should be concerned right now.
4. Most smelled like gas. That is likely due to me having to quickly shut off the car within seconds due to some noise. I got it towed after and havent started it

More pics in the next post. I have added a pic of the bottom end. In my opinion it looks fairly clean


IMG_7494 Large.jpegIMG_7501 Large.jpegIMG_7502 Large.jpegIMG_7503 Large.jpegIMG_7504 Large.jpeg

[ctuls]

Hi All

First, apologies for the late reply. Getting everything in order took time and I have definitely gotten myself into a situation over here and trying to figure out the best next steps. I will try to breakout the updates into sections:

As a refresher the engine has 80k miles and has been sitting for the past 5 months. I finished resealing the upper oil pan gasket. The lower oil pan and oil pump are currently off the engine.

---

A. Borescope of the 12 cylinders on m70:

Dropbox for videos: https://www.dropbox.com/sh/fz7gn1p4b...qZghHFnja?dl=0

Summary of condition:

1. All combustion chambers and piston tops seem to be fairly carboned up, except for two pistons that have less carbon than others
2. The bores on 10/12 look good
3. Cylinder 10 seems to have a long mark in the bore (depth unclear)
4. Cylinder 11 seems to have a minot mark in bore (depth unclear)

---

B: Leakdown testing:

Tool used: OTC 5609 Leakdown tester with M14 fitting

This is where things get interesting and I am not sure if I have inflicted any damage in the process . Here goes the story:

My general process has been to bring a cylinder to TDC, while observing via borescope. Attach leakdown test hose, run test at 100psi and note down leakage.

1. I started with Cylinder 1 and planned to go in order of M70s firing order 1-7-5-11-3-9-6-12-2-8-4-10
2. I got ~17% leakage on Cylinder 1 which I believe is from rings
3. I got ~ 2% on Cylinder 7
4. I got ~ 8% on Cylinder 5 which I believe is from rings
5. I got ~ 16% on Cylinder 11 which I believe is from rings

Now here is where issues really started coming in

While Cylinder 11 was pressurized, I accidentally knocked the wrench that was on the crank bolt backwards causing the pressure to spin the engine counter clockwise (backwards) I am guessing half a revolution. I read that this can cause timing to slip, so I decided to recheck leakage on 1,7,5 and 11. I rotated the engine clockwise multiple times (assuming I am standing infront of the vehicle facing it) and I didnt feel any issues.

To my dismay all 4 cylinders (1,7,5 and 11) had leakage ~60% now with air also leaking out of the intakes.

I suspected I have thrown the timing off so I used shogun's website to get the dimensions to CAD and get lasercut two cam locking plates from sendcutsend.com out of 6061 aluminum and got the CTA 2890 locking pin.

Now with the valvecovers off, I was able to check timing with the locking pins and plates. I was hoping the timing off was the cause of the issues but it seems that the timing is spot on both banks. Not sure where to go next I decided to leakdown test all the cylinders.

Before this next set of leakdown test I also sprayed Sta-bil fogging oil in all cylinders to maintain ring and wall lubrication.

Results:

1. Cylinder 1: ~60% leaking from intake and crank case
2. Cylinder 7: ~60% leaking from intake and crank case
3. Cylinder 5: ~60% leaking from intake and crank case
4. Cylinder 11: ~60% leaking from intake and crank case
5. Cylinder 3: <5%
6. Cylinder 9: <5%
7. Cylinder 6: <5%
8. Cylinder 12: <5%
9. Cylinder 2: ~12%
10. Cylinder 8: <5%
11. Cylinder 4: <5% some leak from intake
12. Cylinder 10: <5%

Saddened by the results I decided to do some more investigating and problem solving:

• My first hypothesis was the hydraulic lifter somehow is over extended holding the valve slightly open.

