Burning oil, compression

First some background.

I've got a 1982 KZ1100 A2 which I don't know much about its history. I got it last winter with 30,000 miles on it from my brother. He only had it one summer and didn't ride it much. He changed the oil but never the filter because the oil filter bolt was buggered to the point where it couldn't be changed. It also leaked oil from the oil pressure sending unit (where the oil cooler lines go, too). So he didn't have any reason to suspect it burned oil (be probably just assumed it leaked out).

First thing I did was check the compression - and got readings at 130,132,130,145 (cold, no valve adjust). At the time I didn't have a manual and it didn't billow smoke and it ran/started pretty good. It had a lot of power so I figured it can't be THAT broken so I assumed all was well and set to overhauling the rest of the bike (forks, battery, shocks, seat, tank, mufflers, carbs, oil leaks, etc).

I also measured and adjusted the valves, fixed the filter bolt and changed the oil. At this point I started riding the bike more and noticed that it burns about a quart of oil every 750 miles. At first I chalked it up to hot weather, but the next 750 miles in cooler weather it burned oil too. So changed to a mobil 1 redcap, thinking a) synthetic = more uniform molecules = less small molecules getting past piston rings, and b) thicker (15w50) weight = less getting past piston rings. It made no difference.

So now I have a shop manual and see that the compression readings should be in the 152-181 range and reading this site I know the valves must be adjusted and the engine warm and WOT when taking readings. So I did that, and get 150,138,138,150 with all the spark plugs out. Ok.. I have two iffy cylinders, but am surprised how different the readings were from the first time, but chalked it up to the valve adjustment.

Then I read about putting oil in the cylinders to see if it is the rings or guides, but this time I did it cold as I read there's about a 10psi difference. Before oil added and engine cold and only one spark plug removed (the cylinder I'm reading) I get 150,150,150,150. Huh? I'm thinking with the other three plugs in it is pulling more air through the airbox (maybe I should remove the air filter? It is fresh). I put oil in the two outside cylinders and it jumps up to about 200psi (I haven't found a good clean easy way to get oil into the middle two without taking the tank off yet).

So here's what I'm thinking:

The piston rings are worn but seem to have enough compression for the engine to run strong. The compression is on the low end, but not really far out of whack. So why am I burning so much oil? (there is no leak).

Post edited by: c_aasland, at: 2006/06/28 10:14

There are two ways for oil to get into the combustion chamber (four if you include a cracked/porous head and a real bad head gasket, both rare), piston rings and valve guides.
Only way to check the valve guides is to remove the cylinder head.

If you are burning a quart of oil every 750 miles, then deposits should show up on your spark plugs, are they?

A quart every 750 miles sounds like a heck of a lot. Are you getting blue smoke from exhaust? How about if you jump on throttle do you then get a momentary puff of blue smoke? I would look at valve seals as main cause. I like the compression test results myself. Could you be blowing it out the crankcase breather?

up to 1 quart per 1000 miles is the normal oil consumption range for an air cooled engine. argue or not that is the fact. for you it is time for a deglaze and some piston rings friend. you will not need rebore or parts if you catch it now. head and base gaskets and a std size ring set for each piston. you'll have the beast all ready for the highway.

steell wrote:If you are burning a quart of oil every 750 miles, then deposits should show up on your spark plugs, are they?[/quote]

Yes, the two middle plugs.

RomSpaceKnight wrote:Are you getting blue smoke from exhaust? How about if you jump on throttle do you then get a momentary puff of blue smoke? I like the compression test results myself. Could you be blowing it out the crankcase breather?[/quote]

No blue smoke from the exhaust, no puffs of blue smoke. My old Camaro had a puff of blue smoke on startup from oil seeping through the the valve guides. I don't see that, so I would guess that indicates it is probably the piston rings?

Where is the crankcase breather on these things?

trippivot wrote: I'm surpised 1 qt/1000 miles is normal. That seems excessive. Perhaps I should have chosen a watercooled bike for touring.

So, let's say that I wanted to deglaze/re-ring the pistons over the winter (my labor is cheap but it takes a while :laugh: ) .. what would the cost in parts be, $100 for rings and $100 for various gaskets, and whatever the deglazing tool costs?

Lordy! Remove that gas tank! Remove all four plugs. OPEN YOUR THROTTLE WHEN YOU CHECK COMPRESSION. Did you have the throttle open all the way? Once you confirm compression making the readings with the throttle open, check in with the results. Also, 1 qt every 750 miles ain't all that bad. You are likely getting a bit of blowby. It gets by the rings some and won't hurt much. Ask Kawasaki corporate what THEY consider excessive oil use and 1 qt every 750 miles is OK... Some of the earlier Vulcans would get 1 qt every 300 miles and Kaw still didn't consider it a problem warranting warranty work. Look for signs of oil residue on your crank breather hose... If it isn't bad, don't consider the oil a problem but the compression MAY BE if you checked it correctly.

BTW: Put ONE teaspoon of oil down a plug hole and check. If you put it down all of them at once, you will blow oil all over the ceiling. Check compression with no plugs in and the throttle open.

Apparently I am incorrect on the oil consumption rate. My old 650 had 75000 klicks and went through a quart of oil in a season (say maybe 3000 miles). I would drain oil at end of year (nov), refil in spring (mar or apr) and have to put in 1/2 quart halfway thru summer and lose another 1/2 before put away. That was riding hard, fast, far and stop and go traffic. Guess I was lucky (!?). My ZX1100 burns no oil over corse of 5000 klick season.

Some bikes are more prone to oil consumption than others. A Vulcan 1500A from the late 80s to mid 90s was prone to piston rocking. This rocking caused the cylinders to oval a tad and it isn't unusual for a VN1500A to use a qt every 500 miles. When the bike was still under warranty, Kaw would claim that the qt per 500 miles was NOT excessive and wouldn't touch it under warranty till it used a qt every 350 miles... oil use is relative. My KZ900s use no oil between changes. While a qt every 750 miles may seem like a lot to someone whose bike uses none, if you work on LOTS of bikes, that really isn't a horrible number or that far out of the normal. Say you ride 5K miles in a season on your KZ. That is 6-7 qts of oil used in a riding season. That comes out to less than $20... when you weight that cost against the cost of a top end rebuild, the oil added isn't all that much.