Compression and leakdown testing

[yorkie_chris]

Dizzyblonde has a bike thats burning oil, I've seen various leakdown testers, but they're all a fortune.

Anyone built one? What did you use?

[Blue_SV650S]

Dizzyblonde has a bike thats burning oil, I've seen various leakdown testers, but they're all a fortune.

Anyone built one? What did you use?

leakdown is the way to go, but a little trick if you don't want to get one is to do a compression test, then put a teaspoon of oil down each bore and do it again. If the compression goes up, its the rings that have gone, not a leaking valve :)

Its not as foolproof as a proper leakdown, but its better than nowt!! 8)

[ejohnh]

leakdown is the way to go, but a little trick if you don't want to get one is to do a compression test, then put a teaspoon of oil down each bore and do it again. If the compression goes up, its the rings that have gone, not a leaking valve :)

Its not as foolproof as a proper leakdown, but its better than nowt!! 8)


Good idea!!

[toonyank]

Dizzyblonde has a bike thats burning oil, I've seen various leakdown testers, but they're all a fortune.

Anyone built one? What did you use?

How much oil is being consumed? I ask because mine goes through 500ml in about 5000 miles. Mine doesn't smoke blue and I think that amount over that milage is probably normal. After all if it's lubricating the cylinder wallls it consumes oil. Also it's not like a car with oil and compression rings there are only compression rings.

If it's alot of oil then that's different.

[yorkie_chris]

Also it's not like a car with oil rings there are just compression rings.

Are you sure of that one?

It's not normal consumption, its stinking of burnt oil and throwing a smokescreen when cold starting!

[toonyank]

Well that's why I said if there's alot of oil that's different. Blue smoke and everything.

I thinks bikes just have compression rings. At least back in the day that's the case and never had my twin apart yet. I don't think there are oil rings. Could be wrong though. I'll get the manual ;)

[yorkie_chris]

Not blue, white on startup. So thinking valve seals, maybe exhaust. Not entirely sure.

Here's one for the oily fingernailed brigade...

If it's piston rings, would the smoke come from excess blowby forcing oil out the breathers into the airbox, or from oil getting up past the rings? Or even both...

[toonyank]

Are you sure of that one?

Wrong my mistake :( I was thinking of my 2 stroke days where there's no oil sump and just compression rings. SV's have 2 compression and 1 oil ring doh!

[ejohnh]

So what exactly is a leakdown tester? How does it work?

[yorkie_chris]

some pressure > gauge 1 > orifice > gauge2 >cylinder head

Like that.

If theres no leakage, then there will be no flow through the orifice, the gauges will show same pressure, the more flows through the orifice the greater the pressure drop over it.
About 10% is considered normal difference as some leak is inevitable.

All AFAIK, only seen one built and used on car engines, (a mental 2l pinto to be exact :D)

[toonyank]

Not blue, white on startup. So thinking valve seals, maybe exhaust. Not entirely sure.

Here's one for the oily fingernailed brigade...

If it's piston rings, would the smoke come from excess blowby forcing oil out the breathers into the airbox, or from oil getting up past the rings? Or even both...

If the smoke is coming from the exhaust then it's burnt oil. Blowby is when a bad ring allows compression to blow into the crank case thus through breathers etc...

[toonyank]

Sounds a good bit o kit!

[ejohnh]

some pressure > gauge 1 > orifice > gauge2 >cylinder head

Like that.

If theres no leakage, then there will be no flow through the orifice, the gauges will show same pressure, the more flows through the orifice the greater the pressure drop over it.
About 10% is considered normal difference as some leak is inevitable.

All AFAIK, only seen one built and used on car engines, (a mental 2l pinto to be exact :D)

I hope that I'm not being overly obtuse but I didn't really understand that. Is it a particular orifice you are referring to? If so ,which? Where would you apply the pressure gauges or gauge - is it a differential pressure gauge?

[yorkie_chris]

My theory is its getting into the airbox, and thus down the carbs being burnt that way.

Soon check it by starting it looking down the airbox if it is that.

Its the same amount of smoke you get from a stored engine when you've squirted oil down the bores, but for 5 minutes or so, so it should be obvious if its coming that way.

[toonyank]

That doesn't sound right. Just trying to understand.

I can't see the oild making its way to the carbs and into the chambers and burned in that way or you would see other tuning issues. Maybe I'm wrong but I can't see that happening. I think we need an expert. It really sounds like oil is being burnt directly through the cylinders from the crank case.

