1 Cylinder low compression need help

[i_build]

I put on about 400 miles after building an M20 with an E bottom end and I head. Rebuilt the lower end with new bearings and rings and top end needed new valves and stems... machine shop tested the head... used ARP fasteners to put it in.

I didn't realize that the 3rd cylinder from the back of the engines valves were too tight and she started to develop a miss fire and smoke from the exhaust under boost. Just re-adjusted the valves in hopes that would help but no go.

Compression test was even across all cylinders and then 30psi less on this 1 cylinder plug was black compared to the others.

Leak down test showed no air coming from the crank case but air coming out of the valve cover. At TDC for this cylinder there is air coming from those valves.

I used a bore scope and can't see any collision damage on the flat top E pistons but for the life of me I can't get the scope pointed up to see the valves. Is it possible since they never really closed that I just have a ton of deposits on them and they aren't sealing?

OR

Does this mean I HAVE to pull the head?

Considering that it's the I head with E pistons I couldn't see collision being an issue with misadjusted valves... but could that have happened? I hope not because I paid a nice amount of money for these new valves... Could I have messed up seating valve a stem seal?

Any advice as to how to work this issue appreciated?

Thanks in advance.

[TobyB]

no air coming from the crank case but air coming out of the valve cover.

huh? the crankcase and valve cover are connected by the bitch tube...

If you're hearing air from the tailpipe, it's the exhaust valve, and 'under boost' suggests a burnt exhaust
valve, as they're usually the first things to give up when you go lean.
If you're NOT, and also not from the intake either, then it's ring seal.

But.

On ePay for not too much money are borescopes with a 'side looking' camera- a must for every N14 MINI owner,
since it's possible to get a look at the valves with them. That might be a next step to see if you've
lost a chunk of valve. 30 psi down in a compression test, however, is pretty minimal for valve damage...
did you try oil in the low cylinder to see if that made a difference?

some ideas,
t

[i_build]

When I did the leak down with the valve cover off I felt the air coming out from the exhaust valve spring. I even placed a piece of paper towel over the bitch tube inlet to the head and it didn't move. I pulled the head and set it up with the valves closed and filled the chamber with acetone and not 1 drop made it through and its been 2 hours plus now so I am confused as heck... I could have sworn the valves were closed because I felt both the rockers move but it makes no sense. I lapped the seats and tested the same way with acetone before the install and no leaks... so I am 100% confused here. I do know that whenever I boosted I got smoke from the tail pipe and from the valve cover vent tube that I ran under the frame and I do know that this cylinder was much lower in the compression test than the others but visually it doesn't look like the valves were bent. They seem to seat fine into the head and they hold the acetone. Now that I have the head off is there any way to tell if my rings are shot? Like I mentioned that 1 plug was black... how can I check the integrity of the rings with the head off now? I still have my M20B25 lower end and I am thinking of just biting the bullet and building that up... but its a shame cause I did the bearings and the rings on the other E lower end... but I guess I may have messed that up... Really confused now.

[McGyver]

It sounds like something went wrong with one of your tests or you have a cracked head.

If your valves are sealing to hold acetone, then air isn't getting past them. If air was to get past them during a leakdown, the path of least resistance is out the exhaust or intake. It wouldn't make sense for the air to push up past the valve guide and valve stem seal directly into the head. A cracked head into the intake/exhaust runner would still flow out the intake/exhaust.

You said you pulled the head and lapped the valves. Did you see a burnt exhaust valve or excessive carbon buildup?

You said the valves were too tight. Does that mean the valve guides were too tight on the valve stem, or you didn't leave enough clearance between the cam and rockers?

If the valve clearance (cam/rocker) was too tight, is there a chance that the cam was slightly opening one of the valves?

Now that you have the head off, do you see piston to valve damage?

Is it possible that your misfire is just from a bad plug or plug wire?

