Engine bore wear out

In my formative years (before engine management systems). I first visually checked to see if there was detectable sideways movement of the piston in the bore; if you could see movement - do the rebore thing. Secondly (to confirm stage one) the bore was filled with low viscosity oil. If the level was maintained for more than an hour, the piston/ bore was O.K., if not (and repalcement rings was not the answer) the rebore thing was the only option.

If you're wondering, it's probably time.

compression test works too

buy a manual [or find one online]

if the plugs are black & it uses oil, probably time

sometimes thicker oil will buy a few miles

The cheapest way: look at the spark plugs: oily or black plugs mean oil consumption.

More accurate: compressiont test.

If the motor is already disassembled: look at the cylinder and if you can see an edge close to the top, it's time to re-bore it

if made in U S A bore and keep ---------if not made in U S A toss in trash and buy made in U S A

To answer your question

there is a inside diameter gauge shaped in a t that slides in the bore and provides accurate measurements .

If not available a feeler gauge can be inserted next to the piston to determine wear remember to check at different levels of travel .

If within tolerance rings are easy and a quick hone will prevent glazing.

On an older machine avoid chrome rings use old style soft rings to ensure break in.

oversize rings are available but stock is easy and foolproof

The gauge you are referring to is called a "dial bore gauge". Just for your info.

There is a simpler and more accessible t gauge aka. {slap gauge} that is spring loaded and holds the measurement and is removed and measured .

The dial gauge is preferable of course but my assumption is the gentleman is working in remedial conditions and might not have gizmos available .

If it has a dial, otherwise it is referred to as a snap gauge! Once the measurement is taken, it is then read using an outside micrometer. The dial bore gauge will produce more consistent readings and is easer to use.

IT IS NOT, NOT, NOT A SNAP GUAGE!!!!!!!!!!!!!! It is a Telescoping guage.

A snap guage is a very high precision device for quickly measuring OUTSIDE diameters. (It's really a comparitor.)

Bad spelling, please proof read or use spell checker before sending!!!

A leak down test is a very good method of testing leak past the rings before openning the cylinder up. I do compression tests and leak down tests both to make the decision to open in up.

But you bore dial gauge is what to check the cylinder with for out of roundness, bore diameter and taper. Check against spec and either rehone if in tollerance and check again or overbore or resleave.

If you dont have any of the fancy gear listed above (compression tester, leak down tester, snap gauges, etc. ) a simple first observation you can make without removing the cylinder head is to run the engine and look for a smokey exhaust, usually blueish black in color (although thats somewhat subtle). This is usually means oil is burning which indicates piston ring/cylinder wear. Of course I'm assuming your bike is a 4 stroke engine found in most bikes and not a 2 stroke found in dirt bikes. You can also check your oil and see how black it gets over time. If it seems to get black rather quickly, again, burning oil.

Todays four stroke engines use plasma sprayed chrome molly rings. The coating is a propriety Molly based metal composite. Remember, when was the last time you heard someone needing a ring job. This is why. Any burnt oil will normally be caused by the oil passing the valve seals in the head. If you are burning crank case oil a simple compression test will easily determine either a worn bore(s) or a cracked ring. The rule of thumb is head first cylinder second.

Lubricating oils burn blue, quite clearly.

Fuels, both petrol and diesel, if the fuel to air mix is too rich burn black.

A worn out engine with a badly adjusted fuel to air mix will give both blue and black.

Above is assuming a 4 stroke engine of course, but if the motorbike has a 2 stroke engine, you will have to think again!!!

Mr Idiotalways did not specify the engine type....

Hi, can you give us a little more info? There are 3 basic things that will give you a power drop. 1) a bad fuel air mix. 2) poor ignition and 3) poor compression. You could be dealing with any of the 3.

The first 2 are much easier to fix than the 3rd. Is the engine a 2 stroke or 4 stroke?

