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Use ATF in the primary. It works well and since it is red in color you can easily tell if the leak is from the engine or primary.


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I tried the flashlight and mirror trick but couldn't really see the breather outlet very well. I'll have to take the chain off and try again. In any case, I turned in the throttle stops by 1 full turn, so probably about 2500 rpm, but no oil was leaking out while I watched (about 5 minutes). But after I shut it off, maybe a thimble full of oil dripped off the bottom of the lower chain guard (part of the case). It seems as though it is really a higher rpm leak, with very little leaking at lower rpm, but seems to be accumulating somewhere.

So if the timed breather happens to be in the open position when the motor is shut off, is there some residual oil that accumulates in the camshaft trough that can leak out? This motor is a '65.
Originally Posted by koan58
Somehow bodge in a bottle, or tube and bottle,, using string or wire, so to catch what comes out of the breather tube. Then you will know.

Good idea but hard to do. I'll look as another motor I have to see if there is any way to snake a copper or plastic tube up into the breather hole to confirm the source.

Just saw your post Htown, so I'll try that as well.

Tom

Last edited by koncretekid; 07/03/20 10:53 pm.

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Hi Tom,
I am working on an A10 that is doing similar strange things
I found a few issues that while different to the A65 other checks I have to do will be the same

I need to remove the oil tank and devise a way to flush out the return stand pipe, Today I was told of a case where a random piece of gasket goo or other object would get pushed up the return pipe at high revs and partially block the outlet, stop engine and it would fall back down and hide till the next time

Another check to complete is to check the oil pump gasket then the mounting bolts plus the screws that hold the pump together for tightness to make sure there are no leaks

If there is a sump plate with magnetic plug fitted to your A65 either remove the magnet or place the plate with the magnet furthest away from the pickup pipe. I have first hand experience of the magnet causing the ball in the pickup to stick shut

John

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Not possible to bodge a tube into the breather without taking the motor apart. It is just above the gearbox high gear bearing in the back of the main case. Without the chainguard you should be able to see it.
You have an early engine, so you have a seal between the primary and motor? Which way is the seal lip facing? It sounds as though you might be pressurizing the primary through the seal and it has no where to go but out the generator wire hole, sprocket door seal or the chain drip feed. Do you have an inspection cap with the tiny weep hole it it?

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My Thunderbolt has always leaked oil from the primary. Like I posted earlier I use ATF since the engine and primary oil are separate on BSA's and the red color is a dead give away. One place it leaked was the primary adjuster bolt. Fixed that with some thread sealant. But it always dribbled out the back of the case. Mostly I ignored it and checked the fluid level regularly. This spring it got so bad that it was starting to get on the tire. I pulled the primary apart, replaced the seal in the sprocket door and installed a new gasket. I also plugged the chain oiler hole from the case side with silicon and sealed the alternator grommet with some. Dang think still dribbles slightly after a ride. I give up


1978 Bonneville T140E
1974 Trident
1970 BSA Thunderbolt
1971 Norton Commando
1972 Norton Commando
1973 Norton Commando
1974 Norton Commando
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Quote
. Dang think still dribbles slightly after a ride. I give up

the ill-conceived chain oiler hole is also a breather . weres the primary vent hole now ?
when you seal up one hole ... sometimes it just moves the leak .

Some people report that running a vented clutch adjuster plug
allows enough venting without leaking ,

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Get yourself3 different coloured oils
Put ATF in the primary and different coloured oils in both the gearbox & the engine
Take the bike out for a short ride then prk it over a sheet of something white and adsorbent
Look at the colour of the oil\

Sounds silly I know but it is the fastest way to track down a phantom leak
Royal Purple used to make a nice bright purple gear oil which is great for this.

If the leak is mostly rd then the oil is coming from the primary.
If that is the case, drain the primary .
If the oil is polluted with the engine oil ( get a green one if you can ) then you know the primary seal behind the sprocket is leaking

If the oil is green then you have a bottom end problem.
Could be as simple as a leak from the oil manifold

And of course if it is purple then the oil seal on the sleeve gear is the prime suspect, followed by the splines followed by the gearchange lever

Remember that the oil will almost never drip from exactly where it is leaking from because that would make life way too easy.

A long length of hose on the oil tank breather is also a good idea just in cse you have excessive foaming and overflow from the oil tank.


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I found primary covers earlier than 70 always prone to leaking because of common opening for oil level and oil dumping with screws holding a cover to the engine. In both cases ( both bottom screws ) oil gets by a gasket and on the threads of screws with only possible way to stop a leak by some seals or gaskets under those screws, which never works 100% in my experience. Have such a cover now, and still no idea how to deal with this problem.

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Adam,
My cover is apparently later model, with separate level and drain screws. But, I noticed how chewed up the screw seats were, so I spot faced them all to 7/16". Not having a 7/16" end mill, I sacrificed an extra 7/16" bit and ground it to work as an end mill. I also glass sanded the inside of the cover but if you look closely, you'll see how little "meat" there is around the surfaces on the inside of the cover as well as the screw seats on the outside. It's no wonder it's not easy to get a perfect seal. I had already sealed the gasket to the cases with RTV Silicone, so just grease on the outside of the gasket. I also gooped up the screws before I screwed them in .
[Linked Image from i.postimg.cc] Spot facing of screw seats.
[Linked Image from i.postimg.cc]
Inside surface of primary cover.