- I removed the rocker from Cylinder 1 and retried the leakdown test with still high leakage from intake (using this tool)
- I spent time pushing the valve down assuming it is stuck and needs a little movement to return. No changes in leakage
- I also sprayed it with penetrating oil and moved it after sitting for an hr or two - No changes in leakage

• My thought now was to see how a known "good" intake valve of cylinder 3 (<5% Leakage) moved and performed. So I removed the rocker of that valve and moved it down. I would say it felt a little smoother than intake valve on cylinder 1

- After putting the rocker back in on intake of cylinder 3, I gave it another leakdown test and this time it also had high leakage from intake showing ~60%
- I double checked everything was correct so I rotated the engine a bunch of times and redid the leakdown test and now it came closer to ~15%, with a little leakage from the intake valve

I was surprised that my removing and reinstalling the rocker for cylinder 3 can change the results of the leakdown test!

Now I am trying to figure out what to do next. I have a couple of theories:

1. In going counter clockwise by mistake I bent intake valve of 1, 7, 5 and 11

Factors in support of theory:
- I was on cylinder 11 when it spun backwards and given the firing order it would bend 1, 7 and 5 as they also have high intake leakage

Factors against support of theory:
- I have checked multiple times and I cannot see any evidence of valve kissing the piston on the piston tops of 1, 7, 5 and 11. With the amount of carbon on them I would imagine it would have been a pretty visible mark (although I could be wrong)
- The timing on the engine is still correct

2. A piece of carbon is preventing intake of cylinder 1 from fully closing

Factors in support of theory:
- There is high amount of carbon in the cylinders so it is possible

Factors against support of theory:
- It wouldnt explain why 7, 5 and 11 which are next in the firing order have same fate

2. The engine just needs to be run and heat up to reset things

Factors in support of theory:
- The change in leakage of cylinder 3 when just removing and putting back the rocker, creating leak from intake valve. And then leak reducing after rotating a bunch of times

Factors against support of theory:
-

Would really appreciate any guidance from the experienced people here. I would like to keep pulling the heads as one of the last options. Its crazy how a "while you are in there" to fix the brakebooster pentosin leak turned into this lol

[dragon850]

Almost 100% its the carbon preventing the valve from fully closing.

[ctuls]

Thank you!

Do you recommended way of cleaning it?

I have Sea-foam intake spray which I am planning on spraying on the valve. I am also considering using a heat gun to heat it up to ~400F before spraying to help the chemical

[TTTXGreg]

Thank you!

Do you recommended way of cleaning it?

I have Sea-foam intake spray which I am planning on spraying on the valve. I am also considering using a heat gun to heat it up to ~400F before spraying to help the chemical

Personally prefer Techron in gas once you have it all put together and run it.

[ctuls]

@dragon850 - you were on the money it was carbon preventing the valves from closing.

Here is what I decided to do to fix that:

1. Find the leaking valve using the leakdown tester
2. Remove the intake rocker arm for that cylinder (helps later extend the valve more)
3. Soak it by pouring some seafoam into the intake (my manifolds were off). Hope was to soften the carbon.
4. I took the thinnest nylon bristle brush from this set and forced open the valve using the valve spring compressor tool when the cylinder was at BDC and cleaned around the valve seat.
5. I then while holding open the valve sprayed more seafoam on the back of the valve to wash off anything.
6. I then while fully extending the valve allowed it to slam shut under spring pressure a bunch of times.
7. Test for leaks with the leakdown tester

I had to do the above a couple of times for 2 of the 4 offending cylinders

---

For another experiment (I cant help myself) I decided to do a piston soak using ACDelco 10-3015 Top Engine Cleaner.

For this I placed the spark plugs into each cylinder and poured roughly equal amount in each cylinder through the intake and let it sit for about 8-9 days while I was traveling. I later then used a shop vac with a 1/4 inch OD line to suck out any remaining fluid for the cylinders that had them.

From my initial impressions on some cylinders it really helped clean things up. Keep in mind before they were completely black

PHO00040.JPGPHO00021.JPGPHO00024.JPGPHO00034.JPGPHO00027.JPG

Now I just need to hope that this hasnt damaged anything and figure out what those white looking things in the last image are