Hi Guys,
Another update to the TM scene....
Popped the lid off the beast today, was expecting the worst regarding the valves and wasn't disappointed...Lol...
Here are some pics of the valve seats before and after... This should have been an easter job, it was a resurrection, not a repair...
http://www.warriorpaintball.co.za/private/TM1 Valves and Seats 1700hrs 20160101The inlet valve was fine, no pitting, no major leak spots evident, no corrosion, justnot quite seating 100%, a quick lap with fine valve grinding paste and a nice even contact surface presented itself... The contact area is a tad wide for my liking,around the 3mm mark, I would have preferred a little under 2mm but I wasn't prepared to recut the valve face at this stage...
The exhaust valve and seat on the other hand, was, euphemistically speaking, 'a little worse for wear' .... I am surprised that TM was putting out power, let alone running!
The seat had pitting in excess of .5mm deep, the valve face was pitted likewise...
I refaced the valve at 55/45/35 angles, the 45 being the mating surface.... the valve face is so soft, I simply cut it in the lathe with a HSS tool bit, and not a very sharp one at that.... It appears from the line up of the head face of the valve(around .5mm runout) that our Indian friends had a bent valve and ground it straight... this excessive face grinding has gone right through the case hardening of the valve, or, if it was an induction hardened head, the machining/face grinding has been done sans coolant and caused the sealing face of the valve to soften dramatically.... not a good thing indeed... on my next trip to the specialists, I see a cut and reseat with a decent quality valve coming up....
I expected seat and face damage from the fuel being run, particularly on the exhaust side of things, but not to this degree...(More on this later)
I have managed to do a 'farm style' resurrection, here is how you can do it if you are in a bind:
True up the face of the valve using a lathe or whatever means you have at your disposal... When really stuck, in an emergency, I have used a large drill mounted in a vice or clamp to turn the valve by its stem. Support the top end of the valve stem between two wooden bearing blocks to get it to run as true as possible... while the valve is turning, CAREFULLY use a dremel tool or small grinder to recut the face... Not an ideal way to do the job,but it can be done... In this instance, the soft head was an easy thing to recut in the lathe...
Once you have trued up the valve head as best you can, insert it into the cylinder head and use it, with lots of grinding paste, to recut the seat to match....
After you have a reasonably clean face in the head to work with, you need to recut the valve face again... Try to take as little off the cylinder head as is possible, less is more!
Recut the valve with a slightly steeper angle, 2 or 3 degrees is fine, and relap the valve with fine paste in the head until you have around 2mm of contact width all the way round.... Again, less is more! Too wide a seat, and the chances of carbon deposits fouling the faces increase, too narrow, and the valve can overheat as there is insufficient contact area to draw away the heat to the cylinder head... Be careful of too much paste, you don't want any getting between the stem and the valve guide....
Once all is lapped in, a good wash with parrafin and you are ready to go!
Now, regarding the erosion that is evident, here is what I surmise.....
The inlet valve and seat is in good clean condition, this leads me to believe that the air entering the inlet is clean and of reasonable quality. The water entering along with the air, is having little impact if any either, as there is no corrosion evident, so whatever is occurring is post ignition, or compression...
The exhaust valve is showing effectively all of the beating, so my logic tells me that this is either temperature, combustion by product or steam erosion. I think we can discount stem and temperature by and large, there is not enough of either present I don't think to do this level of damage... This leaves combustion by products... (it cannot be fuel in its liquid or atomised state that is causing it, as there is little to no wear evident on the IP or injector...)
The cylinder upper sections support this theory by and large, but the variables are slightly different, the common factor being combustion residue.
I am guessing, by the wear evident, that the erosion on the exhaust valve face and seat is due to a 'sandblasting' type effect by the residue travelling at high speed as it exits through the valve opening... there is little difference in wear around the entire seat and valve face either, it is fairly even in damage. Deeper into the port, on the botton of the valve guide, there is little to no damage either from a 'blasting' effect, the guide bottom is still nice and square, little bevelling evident either.
This again, leads me to surmise that the particles doing the wear, have to be extremely small, and travelling at an extremely high speed, such as when the pressure is at maximum for a valve open event... ie as the valve open event occurs... as soon as these particles slow down, they lose sufficient of their kinetic energy to do damage, hence the lack of damage on the face of the valve stem guide.., the gas has already started to slow at this point, and is no longer 'jetting' through a narrow opening.... If somebody has a better idea or explanation, feel free to express it, any theories are interesting to me! (Of course, it could also just be a crappy exhaust valve that is so soft it is being impregnated by clamped particles and wearing the faces out...)
If I think of any other bits and bobs I noticed, I will edit this post and update it....
Keep it spinning....
Regds
Ed
