you don't need two kidneys.
Wow... THIS neighborhood went downhill FAST... :smilie_happy:
Joe... just a few points here:
While there is a relationship between fuel energy and output power, one cannot assume that more power automatically equates to 'more heat' in any given context... meaning...
Just because an engine can develop more power, doesn't mean it is harboring more heat than any other engine.
By that: The engine's rate of heat transfer to the cooling system is an independant factor.
An Onan NHCV flat twin of 17hp will be hotter, and disspiate much more energy, and be hotter than a 27hp Kohler Command V... at basically any given load point... First, because the 27hp will never be working hard to match the 17... and second, because the Command V has a better-breathing cylinder head, that has better cooling airflow.
You may have a lot of power on-tap, but you're not generating heat 'just because' it's output is higher. If you want to illustrate it's capacity to generate power and heat, put it on a static-load chassis dyno (not an inertial dyno), and set the load high, put the bike in 3rd gear, open the throttle, and load the dyno to hold engine at 4500rpm for an hour. THEN you'll have an idea of what kind of waste heat it really generates, compared to a road-ride.
Hooch's problem is not temperature... it's SEAL. When you start melting pistons and dropping valves, you're dealing with heat.
You either have an improper gasket seal (which is lack of conformal surfaces, or insufficient gasket design/material, or improper bolt torque), or you have a casting which is cracked or otherwise leaking.
Since it happens most at high load, it is compression pressure, leaking into the cooling jacket.
Remember: Engine block seal is a DYNAMIC thing...it changes based on block temperature. An engine that seals well when cold, sitting on the bench, is not the same as an engine that's spinning at 6400rpm, consuming 6 gallons per hour at 120mph... or at 4100rpm climbing a ten-mile 12% grade.
Head bolts aren't bolts. They're SPRINGS... and their tension changes based on temperature. Bolt threads aren't seal surfaces, and they're not smooth. Tighten two bolts with the same torque wrench, into the same block, and they will NOT present the exact same amount of force. Cylinder heads and block faces aren't flat at any temperature OTHER than the temperature you MILL them at... and even then, they're not flat... and they're not smooth. As a result of these factors, one can NEVER get exact bolt force, and when the engine temperature changes, so does the tension against the gasket.
My gut feeling says you have a simple case of leak around the fire ring of a gasket. Perhaps a re-torque will solve it, but compare the technique you used, with my technique, and consider wether your heads' seals may have reason to leak under extreme circumstances:
When I want a cylinder head to seal REALLY WELL:
- Clean the block holes. I start by digging any crud out of the bottom of the hole with a piece of wire. I prefer NOT to use a tap if at all possible, because it will cut the threads oversize, which I don't want. I'll take an extra head bolt, and wire brush the bejezzus out of it, then put a very SMALL amount of toothpaste on it, run it in, then back out, and then spray the hole out with carb cleaner and air nozzle...
- Clean the bolts or studs. Wire brush, turn them 'till they're beautiful.
- Clean out the head holes. I drop bolts in each one. Don't wanna drill them out, but no crud in them, and the bolt landing face needs to be clean and no big burrs.
- quality head gasket. There's absolutely no cost savings in a poorly-made gasket, ever... and it must fit RIGHT. The bore hole of the gasket must not protrude INTO the combustion chamber... the fire ring defends the gasket against flame, but having it protrude into the exhaust gases causes it to become a 'hot spot' that will cause preignition, and it'll erode under high load regardless, nullifying it's ability to contain compression pressure. (read that three times slowly).
- Flat, smooth mounting surfaces. A precision flat surface is important, and sometimes, hard to determine, but when you've had machine work done, they SHOULD have obtained flatness at shop temperature, during the cutting process.
[we interrupt this program for an aside note: When I'm making a precision part... say... a very close fitting rod in an air-bearing, or a piston in a brake cylinder... I will cut the part to rough shape, leaving it a few thousanths too large, and then shut the machine down, with part still in the collet, for the night, and come back tomorrow to re-measure and make my finish cuts. Why? Because all that rough work has caused not only the workpiece to warm up, it caused the collet, spindle, bearings, etc., all to warm up, and henceforth, my measurements, although correct, will be wrong when the part is at OPERATING TEMPERATURE. By allowing it to cool to shop temperature, I can be assured that the air-bearing of a 130,000rpm air-bearing cut to an OD of 1.8142 at 68F will fit inside a bore ID of 1.8146" at 68F, and have .0002" float distance under pressurized air...]
