Leak Down Test (Don't Laugh!!)

click

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OK Lads, need collective Norton grey matter applied to this one!

Bike: 1975 Norton MK3 with 920 conversion (Norvil)

Head rebuilt by THE best, you know who he is :) This has only a few miles on the head, so brand new.

Approx 12K miles on the bore.


Problem, oilly plug RHS, smoke after 3-4 minutes after warming up on bench. Had bike out, pulls like a train, great acceleration, ticks over like a clock but lots of smoke from RHS while blipping the throttle.

Did a compression test, 180 both left & right.

Just did a leakdown test, both left & right about the same (see pics).
I have cheap Chinese gauges & a crappy compressor (that's the don't laugh moment!!) but I'm using this setup for comparison rather than 'accurate' data. There is a bit of 'gurgling' from the breather tube in the oil tank (I have Jim C.'s lower crankcase breather fitted) from both the LHS & RHS, same sound from both.

So, my thinking is this:

Compression is fine & leak down is fine on both left & right hand side. My limited knowledge is telling me that this indicates that the valves, seals, guides & top rings on the pistons are all OK.

It points to an oil ring issue on the RHS, would anybody agree or disagree with this diagnosis???

OK, IF it's the oil ring on the RHS has anybody used any 'snake oil' concoctions in an attempt to 'loosen' the oil ring if its stuck from carbon build up?

Could running the bike on a good spin, 100 miles, have any chance of 'loosening' up the oil ring so it gains functionality again?

My theory obviously presumes the oil ring is stuck as opposed to broken, When I had the head off both of the bores looked the same i.e. no gouge's on the RHS bore etc.

I'm obviously trying to avoid taking the entire top end apart, head, barrels etc. just checking if I have ANY other options?

Is my thinking sound???


LEFT HAND SIDE
LHS.jpg

RIGHT HAND SIDE
RHS.jpg
 
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I'd bet on valve seals!

A leak down test (or a compression test) does not test valve seals - they test valve/seat sealing. If the valves are seating/sealing properly in the combustion chamber but the valve stem seals are bad, everything will test OK but the cyls will smoke as oil is pulled in past the seals when the intake valves are open on the intake stroke. Smoke when blipping the throttle is a classic symptom of bad valve stem sealing - either bad seals or excessive guide/stem clearance.
 

click

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I'd bet on valve seals!

A leak down test (or a compression test) does not test valve seals - they test valve/seat sealing. If the valves are seating/sealing properly in the combustion chamber but the valve stem seals are bad, everything will test OK but the cyls will smoke as oil is pulled in past the seals when the intake valves are open on the intake stroke. Smoke when blipping the throttle is a classic symptom of bad valve stem sealing - either bad seals or excessive guide/stem clearance.
Appreciate the reply. Jim C. did the head & uses kibblewhite valve seals, all new guides & valves (Black diamond etc.), it got the 'full monty' treatment!!. I had the head on the bike, had the smoking issue & sent the head back to Jim just to be 100% sure there was no issues with the head, he retested the head, so I'm 101% sure it's not the head.
 
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My 76 had the exact same issue. The valve seal had popped off and was riding up and down on the valve stem , it was that simple.
 

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Also forgot to say, after I refitted the head, I left the rocker covers off & observed the oil level in the top end while the bike was running, normal levels & good drainage from the head.
 

click

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My 76 had the exact same issue. The valve seal had popped off and was riding up and down on the valve stem , it was that simple.
OK, I'll look at the valve seals just to be sure but I did have a quick look at them & they seem fine.

I know I can do the test disconnecting the oil line to the head & running the bike to see if the smoke disappears, confirming the issue is in the head (seals etc) but I'm nervious doing this as I don't want to cause any damage to the top end!!!
 

rvich

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Sounds to me like you check the valve seals on the way to tearing it down! Or just go ride it. If you don't look behind you the blue smoke trail isn't as irritating. ;)
 

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Sounds to me like you check the valve seals on the way to tearing it down! Or just go ride it. If you don't look behind you the blue smoke trail isn't as irritating. ;)
I like your thinking ;)
 
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How long does the engine run before the smoking begins ? I would time that with a watch. Then do the blockage to the head oil feed line test. If no change in smoking then likely pistons or gasket ? I understand the apprehension of doing this test... but remember it won't be for long and much earlier motors used remote oil squirt manual hand pumps to lubricate the valve stems and rockers.
 

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How long does the engine run before the smoking begins ? I would time that with a watch. Then do the blockage to the head oil feed line test. If no change in smoking then likely pistons or gasket ? I understand the apprehension of doing this test... but remember it won't be for long and much earlier motors used remote oil squirt manual hand pumps to lubricate the valve stems and rockers.
On the bench approx. 3 mins before I see smoke. I'll do another startup tomorrow & time when I see smoke then man-up & do the oil line removal test, more anon.
 
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One path of test pressure into crankcase &or oil sucked into chamber is via the tain't area of gasket / pushrod tunnels or oil drain hole. It takes about a min at harmful slow warm up idle to reach head, then some time to fill rockers to drain 'full' flow past gasket. Bad rings smoke most on starts and worse on throttle. Valve components smokes most once hot and worse on let offs.
 

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One path of test pressure into crankcase &or oil sucked into chamber is via the tain't area of gasket / pushrod tunnels or oil drain hole. It takes about a min at harmful slow warm up idle to reach head, then some time to fill rockers to drain 'full' flow past gasket. Bad rings smoke most on starts and worse on throttle. Valve components smokes most once hot and worse on let offs.
Thanks hotbot appreciate the reply.