Tom


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Oil can also leak out of the alternator wire tube.

A good move on the cover screws is to use the small copper washers used on the Triumph
unit 500 rocker box allen screws, they are 1/4 washers but have a very small o/d.

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I find fibre washers are good at sealing leaks from the cover screws, the size I use is 1/4 id, 3/8 od and 1/16 thick. These fit nicely under the socket cap heads and dont foul the cover.


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Hi Tom, you are lucky to have this cover. Gasket surface on mine is reduced to perhaps 2.5 mm near the oil dumping bolt, oil channel is bypassing gasket on oil level bolt altogether. I will have to use some alu, copper or fibre washers under those screws.

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To determine more precisely where the oil is leaking from, I devised a "bodge" consisting of a shortened 1/4" barb fitting drilled out as much as possible, screwed into a 90 degree 1/8" NPT pipe fitting with a 3/8" shortened barb fitting with a 3/8" oil line which I epoxied into the breather outlet. I had to remove the rear wheel, chain, and chain guard to be able to snake this into the hole and hold it in place over night for the epoxy to harden.
[Linked Image from i.postimg.cc]
I also discovered that the screw I used to block off the chain oiler was not tight so was able to tighten that as well as a few other things like adding a 7th plate to my clutch (machined off the lining of the first plate and added another plain and friction plate) and replaced a bad rotor. Before the rain came (yay!) I was able to get in another 22 miles of spirited riding and brought the bike back in and placed a container under the newly installed breather hose along with some paper towels. This is the result after about 5 minutes:[Linked Image from i.postimg.cc] The plastic container catches the oil from the breather, and the paper towels show the remainder of leaks.The next photo shows leakage which shows up on the fins of the cylinder head indicating other leakage, which looks to be from the rocker cover.[Linked Image from i.postimg.cc]

Another compression test indicated I was able to achieve about 160 psi after 10 good kicks. I then got out that leakdown tester I said was junk to see if I could make it work. I had to back up one O ring connection with a spark plug washer to stop it from leaking, then discovered that the quick connector just needed to be tightened, and replaced the right hand gauge which failed with one from an old compression tester. Unfortunately, because it reads to 300 psi it was hard to read actual leakage, but the right cylinder actually registered zero leakage. I could not hear any air leakage at 100 psi, anywhere. But the left cylinder did leak, apparently about 10% and that was at the breather as an audible leakage.

So I'm left wondering if the rings on the left cylinder haven't seated yet, or if there is head gasket leakage? Is 54 miles just too little to expect the rings to seat? Is there anyway to determine if it is the rings or the head gasket? The oil I'm using is 20/50W Castrol 4 stroke MC oil type SG/JASO M2, which is the only MC 20/50w oil I can find.

Tom

Last edited by koncretekid; 07/08/20 9:15 pm.

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Check it again at 300 and 500 miles. It’s most likely rings haven’t fully seated yet, in 54 miles the bike hasn’t had much time to run in. Providing you anealled your head gasket I doubt it would blow after that mileage. You stand more chance of having leakage at/around the spark plug or from the valve seat.


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Sorry if I’ve said this before, but John Healy’s dry assembly and Pete Russell’s (rest his soul) big second ring gap have seen bloody great ring sealing on my bike.

Compression test showing 170 psi, with a 7.25:1 compression ratio ain’t bad.


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Apart from the breather hole leak, there seem to be leaks from several other areas including the chaincase screws and rocker cover. These leaks may be caused by overpressurization of the crankcases, possibly because of ring blowby and/or problems with the breather disc.

In the short term maybe you could add fibre washers to the chaincase screws and rocker cover studs to stop leaks. In the longer term, it might be worthwhile adding an extra one-way breather/reed valve to the rocker cover to help maintain negative crankcase pressure and stop leaks.


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You did well to fit that breather catch pipe, thats a tricky access,
the front drip is most likely the primary chain adjuster, the rocker box leak may be oil passing down the stud, plumbers tape will fix that.
Have you retorqued the head after a couple of heat cycles, ?The centre bolt on my head usually nips up a tad more.


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Originally Posted by Allan G
Check it again at 300 and 500 miles. It’s most likely rings haven’t fully seated yet, in 54 miles the bike hasn’t had much time to run in. Providing you anealled your head gasket I doubt it would blow after that mileage. You stand more chance of having leakage at/around the spark plug or from the valve seat.
I annealed the head gasket and sprayed it with 2 coats of Permtex copper coat.
Originally Posted by triton thrasher
Sorry if I’ve said this before, but John Healy’s dry assembly and Pete Russell’s (rest his soul) big second ring gap have seen bloody great ring sealing on my bike.

Compression test showing 170 psi, with a 7.25:1 compression ratio ain’t bad.

