Leak Down Test (Don't Laugh!!)

You mentioned there was 12k miles on the bore. So I ASSUME the cylinders/pistons/rings were untouched during the head replacement. Is that correct? If so, did it smoke BEFORE you removed/replaced the head? If the answer is "no," was anything BUT the head changed? The tests indicate there are no issues with the head gasket or valves/seats but the seals remain a possibility and the fact that it doesn't start smoking until the engine has been running a while makes me AGAIN think about the rocker boxes being unable to drain oil as fast as it arrives. BUT...you said you checked and that's not happening.

I'm of the same opinion as Jim re stopping the oil flow to the head and I would be hesitant to do it. IMO, it seems to me you would have to wait at least 5-6 minutes and I think that's too long. Have you tried leaving the rocker cover off - yes it will be messy - and just observing the rocker box for drainage? I did extensive experiments on this some years back and, as noted the spindles facing the wrong way will definitely fill the boxes/submerge the valve guides/overwhelm the seals and it takes some minutes for that to occur. Of course, a plugged drain hole in the box will do the same thing. I know you said you checked all this but it fits the time frame and the smoking issue. Have you tried starting the bike, waiting for it to smoke, shutting it off, waiting for 4-5 minutes and starting it again to see if it smokes immediately or takes another 3 minutes to begin smoking?

Jim mentioned porosity and, if there was some porosity or crack between the rocker box area and the intake port, oil would, of course be pulled through when the engine was running. That would also take some time to occur from a start if the bike hadn't been running for a while.

How's the oil level in the tank? If too full, oil could be drawn into the air filter box/into the engine. BUT if that's the case, one would expect oil in both cylinders.

Forget all this talk about riding it hard , hoping it all clears up. Do the rocker feed blockage test.

MexicoMike said:

You mentioned there was 12k miles on the bore. So I ASSUME the cylinders/pistons/rings were untouched during the head replacement. Is that correct? If so, did it smoke BEFORE you removed/replaced the head? If the answer is "no," was anything BUT the head changed? The tests indicate there are no issues with the head gasket or valves/seats but the seals remain a possibility and the fact that it doesn't start smoking until the engine has been running a while makes me AGAIN think about the rocker boxes being unable to drain oil as fast as it arrives. BUT...you said you checked and that's not happening.

I'm of the same opinion as Jim re stopping the oil flow to the head and I would be hesitant to do it. IMO, it seems to me you would have to wait at least 5-6 minutes and I think that's too long. Have you tried leaving the rocker cover off - yes it will be messy - and just observing the rocker box for drainage? I did extensive experiments on this some years back and, as noted the spindles facing the wrong way will definitely fill the boxes/submerge the valve guides/overwhelm the seals and it takes some minutes for that to occur. Of course, a plugged drain hole in the box will do the same thing. I know you said you checked all this but it fits the time frame and the smoking issue. Have you tried starting the bike, waiting for it to smoke, shutting it off, waiting for 4-5 minutes and starting it again to see if it smokes immediately or takes another 3 minutes to begin smoking?

Jim mentioned porosity and, if there was some porosity or crack between the rocker box area and the intake port, oil would, of course be pulled through when the engine was running. That would also take some time to occur from a start if the bike hadn't been running for a while.

How's the oil level in the tank? If too full, oil could be drawn into the air filter box/into the engine. BUT if that's the case, one would expect oil in both cylinders.

Click to expand...

1. Cylinders/pistons/ring were not touched

2. Did not smoke before, apart from the time a valve seal came loose, which I fixed

3. Head was the only thing changed

4. When I put the head on during the first startup I left the rocker box covers off to observe the oil level, everything was fine, nothing filled up & drainage was good.

5. I have not started the bike again after waiting 4-5 mins to see if it smoke immediately or takes another 3mins to smoke

6. Oil level is low

7. I'm assured that Jim has checked this head twice, once before the rebuilt it & once again after I sent it back to him.

gosh that is so refreshing to read as not me this time. I had oil tight non smoking factory Combat, after a number of factory bomb parts rebuilds, as long as didn't give much throttle or go over 60's mph. It had a few of the issues listed I found solved, to finally realize had to split cases to clear internal oil passage that flowed fine till heat swollen allowed swarft to pile up and wet sump more that the low down breather secondary return path could keep ahead of. I broke a ring, lost a circlip, (weeks to get friends enough to flip it over, just in case in cases but it wasn't) and then barrel bottom bores off, when wife missed a zip tie w/o knowing it, over 2 yr ago, but too many other fires to recover that hobby horse so far. Ugh, suppose ya don't find anything to fix and passes all tests, then what?