Assuming all your valves look good, why not reinstall the head and see what you get. The bottom end might be fine. Make sure to loosen the rockers before installing the head. Then adjust your valves once the head is torqued down. Take your time to get the engine to TDC and make sure the gap is correct. A little loose is better than a little tight.

[McGyver]

Also, here's a DIY for making a trigger to turn over the starter from the engine bay. It makes it really easy to get the cylinders to TDC for a valve adjustment.

DIY - Making a Remote Starter Trigger - R3VLimited Forums

[i_build]

It sounds like something went wrong with one of your tests or you have a cracked head.

If your valves are sealing to hold acetone, then air isn't getting past them. If air was to get past them during a leakdown, the path of least resistance is out the exhaust or intake. It wouldn't make sense for the air to push up past the valve guide and valve stem seal directly into the head. A cracked head into the intake/exhaust runner would still flow out the intake/exhaust.

You said you pulled the head and lapped the valves. Did you see a burnt exhaust valve or excessive carbon buildup?

You said the valves were too tight. Does that mean the valve guides were too tight on the valve stem, or you didn't leave enough clearance between the cam and rockers?

If the valve clearance (cam/rocker) was too tight, is there a chance that the cam was slightly opening one of the valves?

Now that you have the head off, do you see piston to valve damage?

Is it possible that your misfire is just from a bad plug or plug wire?

Assuming all your valves look good, why not reinstall the head and see what you get. The bottom end might be fine. Make sure to loosen the rockers before installing the head. Then adjust your valves once the head is torqued down. Take your time to get the engine to TDC and make sure the gap is correct. A little loose is better than a little tight.

I lapped the valves because I was replacing them due to a timing belt skip at startup the last time I installed the head over a year ago. Other than the plug being black and smoke coming from both the exhaust and vent on the valve cover after boost... I did not see any major build up of carbon or oil because It's been about 4-500 miles after my first rebuild attempt.

When I mentioned tight I was referring to the adjustment of the eccentric. The rocker even at the lowest point on the cam lobe had no free play and that I would assume would have left that valve slightly open even when it was supposed to be closed. I did readjust it properly afterward and took it for about a 50 mile drive and it was still smoking after boost from both the valve cover vent and exhaust and I mean embarrassing smoke. That was when I did the compression and leak down test and saw the discrepancy on this one cylinder... and I repeated that test 2 times and one other the following day to make sure the fatigue factor wasn't the problem... Then I pulled the head... Odd thing also was that I did the same leak down pressure on all the cylinders and I did feel some air that came up from all the exhaust valves... not sure if that is to be expected.

I do not see any signs of collision on the pistons or valves... they all "seem" to open and close just fine... and I repeated the acetone test this morning on that one cylinders valves and I see no leaks... I also took alcohol and measured 2 equal amounts and poured it down the bore of the low compression cylinder as well as the same amount in a cylinder that had high compression... AND... the one that had high compression drained out before the one with the low compression... so I would assume that means the rings are as good in the low compression cylinder as they are on the good compression cylinder... I just poured in enough alcohol to be 1 inch from the top end of both the cylinders and both took over 10 minutes to even reach the top of the cylinder but the higher compression one drained slightly faster. Cross hatching is still in place on all cylinders.

Not sure about the bad plug / wire issue... I was thinking that would have not impacted the compression or leak down test... I was really trying to figure out where all the smoke was coming from and suspected the low compression on this 1 cylinder... I took my DP off to check the back of the turbo and it was not oil soaked.... it looked dry... So I don't think it would be coming from Turbo seals...

I noticed that the HG I used did have the metal part that goes around the oil passage and that passage is closest to the cylinder that was low compression... it did not look like it was compromised... but I am reaching on this... I dont want to reassemble and have the same issue... and I don't want to rebuild the original M20B25 block and find out I have a head issue and the E block was fine (with new bearing and rings already in it)... I did have the head checked before I installed it and the machine shop said they had not seen a B25 head in a long time that was in this good condition... but I know things happen and I did put 500 miles on it since then. I am using ARP fasteners for the head and I didn't have any detonation or over boost.

