Stock appearing kt100
- Thread starter Twinenginekart
- Start date
alvin l nunley
Site Supporter
I feel like I'm on probation here on Bob's, so I'm hesitant to say anything about this statement. I would like to have a better understanding of what you mean by, "compressible volume"? And how do you lose it if you cut the barrel instead of the head?
I just don't understand how anybody can argue that the steel liner would not transfer heat as efficiently as the aluminum head. It's so apparent to me that it's incomprehensible that others can't see it.
alvin l nunley
Site Supporter
maybe you don't understand what a private message is.
alvin l nunley
Site Supporter
as I thought, you don't understand at all.
Dan Brown
Member
Al, I am confused. I owned a machine shop and built a lot of engines in the 1990's, mostly small block chevy's for dirt cars, however I have never built a stock appearing or open kt100. I freshened a pair of kt100's yesterday, one was the old style head and cylinder originally blueprinted by C&G in PA ( never heard of them before) and the other is a 787 cylinder/new head built by Profile. After setting the exhaust and intake port height the pistons basically flush with the top of the barrel. If the top of the barrel was cut more to decrease chamber volume and boost compression it appears there would be an interference between the piston and the cylinder head. To eliminate that interference the chamber in the head would then need to be re-cut to provide adequate squish clearance . Wouldn't the removal of that material basically cause a similar loss in heat transfer? Also, does a kt have heat dissipation issues when heavily modified? I have read here that the cranks are kinda the weak point in a kt, but the only thing have seen about them running too hot is when the fuel mixtures are leaned out too much. Not looking to argue, I am honestly interested as I don't see how the barrel could be cut much more without having to do some machining of the head to compensate for it.
Ted Hamilton
Helmet Painter / Racer
IIRC, a KT-100 was originally designed to be closer to a 125cc, so it has "excess" fin area anyhow....and that's also why it runs just as well with the barrel flipped and the transfer ports misaligned as it does when they're "correct". But I could be mistaken about that. Also, the hotter you can run an engine, the more thermal energy you keep, = more power, unless you're getting detonation or pre-ignition, right? So, I'd think that so long as you're not sticking 'em, why not cut the "easier" side? But I'm not a builder.....yet.
alvin l nunley
Site Supporter
if you put a brand-new head on the engine, one that has not been cut, what would your squish band be? If you think about it, you can't cut the barrel and the head both. All I'm saying is; cut the barrel, what ever amount it would take to get the right squish area, and/or cc's, with a stock head. If you knew what the CC's of the head were, before cutting, you could then calculate how much you need to take off the barrel.
All I'm saying is, don't cut the head if you don't need to, get a new cylinder head. It sounds like your cylinder head has already been cut. You might have to recut the combustion chamber in the head. I actually don't have enough information to make any kind of definitive decision. What would happen if you put in a thicker head gasket?
alvin l nunley
Site Supporter
my suggestion, of cutting the barrel instead of the head, is so you can run hotter with no detonation or preignition. The aluminum in the head is going to dissipate heat much better than the steel of the liner.
I've never heard anybody say that the 100cc KT100 has excessive fin area. I've never heard your assertion that the KT100 started life as a 125 cc engine. It's an interesting idea. Not saying you're wrong, just that I've never heard it
Dan Brown
Member
I actually have a brand new bone stock kt100 here that I just got with a kart I bought. The squish on that engine measure .082. I just pulled the head and it has a horribly machined underside. Someone at the factory started a cut, went about a half inch or so across the face and stopped. That cut is .024 deeper than the rest of the machined surface. It doesn't get into the gasket mating surface so it really doesn't effect anything, but its ugly. I am not sure how much would have to be removed to get down to a 7cc chamber, but with .038 squish I have 11.1 cc on the Profile engine. If I put in a thicker head gasket it would counter act the removal of the material off the barrel, by moving the head up and enlarging the combustion chamber. I am sure it's been done, but I wonder what the results would be if the barrel was bored out real big and then the cylinder wall was done in Nikasil and a coated piston was used. That should dissipate heat nicely and have an extremely low drag which should help it make great power.
Jon Brogden
Member
Al, a stock uncut head has .055 relief, head gasket is .030, he says pistons flush with the the top of the cylinder, surely you don't advocate cutting the cylinder and bringing the piston .050 out of the bore. The Europeans don't build um like that, doesn't that carry some weight for ya? Dan just cut all the relief off the bone stock head and you'll have what you need. The blueprinted heads have had there combustion chamber opened up to make the 11cc tec and have the minimum squish, look closely at the stock head and you'll see the difference. KT's have no heat dissipation problem and it will make little difference whether you cut the head or cylinder. The cylinder top has been cut some already if it had a good B/P to true it up with the bore. If you go big bore (55mm) then leave .015 or so relief in the head so when you enlarge the squish area for the bigger bore, you can go to zero relief again without cutting the original squish area. In other words , if you had zero relief and wanted to widen the area for a bigger bore, the only way to get it wider would be to cut the squish area deeper. You don't want to do that because the Yamaha squish is not a straight angle, it's a radius and on top of that it would reduce the hemi pocket, it's small enough on a stock head. If your gonna run it on gas, back the timing up or detonation will eat it up. Jon
Jon Brogden
Member
Al, have you considered the fact that built the way you advocate your exposing more piston material to combustion heat? The diameter of the head relief is 2.090, a std piston has a 2.035 diameter at the edge of the crown so you have a .027 gap all around the piston just below the crown edge with .050 of piston exposed in the case above. Your worried about dissipating heat when in fact your more than likely increasing piston temperature, that's more heat transfer , but not in a good direction.
jack burroughs
member
Dan, I too have a head cut like that, but doesn't seem to be any different. I have built kt's both ways, cutting jug top and cutting piston, thing is that you can run engine on Alky and not cut jug, leaving it still good for wka stock and have great performance.