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  #41  
Old 14-11-2006
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pkcof << holds up a sign from behind a bunker - "91 OCTANE"
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  #42  
Old 14-11-2006
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Charlie << throws a *TESTING REGIME* grenade into bunker.
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  #43  
Old 14-11-2006
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Hey Charlie, I have a mate in the states who is an engine builder/mechanic and IMHO a genius. He has offered the following info.

Quote:
Anyway having owned two KTM 380s (and worked on several) I recognized the decompression port since I believe only the KTM 380 has one stock on dirt bikes.

Couple of notes for your friend's bike based upon my experience.

1. Squish is WAY off on the 380 stock. My 98 was .095 and my 00 was .100 inch. Should be set somewhere around .055 to .060 inch. Eric Gorr did my 98 and Clay from Munn Racing did my 00. Significantly better low speed behavior with the tighter specs and both ran very well on pump fuel.

RBdesign could also correct the head squish.

2. If the owner is still using the NOZX needles it will never be jetted correctly.

3. The head bolts are OEM spec'd for 25 ftlbs of torque. I normally tell everyone to follow the manufacture's specs since I have a idea of what typically goes into developing torque specs. However, in this case, the spec is too high and you are likely to go beyond the yield strenght of the OEM fastener.

Stay in line with the specs of all the other manufactures for this size of fastener (19-21 FT/LBs) used in this application and you will not have any sealing problems provided the bolts are not already stretched.

Seeping head gasket problem? Warped head?

Maybe cooling effects of coolant seepage on one side of piston crown. Doesn't look like O-Ring failure.

P.S. I think it would be very difficult to have the fuel mixture so imbalanced due to porting changes that you would end up with a piston/head looking so lopsided carbon deposite wise.

I think the intake ports are just reflecting a slight wash on top of the piston crown: i.e. as the 'clean' incoming charge sweeps into the chamber it clears some of the 'dirty' coolant/fuel mixture away from the intake port area. It is a little concerning that the spark plug orientation seems to reflect the direct path of the burn as it does - I just contribute this to "chance" though.
Don't know if it's much help but thought I'd ask his opinion anyway.

Cheers,
Trev...
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  #44  
Old 14-11-2006
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Cheers kdxer - the squish and needle issues are well known, haven't heard that one about the head bolts though. Sounds like it might be worth sticking a pressure tester on it at some point, if I can find someone with one that will fit...

kicking compression is 180psi at the moment, fresh rings etc but not started yet.
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  #45  
Old 15-11-2006
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Some more info from my mate.....

Quote:
Just some notes - may be useful may not

.055 - .060 inch clearance between the top of the piston near outer edge and head was the clearance I was referring to. So your friend's bike at .055 inch is close to what my 98 was after head modification.

I did not attempt to measure the squish "angle" of the heads after modifications but did attempt to measure total squish area as a percentage of total piston area. My Eric Gorr head had an 45% and my Clay head a 50% squish band. Both bikes had compression readings in the 145-150 psi at 5000 foot elevation. I did not cc either head but did note the following trivia.

98 - pulled harder right off idle and rev'd higher with EG head verses my 00 with Clay head. Both had JD jetting, SLP power pak, same gearing, Twin air filters, DF reed blocks, and I tried both FMF gnarly and OEM stock pipes with same gas/oil ratio.

Apples to apples?? Differences - 00 OEM PWK carb overbored 1mm, 98 had stock PWK carb: 00 had stock engine cases, 98 I had matched the cases to the cylinder: 98 cylinder had been "mo-power" everywhere ported by EG (which really just looked like 'maybe' a slight clean-up on the port passages - very hard to tell if any material was removed) while the 00 had some porting passage work performed by a local shop by previous owner. Both ran well on pump fuel 91 octane.

IMO both bikes ran extremely well after modifications but in both cases the head mods cost some upper rpms. Not really needed by an old guy running a 380 anyway.


I do believe from the first time I looked at the head there was likely some coolant seepage into the cylinder. Even more so now that I see he runs a plug 2 steps hotter than stock. But I did not see any erosion and wondered if it was not intermittent thermal growth sealing problem related to non-uniform sealing of the head to cylinder interface.
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'98 KDX/KX 200 Hybrid "Tweaked by Terry"


Some people are like slinkys, good for nothing really but you still get a laugh pushing em down the stairs...

The day Microsoft makes something that doesn't suck is probably the day they
start making vacuum cleaners.

