Engine Piston

[RASTA]

HI, i am new in this forum, i have a 82 gl 1100, but recently it starts to smoke, i took it to my mechanic and he is asking me to get the four pistons set in .25, i already try to find them but i haven't get too much lucky that's why i am here asking for help, so if anyone of you know a web page where y con order it i will appreciate too much, thanks

[Rednaxs60]

Before I would be taking the engine apart, I would confirm the piston issue. Need to do a compression test to confirm there is an issue. To localize the issue you need to do a leak down test to determine if it is the piston rings, intake or exhaust valves. It's quite expensive to have a shop do a piston change and you need the rings as well. A complete gasket set is in order as well.

You mention the bike just started smoking. What colour is the smoke? Blackish would indicate oil, white would indicate steam/water.

Your mechanic has requested pistons .25 over size, or does he mean 0.025" oversize with the requisite piston rings. You will also have to confirm that there is no machining of the cylinders to accommodate oversize pistons.

These are questions I would want to ask.

Good luck.

Cheers

[RBGERSON]

1st are you sure about this mechanic??? second cheaper to find a "new" motor than rebuild one. Third very hard to find all the parts you need to rebuild, like main bearings.. fourth do all teh tests above. More info on the bike has it sat a long time..if so rings may loosen up with a little use. What are the compression numbers and do it right with throttle totally open. Does adding a little oil to cylinders bring numbers up?? = rings issue if not = valve issues. Lots of things to do before going to a rebuild or engine swap.

[DaveO430]

You are not going to find any oversize pistons.

[DaveO430]

Your mechanic has requested pistons .25 over size, or does he mean 0.025" oversize with the requisite piston rings. You will also have to confirm that there is no machining of the cylinders to accommodate oversize pistons.

I'm sure he meant .25mm, not .025". The cylinders would have to be machined in either case. Not that it matters, no such thing as oversize pistons anyway.

[RASTA]

First of all, thanks to all for the interest in my case and your info, first the color of the smoke its between white and kind of blue, it smells like oil, before a take my bike to the mechanic (which is a 72 years old man with all the experience in this old bikes and a friend since 2015 ) y took of the spark plugs and two of them went wet which something that looks like oil, and two of them went dry and with traces of a good combustion, the problem is that when i start my bike it smokes a lot but with the time it stops and runs perfectly, it only smokes when its cold, thats why my mechanic says that de oil ring is damaged and we need to change it, but i haven't have time to go to the workshop and check it personally, so if its quite imposible to get the pistons .25 and the ring set, what can i do?, the option of get a used engine its not my best because i just already get one and this is the engine that I am trying to fix, i really haven't too much luck with this bike but I just have too much time, love and money invested in this bike and I don't want to give up. thanks and i hope you can give me some more advises.

[Rednaxs60]

You're probably using the side stand a lot and these older flat four engines will tend to smoke on start up then clear up. You can try parking the bike on the centre stand and compare start up smoke. This condition is also indicative of valve stem seals needing to be replaced if the smoking did not clear up.

You mention the plugs are wet and dry. Are the plugs wet on one side only, and the other side dry? A culprit for this condition are the carbs, and how the carbs are set up.

Have you checked the compression yet? If it is low, 125 or less, you may need to lap the valves. In conjunction with the compression test, a leak down test will indicate where the main issue is helps as well and mentioned before.

Lots to do before tearing the engine apart.

Hope this helps.

[RASTA]

You're probably using the side stand a lot and these older flat four engines will tend to smoke on start up then clear up. You can try parking the bike on the centre stand and compare start up smoke. This condition is also indicative of valve stem seals needing to be replaced if the smoking did not clear up.

You mention the plugs are wet and dry. Are the plugs wet on one side only, and the other side dry? A culprit for this condition are the carbs, and how the carbs are set up.

Have you checked the compression yet? If it is low, 125 or less, you may need to lap the valves. In conjunction with the compression test, a leak down test will indicate where the main issue is helps as well and mentioned before.

Lots to do before tearing the engine apart.

Hope this helps.

At the beginning i only used the side stand but someone told me the same as you, so i decided to use only de center stand wile the bike is park on the garage, then i bought the carb synchronizer to tune up the carbs, and finally we try bay changeing the valve seals, but it doesn't stop smokeing, i certainly don't remember if we check the compression, do you know between which numbers it supposed to be in the right numbers?, and, do you know if i change only de rings without machining of the cylinders could be right or its really necessary to machine the cylinders?, thanks

[RBGERSON]

170 perfect
160-169 excellent
150-159 -very good
140-149-good
lower than 140 manual says time for rebuild but they will run OK down to 120's even 100's

If low add oil to each cylinder and retest if they come up = ring issues. If not valve issues

testing done with throttle wide open stop run off.

[RASTA]

170 perfect
160-169 excellent
150-159 -very good
140-149-good
lower than 140 manual says time for rebuild but they will run OK down to 120's even 100's

If low add oil to each cylinder and retest if they come up = ring issues. If not valve issues

testing done with throttle wide open stop run off.

thank you so much, i will try this and be sure y will let you know.

[DWade1990]

Be careful making final calls based off compression numbers. I've had wildly different readings on the same motor when using different compression testers. They're not all of the same quality or accuracy. The thing to look for is grouping. It's very rare for all 4 cylinders to fail at the same time. Look for consistency between all 4. Say you have three at around 130, and one at 90, you clearly have a problem, but if you have all four with a similar reading, even if it's not what the manual calls for, you likely need to look elsewhere for your problem.