Leak Down Test (Don't Laugh!!)

Status
Not open for further replies.
OK, started 920 from cold, took 3 minutes for smoke to build up.

Just checked the spark plug, I could wipe oil off the face of the spark plug.

Here's some phone video after 4 minutes from startup:

 
Last edited:
Wow...that's a LOT of smoke. Frankly, if it was me I'd just bite the bullet and pull the head/barrels and basically "start over." I originally said valve seals but that's an awful lot of smoke for seals unless they are totally missing AND the valve guide/valve stem clearance is really excessive. It could be a poor cylinder wall/ring interface due to improper finish on the cylinder causing the rings to have never seated properly.

To be honest, if I saw an engine doing that, my first reaction would be to just consider it clapped out and needing a rebuild. Was anything other than the head redone? If so, is it possible that the wrong size rings were used? IOW, if perhaps the cylinder was bored at some time in the past to .010, .020 or whatever oversize but the rings were not of the corresponding oversize? Or, as I said, maybe the cylinder wall was not properly finished for the new rings. The proper bore finish is related to the composition of the rings. IOW, cast iron rings require a different bore finish than moly rings. OR, is it possible that new rings were installed with no bore refinishing? The same thing will happen - poor oil control.

The part that is most interesting to me is that you stated that the leak down and the comp test show good results which would then indicate that cylinder sealing, which includes the head gasket, valves (to valve seats) and the piston rings, is good. That's why my initial reaction was valve seals/guides since that is not "checked" by those tests.

In any case, UNLESS you check and find the valve seals missing(!) I'd just tear it down and rebuild it - checking to verify the cylinder diameter and ensuring the correct size rings are purchased and ensuring the bores have a suitable finish for the new rings. Off the top of my head, I can't see how cracks/porosity in the head can cause the problem because that would show up in the two tests unless the cracks/porosity are in the valve box which would allow oil into the combustion chamber when the valve opens but the tests would not show that, just as they would not show bad valve seals/guides.

Good Luck!
 
Hi, I was hoping you did not do the copper wire around pushrod tunnels , with pliobond , so ...but you did ! I have a 920 built by a mix of Pete Lovell and Les (who did what , ???), and yes it was smoking , but just a bit a the start, and far less than yours, after putting this engine off the bike for years , I had it apart last summer , checked everything , and do the thin wire with new head gasket and gasgacinch (no pliobond available in France!!), and that time tho smoking a tiny bit , everything was ok , I know those 920 barrels had this reputation, so I think I am ok now .....sorry if I do not help you so more but I think you have to lift the barrel again and check rings , and clearances !
 
MexicoMike said:
Wow...that's a LOT of smoke. Frankly, if it was me I'd just bite the bullet and pull the head/barrels and basically "start over." I originally said valve seals but that's an awful lot of smoke for seals unless they are totally missing AND the valve guide/valve stem clearance is really excessive. It could be a poor cylinder wall/ring interface due to improper finish on the cylinder causing the rings to have never seated properly.

To be honest, if I saw an engine doing that, my first reaction would be to just consider it clapped out and needing a rebuild. Was anything other than the head redone? If so, is it possible that the wrong size rings were used? IOW, if perhaps the cylinder was bored at some time in the past to .010, .020 or whatever oversize but the rings were not of the corresponding oversize? Or, as I said, maybe the cylinder wall was not properly finished for the new rings. The proper bore finish is related to the composition of the rings. IOW, cast iron rings require a different bore finish than moly rings. OR, is it possible that new rings were installed with no bore refinishing? The same thing will happen - poor oil control.

The part that is most interesting to me is that you stated that the leak down and the comp test show good results which would then indicate that cylinder sealing, which includes the head gasket, valves (to valve seats) and the piston rings, is good. That's why my initial reaction was valve seals/guides since that is not "checked" by those tests.

In any case, UNLESS you check and find the valve seals missing(!) I'd just tear it down and rebuild it - checking to verify the cylinder diameter and ensuring the correct size rings are purchased and ensuring the bores have a suitable finish for the new rings. Off the top of my head, I can't see how cracks/porosity in the head can cause the problem because that would show up in the two tests unless the cracks/porosity are in the valve box which would allow oil into the combustion chamber when the valve opens but the tests would not show that, just as they would not show bad valve seals/guides.