[yorkie_chris]

I hope that I'm not being overly obtuse but I didn't really understand that. Is it a particular orifice you are referring to? If so ,which? Where would you apply the pressure gauges or gauge - is it a differential pressure gauge?

basically you're blowing air into the sparkplug hole, the feed comes from a regulator, set to a pressure A, then through an orifice of some size 1mm or so is normal, then you have a gauge and the fitting for the sparkplug.

So, with no pressure loss in the cylinder, there's no flow through the orifice, so gauges read the same, 0% loss, if there is some flow, then the pressure will drop in the second gauge due to the restriction in flow.

[yorkie_chris]

I can't see the oild making its way to the carbs and into the chambers and burned in that way or you would see other tuning issues. Maybe I'm wrong but I can't see that happening. I think we need an expert. It really sounds like oil is being burnt directly through the cylinders from the crank case.

Got one, was talking to spanner man the other day about it.

Another possibilty is worn valve guides or seals, as theres a whining/rustling noise as well.

[toonyank]

I'm frustrated now or maybe it late for me buth how does anything to do with valves cause oil burning? When oil comes from the crank case behind the piston.

[yorkie_chris]

Valves get oil feed too, if the valve seals go then oil can leak down into either intake tract, where it gets sucked in and burnt, or exhaust where it gets blown out and vaporised / burnt in hot exhaust

[GastonJ]

Thinking about it, if it was blowby, then the crankcase would be pressurised - so it'd be quite obvious anyway. Probably test that by removing the oil filler and sticking your thumb over the hole. Rev the bike and if your thumb feels undue pressure then it would indicate rings. It would also smoke all the time, and use a *lot* of oil.

As for oil in the carbs, how would it get into the air filter box anyway? Bit high for oil to leak so far upwards, unless it was coming past an inlet valve.

Sorry to say I'd be betting on valve guides, valve seals, or if it also runs rough then maybe a bent valve, which would wear the guide oval and allow the oil to leak past. Not having had an sv in bits I don't know how much movement the valves make in their normal operation. Would one be capable of hitting a piston and bending?

[yorkie_chris]

As for oil in the carbs, how would it get into the air filter box anyway? Bit high for oil to leak so far upwards, unless it was coming past an inlet valve.

Breathers are connected to the airbox.

It only smokes when cold, and has an unrelated oil leak, so its hard to measure consumption of oil.

Valves can hit pistons, but usually only when camchain tensioners have gone AWOL and let chain slip, never happened on this bike as dizzyblondes feller bought it brand new, then she bought it so no history of catastrophic top end munchings.

[GastonJ]

Well when stopped and parked up, oil leaking through the valveguides/seals would accumulate in the bore for when you start it up. That'd explain why it smokes more at startup. Too much oil doesn't leak much past valve guides/seals in any case while running.

If it were blowby I think you'd see the oil burning all the time due to the sheer amount of pressure generated - the oil would be going through quite quickly.

[yorkie_chris]

It's not a quick cloud then thats it, like what you get when an engines been stored with oil in the bores, it smokes for a good 2 minutes untill its warm.

Its white smoke with a definite oil smell, more info soon when can fit it in my garage, plugs and airbox will show where its coming from.

[toonyank]

Valves get oil feed too.......

I'll get my hat and coat :smt090 it's been a very long time for me and 4 strokes. Now I feel like a numpty :smt088

It'll be time to do the valve clearances soon so I'm sure it'll all come back :)

I hope you can get this sorted.

[Spanner Man]

Morning all.

As I said on the blower the other day, you're going to have to get the spanners out & have a gawp.:D

Cheers.

[Blue_SV650S]

It's not a quick cloud then thats it, like what you get when an engines been stored with oil in the bores, it smokes for a good 2 minutes untill its warm.

Its white smoke with a definite oil smell, more info soon when can fit it in my garage, plugs and airbox will show where its coming from.

In that case, it is highly likely to be a blown head gasket!!!

The white is the water from the water jacket, the blue is the oil from an oilway ... when it heats up the gasket is obviously being closed enough to make a bit of a seal ...

take the rad cap off and look in to see if the oil is milky ... same with the 'eyeglass' in the engine ...

[dizzyblonde]

no milk in my spy glass

[GastonJ]

no milk in my spy glass

You do realise that there's a joke in there somewhere don't you?
:smt026

Best of luck with the bike.