I like the tip about adjusting the rockers after the head is in place and leaving them loose... I think that was where I messed up... after I replaced the valves I adjusted them on the bench and it makes perfect sense that was where I messed up. Will acetone test the rest of the valves and provided they pass buy a new HG and give her a go again.. I think the last HG was a FELPRO should I avoid that one?

[McGyver]

I’m wondering if you have multiple issues showing up at the same time.

Other than the plug being black and smoke coming from both the exhaust and vent on the valve cover after boost... I did not see any major build up of carbon or oil because It's been about 4-500 miles after my first rebuild attempt.

What are your compression numbers? Could this be blowby into the crank case, causing oil mist to be pushed into the intake, and you to burn oil? You said you only had 4-500 miles on the engine with new rings, did you seat the rings?

The rocker even at the lowest point on the cam lobe had no free play and that I would assume would have left that valve slightly open even when it was supposed to be closed…
… after I replaced the valves I adjusted them on the bench and it makes perfect sense that was where I messed up.
…I think the last HG was a FELPRO should I avoid that one?

You said the valves don’t leak, but having them slightly open all the time may have caused some problems. Perhaps you should give them all a quick lap for the heck of it.

You have to adjust the valves once the head is torqued to the engine because the casting will move. Honestly, you should probably re-adjust the valves after the engine has gone through a few heat cycles to relax into place.

I think the current consensus is to use a Corteco HG.

Not sure about the bad plug / wire issue...
…I took my DP off to check the back of the turbo and it was not oil soaked

The black plug could be an entirely different issue. Check the plug in another cylinder, inspect the ignition cap and rotor (sand off corrosion). Check your plug wires. Perhaps it’s a leaking fuel injector that’s making your cylinder rich, you could move it around to a different bank (1-3 vs 4-6). Try moving wires/sparkplug/injector one at a time to isolate the issue.

[i_build]

I’m wondering if you have multiple issues showing up at the same time.

What are your compression numbers? Could this be blowby into the crank case, causing oil mist to be pushed into the intake, and you to burn oil? You said you only had 4-500 miles on the engine with new rings, did you seat the rings?

This is a dumb question and will show the fact this is my first rebuild... I did gap the rings and I did not get into boost until after about 300 miles of driving on highway and on local roads and at that time when I got into boost I didn't have any smoke it started just recently.... when you say seat the rings... what exactly does that mean? I did make sure that they were gapped correctly and I clocked them at the time as well... just not sure what seating the rings means and that may be the reason why I have my issue and want to understand.

My numbers were 130ish across the board for all cylinders except this one... this one maxed out at 70... I don't know for sure but I assumed that 130ish was ok for the E bottom end and I top end considering that combo was supposed to be lower in compression... It ran and idled well but as of late developed a slight miss and the smoke that we are trying to track down... never stalled... did not smoke at idle... and the only issue was I felt like after I boosted I hit a smoke screen button and the people behind me got the brunt of it... then at a light the tube I ran from the valve cover under the car (open vented) would pour out smoke from the side... car is beautiful and I get thumbs up an comments all the time... then feel embarrassed after it does this. I had it for about 13 years and converted from Auto to Manual and then installed Megasquirt and learned it... then went boosted for about 5 years till the original I engine got tired.. then decided to try to learn to build a stroker and bought an E engine rebuilt the lower end and bolted on the I head and now here I am with a bunch of problems... being in my late 50's doesn't help much now either.. but my wife and I love the E30 and the attention we get with it.

P.S. I started tearing down the B25 block as well I liked the way that it ran and would rather the higher compression and lower boost TBH.... but even before I start rebuilding it... want to make sure this time around I don't make the same mistakes I apparently made with the E lower end.

Would blow by increase with a high oil level?