Allan, I haven't read Mr. Healy's dry assembly, but I lightly coated the cylinder walls and then wiped the oil off with a clean rag leaving just a whiff of oil. Then oiled the skirt only and installed the pistons with rings. My notes are out in the shop, but the ring gaps were all .014" or more.

Originally Posted by gunner
Apart from the breather hole leak, there seem to be leaks from several other areas including the chaincase screws and rocker cover. These leaks may be caused by overpressurization of the crankcases, possibly because of ring blowby and/or problems with the breather disc.

In the short term maybe you could add fibre washers to the chaincase screws and rocker cover studs to stop leaks. In the longer term, it might be worthwhile adding an extra one-way breather/reed valve to the rocker cover to help maintain negative crankcase pressure and stop leaks.

Gunner, I had previously spot faced all the outside screw holes on the primary cover screw seats. I used annealed copper washers on the rocker dome nuts as well as a bit of RTV sealant, but maybe fiber washers would work better. The cover itself was glass sanded; the head surface was only planed with a 12 lathe file. I agree with the possible over pressurization causing some of the leakage; just need the rings to seal unless it's the head gasket. A one-way valve may help, but there shouldn't be that much leakage/pressurization if everything else is tight.

Originally Posted by gavin eisler
You did well to fit that breather catch pipe, thats a tricky access,
the front drip is most likely the primary chain adjuster, the rocker box leak may be oil passing down the stud, plumbers tape will fix that.
Have you retorqued the head after a couple of heat cycles, ?The centre bolt on my head usually nips up a tad more.

Gavin, I had already siliconed the primary chain adjuster on the inside, but maybe still a drip. I used ATF in the primary to see if it leaked red as was suggested. No sign of red oil, and although the primary oil will get dark, I wouldn't think it would in just 22 miles. As far as rocker box studs, I hadn't thought of sealing those and when I remove it to re-torque the head bolts, I'll try that. I've only gone thru 3 heat cycles and 54 miles, so I'll probably just put some more miles on it before I do that to see if the rings will seat better.

Thanks for the suggestions.

Tom


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I can see you've done a good job prepping the chaincase so maybe the leaks aren't from the screw holes at all but could be drips from the cylinder head.

Interesting post from a few years ago where someone had a similar problem, see This link


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It looks like the primary chain case is pretty well sealed. It also looks like in the second picture that there is a vertical streak of oil up the primary cover about three quarters of the way back. So that suggests oil is coming from higher up. The oil tank may be venting some oil. Check around where the breather line from the oil tank is venting. When are you checking oil level. Always do it after a ride when oil is hot as it expands. I generally run mine about half way between the marks. Seems like if you run it at the completely full mark some goes out the tank breather. The leak on the fins looks like it is coming from the rocker box cover. It's only on the top fins so unlikely head gasket.
Your compression of 160 psi sounds like the rings are seating to me. I'm still a bit puzzled why the oil comes out the breather.
If it's not using much oil and is running well, I believe I would try to put some miles on it. I've used the same Castrol oil to break in several engines successfully.


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Went out today to put some miles on it. 5 miles out, it seized up. I disassembled it this afternoon expecting top end damage of some kind, but not. The left connecting rod is seized to the crank.

Interestingly, the head gasket looks close to blowing on the right side, but that was the side that showed no sign of leakage.
[Linked Image from i.postimg.cc]
The problem is done here:[Linked Image from i.postimg.cc]

Waiting for a pickup, I snapped a nice photo of the girl.[Linked Image from i.postimg.cc]

I'm headed out for a few days, so the rest of the tear down will have to wait.

Tom

Last edited by koncretekid; 07/09/20 11:51 pm.

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Amazing (and fortunate) that you could seize a rod to the crank without snapping the rod and/or putting it through the piston or the case!

Left big end seizure is typically due to oil starvation and nothing to do with the upper engine.

Inspect the crankcase very carefully. When I trashed a lower (due to oil starvation; I won't go into that here), I didn't notice the two little partial punch-outs at 4:00 and 8:00 until someone else (who knew what to look for) pointed them out. But my conrod was loose, not seized.

Sorry to hear you're "back to the drawing board".


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Plus 1, that’ll be oil starvation. I had this, it cost me a rod (probably didn’t have to but I thought it best) set of shells, and being very lucky was able to polish the journal. There was no damage to the journal itself (the seizure happened at very low speed, I knew something wasn’t quite right so started to limp back to camp)

The shells surface melted and spread itself up both sides of the rod effectively wedging the rod against the cheeks of the crank. Fine wet and dry and metal polish cleaned it up fine. I then had the crank nitrided (I don’t think it was long before that hill billy biker did something similar to his race bike and the journal was sound after the bike had been nitrided)

Might be a good time to check that your oil pipes are connected the correct way around.


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If the journal has the bearing lining stuck to it then hydrochloride acid will remove the Aluminium/tin and not touch the steel crank. Not sure if it work on bronze material. Tip I picked up from Briggs engines with a Aluminium rod which seizes on the crank.

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Please tell us you don't intend to re use that rod


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