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Discussion Starter · #1 ·
Hi there! Since I´m a pre unit freak I don´t know the unit motors...

My friends 650 unit triumph chopper has gone mad! Suddenly he´s got problems with a pressurized oil tank, when he revved it at the freeway he blew of the oil tank cap(push in rubber style). By the way the oil tank is a aftermarket custom hexagonal one. What can the couse be? Worn piston rings creating increased pressure in the crankcase? I remeber reading something a long time ago about some pressure valve cousing the same problem?

We are about making a compression test today, if the piston rings are badly worn or broken we should get a higher compression value if we fill some oil in the barrels trough the spark plug holes, right?


Any ideas of waht couses the high pressure in the oil tank!???

Many thanks// Henrik
 

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Hi Henrik,
The bore would not make the slight bit of differece to the return flow from the pump, that would blow out the crank breather!
There Are two reasons First check for a blocked vent in the tank,
Second he's drained the oil in the tank filled it up and not drained the sump so to much oil in the system,pump returns fills the tank to much oil pop goes the cap and one leg covered in oil.

Cheers Dick.
 

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Discussion Starter · #4 · (Edited)
dirtybirdpunk said:
is the tank vented?
Thanks for your fast replys!! :)
The tank cap is vented.

thebaron said:
The bore would not make the slight bit of differece to the return flow from the pump, that would blow out the crank breather!
- My friend has got an oil line running from the bottom of the crank case, back to the oil tank. I thought if the piston rings was badly worn that would couse an increased crank case pressure, if that pressure is blown back into the oil tank so....??

Thanks again! // Henrik
 

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Discussion Starter · #5 · (Edited)
Compression test results!:
Cylinder 1:
Dry: 150psi (1050kPa)

A little oil in the jars: 210psi (1450kPa)

Cylinder 2:
Dry: 175psi (1200kPa)

A little oil in the jars: 200psi (1400kPa)

To me the results prove that that rings are letting pressure trough, but I dont know how tight sealing they are when new, anybody??

Thanks again! // Henrik
 

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I wouldn't run hose from bottom of crankcase to tank.That is a vent for up and down movement (pressure) of pistons in crankcase.I think it should be to atmospere (open to air).If your worried about dirty air being sucked into engine,on up stroke,put a small filter on the end.Hope this helps.
 

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fuzzagogo said:
Thanks for your fast replys!! :)
The tank cap is vented.

- My friend has got an oil line running from the bottom of the crank case, back to the oil tank. // Henrik
Henrik -

first, if that 'line' you mention is from a crankcase vent, it should not go into the tank, stock they vent to the atmosphere, a long hose running to the rear fender's rear edge ..

there are two oil lines between the tank and the pump, which both connect right below the gearcase cover ..

and keep in mind what Baron said about the crankcase possibly having "wet-sumped" - filled with oil - then more oil added to tank would exceed your capacity ..

see, the oil pump is in reality two separate pumps, and the return side is bigger, so it can always draw/pump More oil out of the case than the feed side is pumping in ..

to verify youre not wet-sumped, there's a hex plug at an angle under the centre of the case - a sparkplug socket fits it .. has a screen that slips over the oil pickup on it .. pull that plug, there should be minimal oil there ..

also, I've never seen a "push-in rubber" plug that was vented .. the tank itself should have a vent up top that nneds to be open, not connected to the engine's vent ..

it allows for venting the pressure increase from your oil having warmed up ..

Good luck ..

.

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fuzzagogo said:
Thanks for your fast replys!! :)
The tank cap is vented.

- My friend has got an oil line running from the bottom of the crank case, back to the oil tank. I thought if the piston rings was badly worn that would couse an increased crank case pressure, if that pressure is blown back into the oil tank so....??

Thanks again! // Henrik
Hi Henrik ,
I ment To mention has he a pipe back from the breather to the tank, if so has he another vent from the tank if not this will
pressurize

 

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Discussion Starter · #9 ·
The strange thing about the issue is that my friend has owned the bike for like 5 years, newer made any changes to it, the former owner built it in the early -90:s. I guess he have pulled of like 10 000kilometers on it. And suddenly one day...... He used to have a non vented cap until he blew it on the freeway, I mean the set-up have worked for many years.... strange.... Late night philosophy...:rolleyes:

Thanks everybody for your quick replys!! You rule the world!!
 
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