Good Luck!
Click to expand...

You can now see why I was leaning towards the oil ring. As far as I'm aware you can still have good ring to bore seal with the two top rings but if the oil ring is not working correctly it can allow oil to enter the combustion chamber.

The bike was converted to a 920 12K miles ago and I have not touched the barrels/pistons/rings myself since then.
 
marinatlas said:
Hi, I was hoping you did not do the copper wire around pushrod tunnels , with pliobond , so ...but you did ! I have a 920 built by a mix of Pete Lovell and Les (who did what , ???), and yes it was smoking , but just a bit a the start, and far less than yours, after putting this engine off the bike for years , I had it apart last summer , checked everything , and do the thin wire with new head gasket and gasgacinch (no pliobond available in France!!), and that time tho smoking a tiny bit , everything was ok , I know those 920 barrels had this reputation, so I think I am ok now .....sorry if I do not help you so more but I think you have to lift the barrel again and check rings , and clearances !
Click to expand...

Appreciate the reply :)

So far pulling the barrels is top of the list :-(

It would make a great James Bond bike, they'ed never see you through the smoke screen :)

Hate having to take everything apart again!! I'll let this sit in my brain for a while & hopefully 'it' will accept the logic!!
 
Head checked, rings good, compression test done then there is one area I would look at next - a barrel shaped bore. New rings could have masked this issue for a while. Compression test can't detect it. Usually incorrectly honed barrel causes this, some are so bad that the first pass on re-bore will miss the centre section.
 
Madnorton said:
Head checked, rings good, compression test done then there is one area I would look at next - a barrel shaped bore. New rings could have masked this issue for a while. Compression test can't detect it. Usually incorrectly honed barrel causes this, some are so bad that the first pass on re-bore will miss the centre section.
Click to expand...

New 920 standard liners, pistons & rings were installed 12K miles ago. Also did a leak down test.

Can anybody answer this, if the oil ring was not working could this account for the oil burning in the video?

If it was the oil ring why does it take 3 minutes before I see plooms of smoke?
 
I don't think it's the oil ring - too much smoke at no load. It really looks to me like some sort of bore/ring (all rings) issue. Though, again, I don't understand the comp test/leak down results if there was a bore sealing problem. Leakdown in conjunction with compression tests are usually very good at identifying such things. I would have said they are ALWAYS good but maybe this is one of those odd cases. I just don't see how the two didn't easily show the problem if it's ring/cyl wall/valve seat/head gasket related!

FWIW and apropos of nothing, a compression test by itself is, IMO, 1/2 a test. The leak down is a much better test overall and, in conjunction with compression is, in my experience, nearly infallible! But...perhaps not. ;)
 
I verify that just wet sump splash can over oil bore even good oil ring can't wipe so smokes like that till flushed out. Suppose a broken oil ring could leave enough to smoke on one side only. Leak down tests are not complete w/o checking somewhat down on either side of TDC which is serious task in Commando jug under pressure, soon as .005* off TDC. Its entirely possible some oil return issue only showing up on the less well sealed side but not likely. As stated a few times prior, in for a penny in again all the way.

How's the sump magnet look? Most of it is flake/splinters/nano dust off rings bores and bearings rollers/races. Bore scratches or wear enough to smoke would leave extra. Let us know once in hands again : )
 
I recall reading that if a rocker arm shaft is put in with the bleeder hole facing the wrong way it pumps way too much oil into the top. You might check that.

I also thought that maybe the drain hole for the head is clogged at the base of the barrels where it enters the crankcase causing oil to back up as it's fed into the head. Maybe a blob of silicone went down the hole and is stuck.. I wonder if there's a way to poke that hole with the barrels in place to make sure the hole is clear.

That test where you disconnect the oil feed to the head may tell you if the leak is coming from the head or the piston side, but I wouldn't do it without consulting someone knowledgeable...

And lastly, Pulling the barrels isn't really that big of a deal.
 
hobot said:
I verify that just wet sump splash can over oil bore even good oil ring can't wipe so smokes like that till flushed out. Suppose a broken oil ring could leave enough to smoke on one side only. Leak down tests are not complete w/o checking somewhat down on either side of TDC which is serious task in Commando jug under pressure, soon as .005* off TDC. Its entirely possible some oil return issue only showing up on the less well sealed side but not likely. As stated a few times prior, in for a penny in again all the way.