I'd call it unlikely but it is possible that a ring(s) may have rusted/frozen in the barrel and broke when the engine was kicked over. But that should have shown up in the comp/leak tests. Frankly, based on the info, it sounds like what's happening can't be happening! But since it is, obviously we are missing something.

I know several people have mentioned just taking it out and running the cr@p out of it. That method sometimes works for carbon buildup/associated sparkplug misfiring but I can't imagine it would do anything useful in this situation but it can't hurt (other than the embarrassment of all the smoke!) The possibility that the muffler on that side has a lot of oil that smokes when it gets warm? Well, maybe initially but it would stop after a while unless fresh oil is being added...and how did the oil get in there in the first place since the engine was NOT smoking before the head was replaced. But again, sure can't hurt!

You mentioned, "There is a bit of 'gurgling' from the breather tube in the oil tank." I would expect ring blow-by (from the leakdown test) to pass easily out of the engine via the crankcase vent since there would be less resistance to the airflow. IOW, you should hear hissing there rather than from the oil tank. Are you sure the crankcase is venting properly? Then again, if it wasn't, I would expect both cylinders to be ingesting/burning oil unless maybe one set of rings is doing the job much better than the other set.

Assuming the "run the cr@p out of it" doesn't help, I would just bite the bullet and pull it apart. It seems logical to me that it's related to the head or the installation process since the problem didn't exist prior to the new head. But whatever the problem is, I don't see any way to resolve it without pulling it back apart.

Did you, by any chance repeat, the comp test (180 PSI seems awfully high) and the leakdown test? I have done a LOT of leakdown tests and I have never seen any "used" engine show that low - looks like around 2%. Frankly, very few newly rebuilt, blueprinted engines by excellent shops achieve 2%. I would expect an engine with 12k miles on it to be in the 10-15% range and higher wouldn't be unusual at all.

I mention the above because the comp/leak test results eliminate several of the "usual suspects." So maybe the tests should be retested...just to be sure!

A basically agree with Mexicomike.

Sometimes, especially when it’s our own bike, we can think something mystical is going on because we KNOW that x, y and z are all fine.

But at the end of the day, it’s only an engine and what’s happening can’t be cos of black magic! There is a logical, practical, physical reason for this. You just haven’t found it yet!

As Mike says, it could be as simple as the absorption material in your muffler has soaked up loads of oil and that’s whats now burning off (this has happened to me before).

It could be a stuck / gummed up ring. Or something else really minor.

So, although it’s a long shot, giving it a good long thrashing will at lease confirm or reject the above causes.

Gotta be worth a try I’d say.

hobot said:

gosh that is so refreshing to read as not me this time. I had oil tight non smoking factory Combat, after a number of factory bomb parts rebuilds, as long as didn't give much throttle or go over 60's mph. It had a few of the issues listed I found solved, to finally realize had to split cases to clear internal oil passage that flowed fine till heat swollen allowed swarft to pile up and wet sump more that the low down breather secondary return path could keep ahead of. I broke a ring, lost a circlip, (weeks to get friends enough to flip it over, just in case in cases but it wasn't) and then barrel bottom bores off, when wife missed a zip tie w/o knowing it, over 2 yr ago, but too many other fires to recover that hobby horse so far. Ugh, suppose ya don't find anything to fix and passes all tests, then what?

Click to expand...

Hopefully I won't have to go through all the 'pain' you went through

MexicoMike & Fast Eddie,

I really appreciate all the thought you are putting into this

I'm quite philosophical about finding what the issue is, I'll get there . . . . . . . eventually

It looks like I have the following options:

1. Bite the bullet & strip down to the barrels & check ring/bore spec (popular choice, less chance of cocking up!!)

2. Give the bike a good run while contributing to global warming in hope of 'freeing' up a stuck ring (unlikely but possible)

3. Disconnect the oil line to the head to see if it's a top or bottom problem (jury's out on this one!!)

3. Re-do some of my tests to ensure the results I got are accurate (worth a try). About this, just in case I'm not doing the leak test correctly, this is what I'm doing:

Ensure piston at TDC (both valves closed on the side testing!)
Cold engine
Connect leak down tester, turn air intake control on tester so the 2nd meter measuring leakage is at zero. Wait & see how far it drops & stays there. Listen for any 'hissing' sound around the head.

Rings
Check they are correct in everyway as from my experience posted here on the site, the oil rings were the issue not compression as I had plenty, did all the things you have done, checked piston's, cracked heads valve guides etc, was sent 3 sets of rings of oil control rings before getting a correct set, and now all good, just my two bobs worth.
Burgs

Burgs said:

Rings
Check they are correct in everyway as from my experience posted here on the site, the oil rings were the issue not compression as I had plenty, did all the things you have done, checked piston's, cracked heads valve guides etc, was sent 3 sets of rings of oil control rings before getting a correct set, and now all good, just my two bobs worth.
Burgs

Click to expand...

