well looks like im going to be needing, at least, rings in my 90. i was wondering how far can the cylinders be bored, without having to do anything to the cases. im getting a little smoke out of the pipes and also i can see some blow-by coming out of the vent hose, not a lot but some. i might get lucky and just be able to re-ring it, but figured if it needs to be bored how much can i go and would it be worth it to max it out.

 

Just take it to the first oversize that cleans it up and get HD pistons and Hastings rings that size, with the jugs honed to match, of course, and all done with the torque plates by someone that knows how to do Evos. Trying to pick up a few CC's by going bigger on stock everything else is chasing a lot of nothing. In my opinion.

 

I agree. When the factory stuff finally gives out, most often you'll need to go oversize. It starts with .005, .010, .020, .030 and trying for more zip with simply doing an overbore is a waste of time and money. Hasting rings for certain, regardless of the brand of piston you choose and I won't offer an opinion about them except to say, don't pay big bucks for a big name.

I've put on base gaskets WITHOUT taking the pistons out of the jugs (used same rings) and I've also honed mine with 22,000 on the cylinders and pistons (no torque plates) put new Hasting rings on the same cheap pistons. Had great sucess on both counts. No oil use in 12,000 miles since the new rings and 155 compression to this day. But again, when the factory stuff is worn out, you need to bore and hone it properly with torque plates.

 

hotrod351 How many miles on the bike ?

 

not sure of the mileage, i bought it from the original owner, its a 90, and it was his only transportation. said it was rebuilt 35,000 before i bought it. i know it was rebuilt because i had to helicoil a head bolt and therefore had to pull the front cylinder. tried to put the piston from the bottom, backwards and it wouldnt go, at least it didnt just slide in. so i figured it was tight. it has harley pistons. i figure it was at least re-ringed and maybe bored, i should of checked it out closer when i had it apart. i guess the only way to find out is to take it apart. local shop wants $150.00 to bore them, seems like a lot to me. i see decent piston/ring kits on ebay for around $200.00. i know a lot of these bikes can just be re-ringed and that will stop the smoking, but for the long run, bored, pistons and rings is a one shot thing.

 

Assuming it's already been bored and the pistons aren't scored or worn, hone it well with a ball hone (dingleberry hone) put in new rings and run it is what I'd do. Most HD shops get 250.00 + for boring. Rings are about 25.00, hone is 35.00 - 50.00, gaskets about 50.00.

 

Any of the prices listed are not unreasonable for machining of bore & hone esp. for a DIY cost for the hones, torque plates, measuring tools, etc. Note: the EVO has "oval" pistons (round out after heating up) making them virtually impossible to measure accurately at home. Have you done a compression & leakdown test? You haven't described any performance or starting issues so I would do these tests and check out "other causes" for smoking (such as carb settings, clogged oil return passages, etc.) before doing a rebore.

 

starts as it as always started, perfect, runs perfect, doesnt miss a beat. only smokes, a little, when i mess with it for 20 or 30 minutes sitting still. plugs are perfect, light grey and clean, no build up. compression is 130 but the engine isnt really turning over that fast. it does have a cam, which i dont know, but it has vthunder adjustable pushrods and i dont think they were put in for the hell of it. who knows it might stay like this for a long time or get worse next week. in that case ill take it apart and see what it needs, rings, pistons and bore. i think if i look around enough i might find a like new set of pistons and cylinders some one has taken off to go with a big bore kit.

 

UH, you should NEVER "mess with it" for more than 2 - 3 minutes sitting still. The compression is a little down from a fairly fresh top end but certainly not in need of rebuild going on what you've said. It's getting overheated and they'll ALL smoke when that is going on

 

If you do decide to re-ring or bore it and re-ring it(piston clearance will decide which), hasting makes a good ring, but Yotal seal makes a great ring. We get less than 2% leakdown with them. Go on their web site and check them out. Hope this helps.