How's the sump magnet look? Most of it is flake/splinters/nano dust off rings bores and bearings rollers/races. Bore scratches or wear enough to smoke would leave extra. Let us know once in hands again : )
Click to expand...

Thanks hotbot.
The stinker is that it takes 3 minutes for it to start smoking, I also have Jim C's sump breather which shifts any wet sump oil back to the oil take really quickly.

I take the sump magnet out on a regular basis just to check for any 'chunky' bits!!, never seen anything other than a light fuzz.
 
o0norton0o said:
I recall reading that if a rocker arm shaft is put in with the bleeder hole facing the wrong way it pumps way too much oil into the top. You might check that.

I also thought that maybe the drain hole for the head is clogged at the base of the barrels where it enters the crankcase causing oil to back up as it's fed into the head. Maybe a blob of silicone went down the hole and is stuck.. I wonder if there's a way to poke that hole with the barrels in place to make sure the hole is clear.

That test where you disconnect the oil feed to the head may tell you if the leak is coming from the head or the piston side, but I wouldn't do it without consulting someone knowledgeable...

And lastly, Pulling the barrels isn't really that big of a deal.
Click to expand...

Rocker arms checked before I installed the head again just to be sure, holes point the correct way.

Before I put the head on I used wire to poke down the drain hole in the barrel, I also squeezed oil from an oil can down the hole & it flowed fine. I also check the drain holes in the head. I never use silicone sealant on any surface were it might get inside the engine.

When you haven't done something before you just need time to think it through (removing barrels), I'm still thinking it through :)
 
Copper wire around the pushrod tubes is a good way to insure there will be leakage problems at the head gasket.
If you want to prevent leakage there you will need to groove the barrel for copper rings around the bores. Jim
 
You will probably end up pulling the barrels. But I for one would try a prolonged period of thrashing the arse off it first!
 
3 min delay distinctly implies waiting for head pressure to build so prior mentioned reversed spindle or intake seal makes sense to me. Easiest most logical test for that is run some w/o oil to head, which ain't getting any for 3 min anyway duh. IIRC ya said not over flowing in rocker boxes, so seal may be it. I just want to be a pilot as each mechanical task tests my will power to struggle again plus rising risks I'll screw something else up again, like head resealing, after push rod prison puzzle... can't leave till solved.
 
OK Lads, appreciate all the advice.

Few questions to pick your brains about the oil circulation system.

As stated I've fitted Jim C's sump breather, as part of this install I cut the original breather hose shorter coming out of the back of the timing case & blocked it with a bolt & a hose clamp. Any problems with doing this?

The bike has the MK2 spam can air filter for the twin MK1 amals. The breather from the oil tank is routed to a pipe at the back of the air filter housing plate, its at the bottom of the plate. Anybody see any issues with this?

I know Jim C. is cautious on blocking the oil line to the head and rightly so but I'm going to give it a try. It will give a definite area in the engine where the issue lies! Unfortunantly getting a bit late for a roaring Norton in my neighbourhood so I'll wait till tomorrow.

Once I do this test I'll make my mind up on what to do next, ride it like I stole it or pull the barrels :)
 
Could be the mufflers are loaded up with oil now so you'd be unable to tell if it gets fixed. You really need to ride it for some distance. Revving it in the garage is not so good for the bike either. Do you have a big floor fan?
 
batrider said:
Could be the mufflers are loaded up with oil now so you'd be unable to tell if it gets fixed. You really need to ride it for some distance. Revving it in the garage is not so good for the bike either. Do you have a big floor fan?
Click to expand...

Thanks for your reply.

Aware of issues with running a bike on the bench, I only run for 5mins & I have a fan at the front of the bike. I tend to do this 2-3 times just to do an initial heat cycle on the engine for re-torqueing the CH bolts.

I checked the spark plug earlier & I found oil on the plug so new oil is getting into the combustion chamber.
 
i would look in the ports to see if they are wet with oil but i doubt that it is a problem with the guides, when you said it takes a few minutes to start smoking. IMHO and what i have seen in doing this for many years a guide will smoke on startup as the oil has run down while parked and an intake guide will pull more oil at idle or over run when the vacuum is high. my vote is look at head gasket seal at push rod area than oil rings.
 
Status
Not open for further replies.
Back
Top