Really appreciate your real world experience.

This matches what I feel is going on, I think it's my oil ring is stuck or broken. I'm conscious I don't just find 'facts' that fit my theory, hence the reason for asking the collective brain of AccessNorton.

Interesting about the oil control rings, when you say you had to get 3 sets before getting a correct set, what was the parameter(s) of correctness? Was it ring gap?

Hi Click
The expanders were the problem, I eventually put the original expanders in a new set of rings.
The newer expanders weren't exerting enough pressure onto the rings in the bore.
With just the oil rings (with the expanders) fitted to the pistons, test the weight required to move the pistons in the bore, from memory Hastings said around 13lb force, my rings basically had no resistance, and slipped through with a light touch of my finger, I questioned Hastings about the weight as that seemed a lot and they replied that it was correct.
I still have a set of new rings to try, but I was running out of time and fitted the original expanders to the new rings, the force then required was about 13lb, all good now.
Things I measured previously was the ring gaps, piston ring groove depth, ring fit in the groove, piston dimensions, bore for taper etc and anything else I could measure, all in spec, except what Hastings said about the force exerted on the oil rings.
Also did all the head things like new guides, Teflon seals, crack testing etc, these made no difference other than I know I have now done all that.

Burgs

While it seems unlikely to be oil soaked into the muffler, I'd probably take the muffler off and run the bike just to confirm before getting inside. The exhaust will be coming off anyway. It would be a bit of a bad joke to tear the motor all the way down and not find anything because it actually was the muffler.

Burgs said:

Rings
Check they are correct in everyway as from my experience posted here on the site, the oil rings were the issue not compression as I had plenty, did all the things you have done, checked piston's, cracked heads valve guides etc, was sent 3 sets of rings of oil control rings before getting a correct set, and now all good, just my two bobs worth.
Burgs

Click to expand...

What was "correct" and not "correct" about them?

I think he do what hastings advised about the 13lb pressure on oil rings , then we could refer to the problem evocated while ago regarding some who trimed their oil ring scraper to fit .........my two cents , but may be I am wrong !!!

Re; “I was having an oil burning issue which seemed to be a valve seal. I did the rope trick & replaced the valve seal with the head in situ & it seemed to solve the problem but only for a short while. I did the rope trick procedure again but dropped a collet down the pushrod tunnel!! After 4 days of fishing around I had no choice but to take the head off. While it was off I thought what the heck I'll get the head freshened up. Jim was up to his tonsils so I sent it to a well known cylinder head shop in the UK. I had a few issues with the head after I got it back, it looked like they had installed the rocker arm shafts cold as they were very loose in the head. I ran the bike for a bit like this but always felt the bike deserved a better job done on the head.”

Here’s someone I wouldn’t trust with my c/head! For all you know they might have fitted the rocker shafts in the wrong way round resulting in excess oil in the rocker box?

Yes, rocker shafts might be loose in the head from a bad cold install. They should be tight in place. I'd take off the rocker covers and with a large screwdriver see if they rotate or move too easily/with slop to confirm that. Easily done. One or two could have rotated on the right side so start there.
Also you mentioned replacing a valve seal . Was it on the right side? It could have popped off again due to a poorly cut ridge for it's placement over the intake guide.

From the discription of your timeline which you listed above, it sounds like it's your head gasket not sealing properly between the cylinder and the pushrod tunnel. Since you didn't have some injury event prior to the problem, I would think everything below the head has not changed since you sent the head out.

I would see if a flame ring style head gasket for your 920 is available.

As a note of comparision to my previous comment about the scoring of my barrels when a circlip popped out. I was doing about 60mph and when it dislodged there was loud "POP", and a puff of blue white smoke, so there was no missing the failure event. If you had no similar event, I would bet you're having a devil of a time getting the head gasket to seal and nothing more... (that's just my guess)

One thing to think about when doing a leak down test is to check at TDC,MDC and BDC as if there is cylinder wear at the middle or bottom you will never detect it measuring at TDC only.

Craig

Someone has probably said this earlier. Are all the rocker shafts in the correct orientation and are not the scrolled type.

One quick check for valve guide leak is to remove the plugs and shine bright pen torch down the pug hole turn the motor over and you'll see the valve condition. If the inlet valve and d stem are covered with oil there's a good chance it's seal or guide to head problem. You can see the exhaust valve too but it's better to remove the pipe and you'll easily see any issues there.
Don't forget it's usually the last thing you did.
Dave

Most of these theories are valid but anyway you look at it the head will have to come off. If you find a leaking inwards head gasket on the right side then you might consider leaving the barrels in place.