Burning oil and leak down test on the Shed
 

Ok, so the 'shed' as it is referred to by the GMers (GSXR750 K1 28,000m apparently) likes to use oil at a staggering rate. Let's say after a hard 100 mile round trip, it goes from F to halfway down the window. I also get some smoke sometimes at high RPM. I'm not fussed. I'm enjoying having this bike as a learning tool for maintenance, so I'm prepared to learn about replacing rings if necessary. Bring it on!!

I bought a universal compression tester a few months back, suitable for cars and bikes. Of course, it didn't fit the gixxer, so that was a waste of cash. Now I've just read up about leak down tests and basically finding out where the air is escaping, so I reckon I should give that a go.

My basic understanding is:
For each cylinder:
- Get the piston to TDC.
- Lock engine (in gear, rear brake on)
- Attach tester and fire in 100psi of lovely air
- I should be able to read a leakage %age from the gauge, with upto 10% generally being acceptable
- I should be able to listen to exhaust, valves etc. to determine where the air is leaking through and then book a week of my life and several hundreds of my lovely pounds to fixing it

My questions are:

- Does anyone recommend any particular gauges or tools, or have a better cheaper method? I don't really fancy going on ebay and buying posh testing gear I may never use again, or doesn't fit the bike.

- How do I determine if a piston is a TDC? Will I be able to see it through the spark plug hole? I assume I get it there by leaving the bike in gear and turning the rear wheel?

- I'm not 100% clued up on valve adjustments, so not sure how they impact the testing. If air comes out the exhaust, is this definitely rings, or could it be exhaust valves? Should I be doing valve adjustments before I perform this test?

- Critically, I've heard I can just replace the rings which is relatively cheap (plus a few gaskets), but I'm guessing when I open it all up I'll need to be able to determine if I have more pressing problems. i.e. cylinder reboring and new pistons. Don't have the experience to make the call on that one. Anything obvious to look for, or can rings generally be replaced by themselves unless there're serious issues?

Sorry for all the questions. Figured I might as well ask them all now so I'm mot clued up. :) Cheers for any advice.

Re: Burning oil and leak down test on the Shed
 

Surely if air comes out the exhaust it's nothing to do with the ring? Happy to be wrong. Air from the exhaust would indicate a poor valve seal for whatever reason. Worn rings would allow air to escape into the crankcase?

Re: Burning oil and leak down test on the Shed
 

Bear in mind the 10% is completely arbitrary based on the flow restriction of the tool. Often with cheap tools it's good to check against a known good motor to get a baseline.

I can't remember exactly but do your spark plugs start with a C like the SV? If so then you need a 10mm thread fitting.

Re: Burning oil and leak down test on the Shed
 

Unless the air goes from the crankcase through another worn ring and out an open exhaust valve in another cyl.. Though I havent worked on a big 4t engine yet, only my smaller bikes back in the day. So my advice on rings wont be that good, but I changed them my 125s and once needed an oversize piston.

Re: Burning oil and leak down test on the Shed
 

You need to make sure there is #some# valve clearance otherwise they won't seal.

You've got an oil problem, this means oil is either getting into the cylinder, intake tract or exhaust tract.


By looking to see when the smoke comes out you can get an idea. Ride it and find out what conditions of throttle, revs, overrun/acceleration etc make it smoke. Then pull it in bits slightly and see if there is oil in the headers/exhaust tracts, can you see it on the plugs, can you see it on the back of the intake valves... etc. Which cylinders it is affecting.

Re: Burning oil and leak down test on the Shed
 

It really doesn't smoke noticeably to me. On a number of occasions I've stonked past someone at over 10k rpm only to ask them later if they saw any smoke and got a 'no' as the answer. I can't see it in my mirrors. The only time I've ever seen smoke out on the ride was once when we were at lights and I gave it a rev and covered everyone behind me in a cloud of lovely smoke. We may have been going fast before (hence high RPMs) ... I think we were, but it was months ago.

When I start it up it starts fine and idles fine, and smokes a bit, but it's hard to tell in this weather if that's due to the temperature or chuffing out old oil. It's white by the looks of things, so assuming cold weather water vapour. Within 30 seconds it's warm and not smoking and idle is closed. So really despite it going through oil like a mofo, there aren't any obvious visible symptoms apart from a few mentions by people of smoke at high RPM.

Also there's no leaking around the engine or into the fairing belly.

The only other thing I can remember is some oil residue on the valves which the airbox sits on when I was changing the plugs over when I first got it, and some oil around the air box area, but about the same time I discovered a pipe wasn't connected. It looked like it ran from the crankcase up to the airbox, so assuming it was responsible for the oily residue.

As you can tell I know a bit but not enough about all this stuff to make clear judgements, nor are there any massively obvious symptoms which suggest where the oil is going.

It sounds like from what you guys are saying that really I should learn more about valve clearances and all that shananigans first. I've never adjusted a valve so that's probably the place to start then. Sound fair?

Cheers for your help.

Re: Burning oil and leak down test on the Shed
 

That pipe was I'm assuming was the crankcase breather. Is the airbox excessively oily? I have heard of air being forced past the worn piston rings during the compression stroke thus pressuring the crankcase. Then oil and air out of the crankcase breather into the airbox or indeed where the pipe is hanging. This also puts fuel into your oil which isnt good for the engine. Just speculating though.

Re: Burning oil and leak down test on the Shed
 

Petrol doesn't hang about long in the oil in that sort of dose, it's bloody hot in there tha nos.

But yes it can make it oily if that happens.

You should probably at least learn about timing a motor up and stuff before contemplating pulling the head off.
Not a bad engine to learn on though a bit harder than an SV.

If it smokes badly when giving some beans after overrun then that can say rings or intake valve seals.


Start with basics, what do the plugs look like?

Re: Burning oil and leak down test on the Shed
 

When I took the old ones out when I got the bike (had it about 6 months) the plugs looked ok. I have no idea when the previous owner last changed them. Could've been weeks, could've been years (very little history). Did I mention this bike was a bargain? :) It looked like standard wear though, no obvious fouling or anything. When I bought the 'universal' compression tester that didn't fit I took the new plugs out and they looked good too. Can't remember if I took all of them out though. It was several months ago. I'll have another look and see how they're doing.

Apart from that oily residue around the airbox where that breather pipe wasn't connected, I can't think of any other obvious symptoms. It starts and runs totally fine. I might say the oil was darker than I'd expect it to be on the last change. I reckon I'd done about 2k miles tops since the last change and it was dark and well used, though no signs of metal filings or anything. Nothing on the magnetic sump plug either. I'd probably put a whole litre of new oil in over that time span to compensate for leakage.

Last oil change was only 200 miles or so ago, so new oil and filter hasn't made any difference (semi synthetic castol).

It has a slight 'burble' at idle. Like up down, up down, up down very fast, but I've noticed other gixxers making this noise, so think it's a characteristic of the IL4. But perhaps a symptom of something else?

Can't think of anything else to tell you. I fixed a leaking alternator cover a few weeks ago. New gasket has sorted that. Can't see it being the problem. I spend quite a lot of time arsing around with the fairing off, including a very thorough ACF50ing before xmas, so would expect to have noticed any additional leaks anywhere.

Re: Burning oil and leak down test on the Shed
 

Oil always looks black, sometimes on really new motors it still looks a bit gold.

No oil on plugs suggests either it's only doing it when there's enough heat to burn all the crap off, or it's coming out of the exhaust valve stem seals. Pull the pipes off and have a look if there's a lot of crap in them