Windows95 is a 32-bit extension to a 16-bit shell of an 8-bit O/S originally
written for a 4-bit microprocessor by a 2-bit company that can't stand 1-bit of competition.

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  #46  
Old 15-11-2006
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Reckon you could get him to elaborate on that last sentence mate? Sounds like he's suggesting that when it gets quite hot it's letting a little coolant in? Does he have any suggested ways to test for / correct this?
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  #47  
Old 15-11-2006
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Sure, I'll GBTYS.
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I love GREEN

'98 KDX/KX 200 Hybrid "Tweaked by Terry"


Some people are like slinkys, good for nothing really but you still get a laugh pushing em down the stairs...

The day Microsoft makes something that doesn't suck is probably the day they
start making vacuum cleaners.

Windows95 is a 32-bit extension to a 16-bit shell of an 8-bit O/S originally
written for a 4-bit microprocessor by a 2-bit company that can't stand 1-bit of competition.

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  #48  
Old 16-11-2006
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Some food for thought.

Quote:
Pressure testing is good for identifying a number of problems with leakage - both intake type and pressure lost leakage. On a head coolant seepage problem it may or may not help identify the root of the problem.

There of course a number of possible factors like head warpage, bad O-Ring, foreign matter, etc which can be the cause of the problem. On KTMs, in particular, the bolt fasteners used on the head can contribute to problems of this nature and are generally over looked, or not understood, by many shops performing maintainance work.

If a head bolt(s) has been tightened beyond its yield strength (even once) then the bolts will permanently loose its ability to hold constant tension between the cylinder head and the cylinder even though the head bolt is "tight". Sound confusing???

Different metals and different alloys expand/contract at different rates depending upon a variety of factors. The purpose of the head bolts is to keep relative constant tension/pressure on the gasket or mating surface between he head and the cylinder. As the cylinder heats-up it grows in length. This is at a slightly different rate than the head which is also growing in all three dimensions as it heats up. As the components cool contraction of the materials also take place.

There will generally be a difference in temperature which is always changing between the mated components due to engine load, stream crossings, natural cooling, coolant flow, etc.

Torquing head bolts is designed to stretch the bolts WITHIN A GIVEN LIMIT ( while remaining in the yield strength range for the bolt). This allows the head to be held to the cylinder within a prescribed range of tension. This allows for sealing of the combustion chamber, coolant flow passages, etc.

Summary - If the head bolt has been stretched beyond the bolt's material yield strength (elastic property) the bolt's molecular structure has been changed and the bolt has lost it elasticity. This elastic property of the head bolts is what works in conjugation with the gaskets/O-Ring to keep the engine sealed.

P.S. Ever been tightening a bolt and feel it "give" and you just know be experience that another little nudge will result in a broken bolt? If you have experienced the aforementioned then you have reached or exceeded the "tensile" strength of the bolt. The bolt is elongating/stretching and being pulled apart or tensile failure. The yield strength is usually somewhere in the range of 60-70% of the tensile strength and you cannot "feel" it when it is exceeded.

BOTTOM LINE -The head bolt can still be tightened down to a prescribed torque value and not function as intended. It will be "tight" when torqued down but will not 'grow and contract' with the temperature changes as originally intended by the engine designer. This can lead to coolant seepage, failure of sealing gaskets, etc.
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I love GREEN

'98 KDX/KX 200 Hybrid "Tweaked by Terry"


Some people are like slinkys, good for nothing really but you still get a laugh pushing em down the stairs...

The day Microsoft makes something that doesn't suck is probably the day they
start making vacuum cleaners.

Windows95 is a 32-bit extension to a 16-bit shell of an 8-bit O/S originally
written for a 4-bit microprocessor by a 2-bit company that can't stand 1-bit of competition.

Club Mud #147
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  #49  
Old 16-11-2006
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Might be a good idea to get some new head studs. Shouldn't be too dear and at the worst you can eliminate them causing the issue. Hope the info helps some and good luck...
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I love GREEN

'98 KDX/KX 200 Hybrid "Tweaked by Terry"


Some people are like slinkys, good for nothing really but you still get a laugh pushing em down the stairs...

The day Microsoft makes something that doesn't suck is probably the day they
start making vacuum cleaners.

Windows95 is a 32-bit extension to a 16-bit shell of an 8-bit O/S originally
written for a 4-bit microprocessor by a 2-bit company that can't stand 1-bit of competition.

Club Mud #147
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  #50  
Old 17-11-2006
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Thanks for the info KDXer - I got some new bolts and torqued them up yesterday.
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