I did check the flow of oil from the head through the drain holes at startup & no significant amount of oil was building up in the head/rocker spaces. I had the engine running for 5 minutes on the bench ( I don't normally 'warm up' my bikes before use but for this type of testing I feel I have no choice!

I understand bad rings smoke worst at startup BUT if the two compression rings are OK & the oil ring is not sealing, would it take a few minutes before the oil built up on the barrels and then into the head?

I'll do the test removing the oil feed to the head tomorrow to see if this changes the smoking situation!
 

comnoz

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Click,
The type of valve seals I use do not pop off. But I recently had one of the heads I did leak around a guide due to porosity in the valve guide bore.
If you don't see any cylinder wall damage once the head is off you might want to send the head to me and I will do a dye test to see if there is any leakage into the port. Jim
 

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Click,
The type of valve seals I use do not pop off. But I recently had one of the heads I did leak around a guide due to porosity in the valve guide bore.
If you don't see any cylinder wall damage once the head is off you might want to send the head to me and I will do a dye test to see if there is any leakage into the port. Jim
Jim, thanks for the reply. I, in fact, already sent the head back to you :) (I can only imagine the amount of heads you work on in a year!!) When I originally got the head back from you I installed it & did some road testing, re-torqueing etc. etc. I had smoke coming from the RHS so decided to pull the head & send it back to you just to be sure the head was not the problem (the bike had not been smoking like this prior to the head rebuild). You did the dye test and it was a OK, hence my comment that I'm 101% sure the head is OK.

This is why I'm leaning more towards an oil ring being stuck as all my compression & leak down tests seem fine?

What do you think about removing the oil line to the head just to see if the smoke stops, to point to or exclude the head?

Thinking of running the bike on the bench until I see smoke (time how long this takes as per Torontonian suggestion) then block the oil line & run it for the same amount of time & see if the smoke stops.
 
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1975 Norton MK3 with 920 conversion (Norvil)
OK Lads, need collective Norton grey matter applied to this one!

Bike: 1975 Norton MK3 with 920 conversion (Norvil)

Head rebuilt by THE best, you know who he is :) This has only a few miles on the head, so brand new.

Approx 12K miles on the bore.
If I recall correctly, the 1975 Mk3 came with an RH4 head which is notorious for cracking along the axis of the port in the roof when installing replacement or oversize guides. That cracking is a good source for oil from the intake spring pocket. Been there, done that. Might be worth a look.

Head gasket and mating surface conditions are good places to check. Also see if you can confirm the rocker spindles are installed correctly.

See if there's any hint of oil on the intake side RH port and look for a crack. You don't need to dismantle the head for this though a dye penetration test would be the ultimate test.

I've never heard of a stuck oil ring though most of my experience is with three piece oil control rings. What type of oil control ring came with the 920 conversion, one piece or three piece (rails and expander)? I've seen and read about a few botched installations of the three piece oil control ring as well as experienced the consequence of one of a set of Omega pistons that was not drilled for oil relief but you would have seen symptoms before pulling the head. I doubt an oil control ring rail would break; maybe the expander broke or became cross wise.

Based on what you gave us, if there's no crack in the port, it really sounds like a head gasket issue where oil is getting in to the RH combustion chamber. If I recall correctly, the 920 conversion takes the bore from 77mm to 81mm which leaves very little margin between the pushrod tunnels and cylinder bores. What style of head gasket are you using - solid copper or flame ring?
 
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1975 Norton MK3 with 920 conversion (Norvil)


If I recall correctly, the 1975 Mk3 came with an RH4 head which is notorious for cracking along the axis of the port in the roof when installing replacement or oversize guides. That cracking is a good source for oil from the intake spring pocket. Been there, done that. Might be worth a look.

Head gasket and mating surface conditions are good places to check.

So there was a conversion to 920 with about 12,000 miles then you decided to freshen up the head. Can you elaborate on what lead you (or compelled you) to pull the head after the 920 conversion? Was there smoke before you pulled the head and had it worked on or a lust for more speed and power?

Just trying to get the chronology and whole picture.

I've never heard of a stuck oil ring though most of my experience is with three piece oil control rings. What type of oil control ring came with the 920 conversion, one piece or three piece(rails and expander)? I've seen and read about a few botched installations of the three piece oil control ring as well as experienced the consequence of one of a set of Omega pistons that was not drilled for oil relief but you would have seen symptoms before pulling the head. I doubt an oil control ring rail would break; maybe the expander broke or became cross wise.

It's fun to speculate!
OK!, I'll do my best to keep this short!

I purchased this bike with the 920 conversion already done. It was built by a chap in the UK who had retired & as his hobby was building Norton Commando's (I think he built about 8 bikes). He & his mate shipped two 850 MK2 Commando's over to the USA which he had rebuilt and did a 12,000 mile trip before shipping them back.

I was lucky enough to get this MK3, which he built for his brother in law but was never used. It was then sold to a mate who used it a bit but let the oil run low & seized a piston. At the time it was more cost effective to do a 920 conversion, so this was done & I purchased the bike when it had about 500 miles on the 920 conversion. It had a total of 2400 miles on it.

I put about 9K miles on it but over a span of 10 years (I know shameful!!!)

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.

Eventually I sorted a head with Jim & this brings us up to date.
 

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Unless it managed to overlap somehow after installation and riding for 12,000 miles, "click" would most likely have seen smoke from day one.
Was just about to say the same!

Because the bike has had VERY light use & ends up sitting for large periods of time unused, this is why I'm leaning towards the oil control ring being gunked up & is maybe stuck (unlikely I know!!)
 
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