I just picked up my 87 Banshee, and the previous owner said that he had never replaced the pistons in the 8 or so years he owned the bike. I get the impression that he only rode it for a couple of years out of those 8, and only 4 or 5 times a year each season. He said that it has been stored most of its life.

Either way, I am trying to decide if I should just run it (it still has a ton of power and runs well) or if I should replace the pistons before I even take it out to the dunes.

If I just remove the head, can I tell if it needs a new top end, or do I need to pull the cylinders, take them to get mic'd, etc.?

Thanks,
Dean

 

Dean,
I wouldn't change pistons just for the sake of changing them. If the guy isn't pulling your leg about the amount of time it has been run they should be okay. A quick compression test should tell you what shape the engine is in.

 

Take a compression test.. IF its above 100 and u get the same number in each cyclinder then oyu should be fine.. but if its lower than 100 and u get a different number in each cyclinder get a new piston and rings.. don't ride to it blows cause ur cyclinder walls could be fine and the rings are always the first to go, if you ride it till it blows than you will have to bore it and thats one bore closer to having to sleave it..(wjich is really expensive)

BTW make sure u have an accurate compression tester..

 

Excellent suggestion, I didn't even think of that. I'll get a good tester today and check it this evening.

I agree about not wanting to swap them out just for the sake of it, but don't want to run it till it blows either.

Thanks,
Dean

 

Well, I just did a compression check, and I have right at 98 to 100 psi after I kick it over about 6 or seven times (same on both cylinders).

So, what is the concensus from you gurus, should I take it apart and put new pistons in it and have the cylinders mic'd?

Thanks for any advice you can offer,
Dean

 

Dean,
I wouldn't go so far as to call myself a guru. I do not have any experience specifically with the Banshee engine, I do have much experience with 2 stroke outboard marine engines.

I would personnaly run the hell out of the engine. The compression check indicates the cylinders are healthy. I would consider running a bit richer oil mixture for a tank or two since the bike sounds like it has been stored for a while.

 

I was wondering if the fact that it has been sitting/stored for so long might mean that the cylinders are dry, hence giving a slightly lower compression reading. What mixture would you recommend? I am running Gold Spectro for now.

Interestingly enough, when I pulled the plugs out, they looked to be a bit wet with what appears to be fuel mix (wasn't oil). Also, he was running a B8ES in one cylinder and a B7ES in the other, any idea why? I just figured he threw something in there to fill the hole and that is what he had laying around.

Thanks for all of the help,
Dean

 

vdubn, Did you have your throttle wide open when you were cranking it over testing the compression? If not try it again with the throttle wide open, The engine needs air to breath weather it's running or doing a commpression test.

 

No, I did it with the throttle closed, I'll try that this evening and see if it makes a difference.

My main concern is that 100psi was the break point for doing a new top end, but as long as it is right close to it, it sounds like that should be plenty, right? What is stock compression? I thought I had seen something like 125psi?

Thanks,
Dean

 

make sure when you co your compression check that you hold the throttle wide open, which creates more air to be pulled thru to give a more accurate reading. A pretty much fresh, stock bore banshee cylinder should be right at 120-125 psi per cylinder. Dropping below about 110, I would look into doing the cylinders, especially if you going to be doing any dune riding, which the sand robs alot of power, along with the paddles.