Once you eliminate all of the ignition and fuel/air mix problems the compression checks listed are reasonably appropriate. Leak down compression test is the first and easiest next is measuring the bore diameter for size, roundness and taper and comparing it to the size of the piston both of which you want to check for wear and compare to the factory specs. The piston is measured with a micrometer and will likely not be round particularly if it is a 2 stroke and is not supposed to be. Also the piston will probably be smaller at the top than it will be at the bottom also the way it's supposed to be. The cylinder can be measured with "snap" or "T" gages and a micrometer which is very accurate when done by a practiced hand or by a bore gage which is quite expensive but is quick.

Also, where are you? There are people all around the world that love to play with this stuff that have the equipment and would be glad to help. If you're in the Seattle, WA USA area I would be happy to show you how to measure your parts and find out if they are in/out of spec. There are others around the world that would happily do so as well.

Scooter

First off these guys are obviously engineers and not motorcycle mechanics. The first question is 2 or 4 stroke? If the motorcycle is a 2 stroke than you can go ahead and re-ring it. When you do this you will need to hone the cylinder and replace the head and base gaskets. By the way compression in a 2 stroke is good over 110psi. Any less and maintenance is necessary.

If it is a 4 stroke and loss of power is the problem than do a valve adjust and ride it again. This is the most common cause of lost power. The next logical step would be compression and leak down tests.

Simplicity.

You left out engine designers! The best fix for a two stroke engine is to buy a cheater piston and ring kit. This will take in account the the slight out of tolerance of the bore. Now two strokes cylinders are (late model) made from an aluminum alloy. The bore is treated using a hole host of coatings. The most common is Nickel-Sill which is applied directly onto the bore. These coatings will not allow you to bore out the cylinder or at times hone it either. So for a two stroke late model motorcycle, mic. the bore and piston. If they are in spec. (buy a manual) then just change the rings and scuff the cylinder. New gaskets and proper torque and torque sequence and go. GAS!!!!!!!!!! High octane pump 92 will work fine. If your oil is fully synthetic run the mix 50/1 Castor based etc. 32/1 P.S. if you cylinder or piston is out of round check your crank...its bent.

A compression check would be my first test. If comsiderable compression is lost your performance will suffer.

If you are loosing compresion. hte next test is to pressurize the chamber. If the air escapes into the intke or out the exhaust, you kow it is your valves. If not the air is passing by the rings into the crank case, and you need new rings, or possibly a rebore.

How many miles on it? How long since you gave it a tune up?

It may simple need a tune up instead of a rebuild.

If it has had a tune up- meaning new plugs, plug wires, timing set, and carb set. Is the spark as viewed in the spark plug blue? If not look into the ignition system. Next, is it burning oil? The simplest check is that you have needed to add oil to the reserve-assuming 4 stroke. Next, and if it's a two stroke pull a spark plug and look at it. It is covered in burnt oil? If yes take your flashlight and look into the spark plug hole and view the top of the piston. There should be a pattern to the burnt oil on top of the piston. You may need to move the piston either up or down in the bore to get a good view.

If there is a non burnt spot in the middle then your valve guides are leaking oil and your engine needs a head job. If there is a non burnt area around the edge of the piston then the rings are leaking and you probably need a ring job.

Get a compression and leak down test before you decide to rebuild an engine.

Three weeks ago, I got done working on a Harley that had 159,000+ miles on it. It still had good compression (155psi in each cylinder) but the cam was worn to the point that there was very little lift left.

A worn cam will also reduce power. Like any other moving metal part it can wear out. Your lifters or push rods may also be worn out if you have a high mileage engine.

My question was, how do I get the feel with normal riding conditions other than the most of the metrological solutions found here.

Mr. Idiotalways

That's hard to quantify, you would have to have made a timed run before the motor wore out, so you have something to compare to. as others have said simple tune up items can make a huge difference in proformance. Depending on the size & # of cylinders of the motor, the difference will show more in a smaller motors. Other factors are wheel bearings, tires, chains, brakes will all effect the power output.

ok, lets try a different approach, we still don't know if its a 2 or 4 stroke but with the info given if your trying to find out just by riding you really only have 4 clues. Sound, smell, sight and feel(acceleration and heat). Sound doesn't tell you much because with time the exhaust system degrades and the sound gets louder and the higher pitch exhaust notes come out that you didn't have before. Now smell is a different thing.

