Leak Down Test (Don't Laugh!!)

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WZ507 said:
I wonder if the 3-4 minute wait for smoke is somewhat of a red herring. Perhaps the elapsed time to start of smoking is simply related to combustion chamber temperature and nothing else. It is possible that upon initial start-up the combustion chamber is too cold to combust liquid oil in the chamber, hence no smoke. However, with further warm-up the combustion chamber comes to temp and the oil present begins combusting and smoking, rather than just being moved through the combustion chamber in uncombusted liquid form.

As far as thrashing the engine, I thought you indicated it had 12K mi on it, so any chance of altering the ring performance seems likely 12k mi in the past.

When you removed the head previously for inspection was carbon thick on top of the piston or was it mostly washed off the top of the piston. I ask because if the piston top was mostly/partly clean it suggests the oil is coming from below. If the piston top has a thick layer of carbon building up I’d suspect the leakage is from somewhere above (head or head gasket).

Interesting problem you/re working on and excellent job of communicating the background of the project and the observations as you progress.
Click to expand...

Appreciate the reply.

Interesting theory re: bore heating up, this could explain the time delay before seeing smoke

I think the 'redneck tuneup' approach is an attempt to loosen up a stuck oil ring not to bed it in as that ship has sailed!! Very much an outside long shot!

Find below a pic of the RH piston after the initial fitting of the head, it matches your theory perfectly. There's actually oil pooling in the valve recesses on the top of the piston. This was after doing 5-6 miles approx. with some blasts up to 90mph.
 

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If you look at the picture, the rim of the piston has a coating of residue around it's edge everywhere except where the oil leak from the pushrod tunnel is washing away the residue. A head gasket leak at the pushrod tunnel is my guess. Why your compression tests and leakdown test doesn't show a gasket leak, I don't know...

The first time I rebuilt my commando I couldn't get the copper gasket to seal. I tried twice with 2 different gaskets. I was young and doing the work myself with no internet to consult, so I didn't really know that I had to anneal the gasket to soften it. Maybe the copper gasket would have worked had I annealed it properly, but instead I bought a flame ring gasket which has sealed perfectly every time I've pulled the head off.
 
It did show as slight sounds form crank case in leak down with tests eliminating other paths. Commandos commonly have more than one thing at once both causing the same thing.
 
o0norton0o said:
If you look at the picture, the rim of the piston has a coating of residue around it's edge everywhere except where the oil leak from the pushrod tunnel is washing away the residue. A head gasket leak at the pushrod tunnel is my guess. Why your compression tests and leakdown test doesn't show a gasket leak, I don't know....
Click to expand...

:) Yep, re the pic, I totally agree re the head gasket leak and ALSO am totally mystified how a compression check and a leakdown test didn't easily identify it. Either test should have! Believing that both together would fail to identify it is right up there with believing the Patriots were going to come from 25 points down and beat the Falcons in Superbowl 51!

Oh...right...:(
 
Hi Lads,

Slight confusion again due to my lack of clarity!! There's two parts to this story:

PART1
The picture above is from the first time I installed the head I got from Jim C. I ran the bike for 5-6 miles & had the smokey issue on the RH cylinder. After consulting with Jim I removed the head, took some pics and sent them to him.

I did a compression test which were fine BUT I didn't have a leak down tester at the time.

ALSO I had NOT annealed the copper head gasket, rookie mistake, as I always anneal copper gaskets!! I did spray the gasket with copper coat.

I then sent the head back to Jim C. just to be 100% sure there were no issues with the head.

As hotbot stated you can sometimes have more than one issue contributing to the fault. In this case I think I shot myself in the foot not annealing the CH gasket BUT I feel the oil ring on the RH bore is still dodgy.

PART2
When I got the head back from Jim C. with a clean bill of health I checked the barrel deck for flatness.
I also got the reduced shank CH bolts.
I got a new copper cylinder head gasket AND annealed it!!
I used thin copper wire & Pliobond around the pushrod tunnels & the oil return hole (I know some say this is not a good idea, some say use silver paint or copper coat, some say don't use anything!)
After I heat cycled the engine twice on the bench I did a compression test AND leak down test & posted the results on this thread.

So, THE IMPORTANT BIT, the picture you are viewing is from PART1, I have NOT removed the head yet from PART2. This is were I am now. My plan is to bring the bike for a good long spin & see if anything changes, if it stays the same then the head, at least, is coming off & I'll have more pictures to show.

Does anybody know if a flame ring is available for a 920? To my knowledge the only option is a copper gasket.
 
worntorn said:
The piston looks to be up rather high, maybe I'm seeing things.
What is the CR?
Click to expand...

