stihlboy
Guess who's back
it would vibrate at high speed mainly because it is off balance i'd replace the rod without thinking twice
The rod is press sealed on 66 crank......from what's been posted on other threads, unlikely it's the crank( OR are you referring to the piston pin).it would vibrate at high speed mainly because it is off balance i'd replace the rod without thinking twice
"Could it be the base gasket"?
Well this evening I had a closer look at the base gasket and guess what ?
....... it lines up exactly with / The base gasket is a very tight fit to the 56 mm piston and I don't think the piston is supposed to pass through it.
Underneath the piston I see this ridge - bottom right hand corner.
Anyway, here's what I reckoned possibly happened. Bottom of piston hits base gasket, piston rises and turns (see blue arrows) and piston slaps into hot side of cylinder and scores piston. Other side is less affected because I did not run it too long and it is the cooler side of the cyclinder
I measured my BB piston length and it is 1.601 +/- 0.002" long. The original piston is 1.698" long. There is not much in it as the ridge is ~0.010" deep.***
Interested to read what others think about the gasket being a contributing factor.
New BB kit....hmm.....would not be happy either.
The rod is press sealed on 66 crank......from what's been posted on other threads, unlikely it's the crank( OR are you referring to the piston pin).
Now the jugs off Bob,feel the crank rotation.Does it feel gritty or catching ?
Am thinking slogged out journal/s or bearing.
Good idea!Can these be run w/o a base gasket (use sealant)?
No way do you want to shorten the skirt. It's already too short IMHO. Mine freeports at TDC and opens the exhaust port to the case.
That was the manufacturers "fix" Obviously it wasn't enough to also clear a too tight base gasket. I wonder if future versions will leave a bit more material in the bottom of the exhaust port? You probably have set the cylinder down some and extra muffler opening area. I expect that combination would almost always go together but I would be interested to see what would happen with the base exposed to the exhaust port in combination with a stock muffler opening!
The 066 stock piston descends a considerable distance into the base and defiitly goes below the gasket. I had a hand in one of the original 066BB prototype fitups along with Timberwolf. We used the original gasket but had to grind the inside out to make it pass the much larger OD BB piston. That piston interfered with the ID of the base opening as well as the skirts bottoms hitting the bearing bosses so there was a change made to a shorter piston. Good idea to make sure there is gasket clearance plus a margin of safety as it is a thick and fairly hard piece of steel. They could be run without a gasket as is done in other mods but you have to check squish and bottom clearance very close on any aftermarket items. Good idea to check OEM as well.
I also cannot see any pieces where the piston hits the gasket doing that either. I reckon the piston hits the gasket which then drives the piston against the hot sides of the cylinder and thats what does it. I agree the issue of the original piston having problems in the same area remains. The original piston had rings that were well and truly stuck, the BB had slightly more damage but no stuck rings.Bob I am a little surprised to see the scoring from the gasket interference being hauled all the way up to the top of the piston. Are you sure the piston would have been hitting the gasket before the galling distorted it? Still thinking of the original pisston scoring in the same area so make sure that the gasket problem is the only cause.
Howdy,
Thanks for all the information everyone. We're already on our second batch of third generation kits for the 066. The gaskets in our kits do have a larger ID from stock but, the skirt on that piston should be short enough that it doesn't contact the crankcase or gasket. The exhaust port was raised to accommodate this. I will be passing all of this information on to our manufacturer. Once again I would like to thank everyone for their input. We are trying our best to bring these products around to something people can be proud of selling, and using. There a lot of information flying around now, and I'll try to address all of the issues the best I can. If I leave something out, or forget something, please drop a post to keep me on the straight and narrow.
GrandeDog is listening and takes care of his customers.
Has anyone tried the newest 3rd generation kit yet?