All of this applies only to a 4 stroke. With smell and sight you can look for oil burning blue smoke when excelerating if your rings are worn, blue smoke when launching if your valve guides are worn. You can also smell the burnt oil first thing when your starting the engine from both causes and get a cloud around yourself that stinks. If your getting black smoke and you smell gas its rich, lean is harder to tell it runs hard and hot and smells hot. Spark plugs help with this (sight), they should be brown, white and they are lean, black they are rich.

I can't help you with a 2 stroke other than the measurement info I gave you earlier. I don't run rings in any of my 2 stroke engines.

Scooter

"I can't help you with a 2 stroke other than the measurement info I gave you earlier. I don't run rings in any of my 2 stroke engines."

What does that mean?

All the rest of the advice is good sound basic troubleshooting.

alwaysanidiot probably has something simple like a clogged air filter, worn out plugs......

I make very high performance 2 stroke engines as a hobby. I don't use rings. My engines use very closely fitted, very carefully selected materials and rings can't be used at the performance levels I'm getting. The engines are small at 2.5cc but I'm getting almost 2bhp @ 40-42k rpm's with them on alky/oil. I did experiment with a 125cc engine back in the early 80's and got 42bhp @14k rpm's but I was using a Yamaha crankshaft and I couldn't keep it together and dropped the project.

Scooter

Very cool

any links?

what kind of dyno goes 42k?

What do you power w/them

inertial dyno's are what you have to use and you have to make your own. The data is actually taken by how fast you accelerate a flywheel.

Scooter

The 1st video looks like the hammer throw, I like the part where it take more than 1 person to counteract the power.

The original questioner refers to how to determine the problem by "feel". They already "feel" that there is a wear problem. This is probably because the rider has put many miles on the bike (2 or 4 stroke) and senses that wear may be an issue either by having to add oil at least twice as often as usual (4 stroke, no observed leakage problem) or an increase in exhaust smoke (both 2 and 4 stroke). Of course the rider can remove the spark plug to look for oiling and IF they have a compression guage, get some indication of condition, but at that point nothing can be done to correct the problem.

The next step is to remove the head, right? Well, if you've got the head in your hands, SEND IT OUT!! And if you're already at that point, the cylinders come off with not too much more effort usually. SEND THEM OUT!! Change out the piston and rings. Put it all back together. GET BACK OUT AND RIDE That's the "feel" your looking for. And you won't have to worry if the engine is worn for a long time.

Smoke coming out, accompanied by an intolerable oil consumption, would be a good indicator.

...as would a fall-off of performance since new/purchase, particularly at full throttle.

My son was a former motocross rider,a 2 stroke losing power is very evident.Some reasons are bad or dirty reed valve,clogged or restricted exhaust,and in non competitive type,a clogged spark arrestor.Wrong or old fuel(Methanol mixes are not good in a 2 stroke)old fuel will accumulate moisture.Wrong oil type.Make sure the oil you use is BIA rated(low ash). An oil-rich mixture is not the same as a fuel-rich mixture,just the opposite.Best power is developed using less oil,but make sure the oil is rated at 50:1 at least, for a normal 20:1 ratio.We used 40:1 ratio in races with 50:1 oil.No problems even in extreme conditions.

Check the carb for cleanliness,and experiment with the needle valve position for best results.Moving the needle valve clip down will give richer mix.

Clean or replace the spark plug.To properly clean,use a propane torch to burn off the carbon,then use a wire wheel or brush to remove the ash.Some modern fuel anti knock compounds will not come off unless you burn them off first

A 2 stroke only has one ring because there is no crankcase oil below the piston,only fuel mix.The ends of the ring are notched and overlap to provide a seal.

2 cycle engines are simple to rebuild,we used to do a rebuild after every race:basically rings,reed valve clean,spark plug replacement.

There are companies that can bore the hardened cylinders using a diamond tip bore bar,but it is usually cheaper to replace the cylinder.

Hope this helps.