The conversion was already done when I purchased the bike. The 920 conversion is from Norvil, piston & liner kit.
I just checked their site & they have the CR listed as 9:1
 
Everything points to the oil control ring, but could the presence of oil from the pushrod tubes have fooled the leakdown tester? I know it can make a compression test look a lot better than it really is.
 
Does anybody know if a flame ring is available for a 920? To my knowledge the only option is a copper gasket.[/QUOTE]

Try contacting Cometic:
http://www.cometic.com/
You won’t see it on their webpage but they respond to their e-mails and phone calls. They are very helpful. Give yourself some lead time because if they don’t stock them they have to make them up.
Only pitfall is the minimum (I believe) thickness is .043”
Good luck,
Pete
 
Danno said:
Everything points to the oil control ring, but could the presence of oil from the pushrod tubes have fooled the leakdown tester? I know it can make a compression test look a lot better than it really is.
Click to expand...

I could be wrong about this but my understanding is that its possible that the two top compression rings could be OK but the oil control ring is not & oil is not 'scraped' from the cylinder walls and makes its way into the combustion chamber.
In this scenario the compression & leak down test would look good due to the two top rings sealing OK. I'm sure the oil plays a part in the equation!!
 
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Deets55 said:
Does anybody know if a flame ring is available for a 920? To my knowledge the only option is a copper gasket.
Click to expand...

Try contacting Cometic:
http://www.cometic.com/
You won’t see it on their webpage but they respond to their e-mails and phone calls. They are very helpful. Give yourself some lead time because if they don’t stock them they have to make them up.
Only pitfall is the minimum (I believe) thickness is .043”
Good luck,
Pete[/QUOTE]

Hi Pete,

Thanks very much for the contact, I'll ask if they have anything for a 920 Norton! I'll report back on any info. I get

Excuse my ignorance, why is .043" a pitfall, is it very thin hence raising the CR?
 
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This is all starting to make my hair hurt! ;)

I'll just go back to my first reaction; tear it apart (head/barrels) and start over!
 
Have you overfilled the oil tank? If I overfill mine it spits oil out of the breather, as your breather feeds into the air intake maybe that is how oil is getting into the engine. I also have an S which I have blanked off the breather that comes out at the front of the central oil tank and re routed it to a spigot I soldered into the oil tank filler neck.
 
MexicoMike said:
This is all starting to make my hair hurt! ;)

I'll just go back to my first reaction; tear it apart (head/barrels) and start over!
Click to expand...

You and me both, re: hair!!!. I think the problem with these long threads is that we don't tend to read all the info & respond based on what we think rather than what has been said, I've done it myself, really appreciate all the info. so far.
Gilesy said:
Have you overfilled the oil tank? If I overfill mine it spits oil out of the breather, as your breather feeds into the air intake maybe that is how oil is getting into the engine. I also have an S which I have blanked off the breather that comes out at the front of the central oil tank and re routed it to a spigot I soldered into the oil tank filler neck.
Click to expand...

Hi, my oil level is set purposely to low as I didn't want overfilling to be in the equation. Before initial startup I drained all the oil & put a set quantity in.
 
click said:
The conversion was already done when I purchased the bike. The 920 conversion is from Norvil, piston & liner kit.
I just checked their site & they have the CR listed as 9:1
Click to expand...

I think it might be quite a bit higher than that. It looks like the pistons protrude above the cylinders by a fair bit.
Unless the combustion chambers have been changed a lot, this would correlate to a very high Cr. Are the pistons flat top or domed?
This is only relevant to your problem in that it is a lot of compression to hold in with a copper gasket( if I'm correct about the CR)
The compression test at 180 correlates to somewhere between 10 and 11 to one Cr.

Glen
 
click said:
You and me both, re: hair!!!. I think the problem with these long threads is that we don't tend to read all the info & respond based on what we think rather than what has been said, I've done it myself, really appreciate all the info. so far.


Hi, my oil level is set purposely to low as I didn't want overfilling to be in the equation. Before initial startup I drained all the oil & put a set quantity in.
Click to expand...

Do you also drain the sump?
 
Click,
Re: gasket thickness
I believe most standard copper and the old flame rings were .030”. New AN flame rings are .040”. Some people go even thinner than .030” on their copper gaskets. Depending what you are currently using a .043” will probably lower your CR slightly. Looking at Glen’s post about CR it will probably not make much of difference.
FWIW. There are a lot more knowledge people on this forum than me on things Norton, but if I were you and the head is off I would pull the barrels.
It’s not that much more work, you get to see the entire bore and rings. Take some measurements and put new rings in. One more thing, I had a blocked vent tube and had a similar problem, the way I found out was while the engine was running I opened the oil filler cap and heard a rush of air come out.
Pete
 
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