- Abide by the thread lubrication instructions. If a factory rebuild spec says torque bolts dry, then DON'T lube the bolts. If they say torque them WET, then apply lubricant.
(I work on engines like McGovern's Chris-Craft KL [marinized Hercules industrial]... and when I reassemble MY industrial and marine engines, I use teflon pipe thread sealant... because it lubricates, seals, and doesn't wash away under chemical attack... and in many cases, head bolts protrude into the water jacket, which means they're a pathway of opportunity for a leak...)
Once you torque a head, it needs to be retorqued. On my Buick 455s, I retorque them THREE TIMES... initially, then walk away for a day, come back, back 'em off an 1/8 turn, torque again, and next day, repeat. On flatheads, I torque them, then run the engine for 5 minutes, shut 'em down for two, and retorque them.... then run 'em for an hour, let 'em cool, and torque them again. Why?
When you torque a bolt, the bolt 'winds up' like a spring. The threads turn for SOME, but not ALL.
When you apply TENSION to a bolt, it stretches, like a spring. Sometimes it YIELDS (deforms). Some do, and some don't. Some head bolts (usually, newer than say... 1980) are DESIGNED to yield... in their design and metallurgy, heat treatment, etc., they STRETCH, so that they apply a predictable pressure as the engine expands and contracts. Imagine replacing a head bolt, with a longer bolt, a pair of washers, and a VALVE SPRING... you tighten the bolt 'till the valve spring is halfway compressed, and at that point, as the engine expands and contracts, that bolt and spring will ALWAYS place the same amount of pressure on the head. Because of this, when a manufacturer says 'use new bolts'... they mean USE NEW BOLTS.
Some engines use STUDS rather than bolts. A stud has a serious advantage over a bolt, namely... if the bolt HOLE is full of crud, or has an incompatable spot in the threads, a BOLT will reach it's torque value, but NOT apply the appropriate clamping force. Let's say the bolt hole is obstructed, and it stops before it even lands flush against the head... you may have 170ft-lbs on the bolt, and it's applying NO grip whatsoever. Next... a STUD is substantially less affected by shank friction as you torque the assembly. When you turn a bolt in a casting, the bolt's shank is contacting the hole. since the hole alignment cannot be 'perfect', there is some amount of contact between the bolt shank and the head... and then the head, which is in contact with the block, will bind. It might bind just a little, and it may bind a LOT, just depends on how tight the clearance is to start with, and how out-of-alignment it is. A stud encounters that friction while the head is slid over the studs, but once down, the nuts spin down, and apply their force to the head, with no additional drag from the fastener. Finally... a head BOLT never engages ALL of the block threads. A stud can thread all the way to the bottom (as long as it's threaded to full depth). A stud will never 'rip out' threads in a block... but a bolt certainly can. Finally, using studs means you can slip the gasket into position, and check it for proper location and alignment, then lower the head in place WITHOUT risking movement (and consequent damage) the the gasket while seating the castings. As a result, studs will generate a more consistent and higher-quality result all around.
Where engines have mix-and-match of studs and bolts, and sometimes, different length bolts, in different positions. it's of utmost importance that one get the studs and bolts in their proper locations.
When I'm assembling cylinder heads that are strictly bolted, I usually make at least TWO studs... I'll find some really long bolts, and cut the heads off... then chuck 'em in my cordless drill and wire brush them REALLY smooth... mebbie even dust them off with flapper-wheel a bit, and thread THOSE into the block, slide the gasket on, then the head... so that my extra-long-bolts are assembly guides for lining up everything nice... so I can see that the gasket is landing properly, that the head seats without skidding the gasket around, and once the head is down, I install most of the bolts, then remove my guide bolts, and install the final bolts.
It may seem a bit excessive, but I rarely have gasket problems with things that I assemble. When I DO have gasket problems, it's almost always a case of bad gasket.