[McGyver]

I'm in the middle of my first engine build, its currently still disassembled. Ring gaps and clocking is very important for assembling. Seating the rings, or breaking in the engine, helps to ensure a good seal. Did you give the cylinders a light hone when you had the block apart for the new rings? The original hone marks may have looked good, but you could have had some glazing smooth them out. Here's a couple of articles I found and skimmed:

How to Break-In Your Piston Rings, The Right Way! - Engine Builder Magazine

Engine Break-in: Truth, Lies, and What You Really Need to Know. - Articles - ThumperTalk

130psi seems low, but having one at 70psi is really bad. The compression test should be with a freshly charged battery, throttle body held open, and ideally the air box/intake boot removed.

If you're over filled with oil, it could definitely cause the car to smoke. But we're talking several quarts over. Plenty of race cars run with an extra quart to prevent oil starvation around corners.

[i_build]

I did hone the cylinders well and the cross hatching is still there but I am not sure whether what I am seeing is what is right... I clocked the rings as well as used break in oil and have changed since the first 100 miles... one thing interesting in the first link was how it mentioned running overly rich could possibly cause the rings not to seat properly I guess because of the "wash down" impact of too much fuel. My setup likes to idle at 13.5 AFR so not sure if that was a contributing factor. The link mentioned an AFR of 10 but I would never do that at idle... engine wouldn't like it anyway.

Sorry thing is that during tear down of the original B25 block I remember why I switched years ago... 1 of the pistons is missing a chunk... and there are a few nicks in that bore... so I am not even sure whether that block can survive... but worse case I can use the E block with the I rotating assembly and pistons... everything but that 1 piston and block look pristine... so I would need to source another I piston to rebuild that. Not abandoning the E lower I have now just yet... I do think I was overfilled... but not by several quarts...

When you build an engine that is supposed to be lower in compression (such as with the E flat top pistons and I domed head) would you expect that the compression numbers on a compression test be lower than normal? Including a pic of the suspect cylinder... cross hatching didn't come out to well in the pic but it is there. All the piston tops have the same build up... I'm just not educated enough to know whether the amount of cross hatch is still good enough... The rings look in tact on all...

[i_build]

Here's a better picture of the cross hatching as is now... also a pic of the plugs and how bad that 1 was... and a pic of the valve I suspected but am questioning whether my test was valid. That one plug may have indicated a stuck or leaking injector I guess... that may have not let the rings seat properly washing that cylinder down so I will test that also.

[66Vette]

I think ultimately a leak test is the best way to get your answer. One method I have used, if I have the head off, is to make a block-off plate with an air fitting. This will allow you to isolate your leak. I use a thick plate of aluminum that will cover one cylinder and the surrounding bolt holes. Drill holes in the plate to match the bolt holes in the block with the air fitting in the center of the plate. Then add a thin piece of rubber as a gasket and bolt the plate in place. Now you can use your leak down tester to check the cylinder itself by connecting to the air fitting. The nice thing about this approach is you can reverse the plate and bolt it to the head and run a leak down on the head alone. Now you have a way to separate and measure which part is the problem.

I am not an M20 expert so don't know if the head bolt-pattern repeats for each cylinder. If it does, you only need to drill one set of holes in your plate and you can repeat the test for all the cylinders. Its a great way to definitively measure valve and seal ring seal separately.

[i_build]

Ordered an ELRING HG just to bolt the head back on and test again. Not sure whether the rings seated right or not during break in. Will fill her with the right amount of oil after reassembly and I cleaned out the injectors and took some emery cloth to the dizzy and rotor... I'll run her for a bit no more than 7 psi boost and see if she settles in... and hopefully that one cylinders rings seat if that is the compression issue on that one cylinder.

Really discouraged now cause I see that one of the cylinder bores on my extra block really doesn't look good either... was thinking about rebuilding that block as a backup... and now I saw one piston had damage which I see now damaged the cylinder bore... is it ridiculous to even try to hone that out? Don't know whether it's M50 / 52 swap time or not...