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
066 Magnum Big Bore Project
- Thread starter blsnelling
- Start date
Help Support Arborist Forum:
Gentlemen, I think we have a strong candidate.
Remember when I posted, "Could it be the base gasket"?
Well this evening I had a closer look at the base gasket and guess what ?
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
If this is the case then perhaps the supplier should provide a better fitting base gasket in the BB kit, or further shorten the piston.
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.
Your thoughts on this would be appreciated.
Remember when I posted, "Could it be the base gasket"?
Well this evening I had a closer look at the base gasket and guess what ?
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
If this is the case then perhaps the supplier should provide a better fitting base gasket in the BB kit, or further shorten the piston.
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.
Your thoughts on this would be appreciated.
Last edited:
Gumnuts
ArboristSite Guru
- Joined
- Aug 4, 2007
- Messages
- 841
- Reaction score
- 136
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.
Last edited:
Wet1
Addicted to ArboristSite
Can these be run w/o a base gasket (use sealant)?
Well I reckon its as smooth and tight as any good ones I've looked at. I also had 2 mechanics at work look at it briefly today. One guy has done a bit of everything, from chainsaws to ore trains, while the other guy has (re)built around 250 racing 2 strokes MC engines. Both guys reckon the crank is good, one guy reckons the little end bearing is worth replacing but neither of them picked up the base gasket problem. It wasn't until I got home and put my head magnifier on and looked all over the piston/cylinder/gasket that I spotted the little groove in the bottom of the cylinder skirt. I reckon that head magnifier is a great little gizmo for blind people like me.
Good idea!
Crofter
Addicted to ArboristSite
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.
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.
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.
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.
Crofter
Addicted to ArboristSite
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!
Actually that's with a gasket and the port not lowered. Strangely enough, squish is only 0.017" with a gasket too. Barely enough.
On reflection I would not like to run without a gasket as my squish is already 0.021". The BB kit recommends use of a Baileys standard 066 base gasket. They were out of stock so I bought a brand new stihl base gasket. Maybe the Bailey's ones are different. If anyone has both maybe they can measure them?
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.
I had a similiar problem with my 066BB. I put it together stock and ran it for a short time. I pulled it back down to port it and found minor scuffing in the same area as yours. The only damage to the piston was above the ring groove. So I polished it out. There was a tiny amount of transfer on the cylinder so it got cleaned up as well. I did notice a very slight tight spot during the initial assemble and figured that was the cause. I hope the offending area is now down to size and won't happen again. I've run the saw since the fix with no obvious problems One of these days I'll go back in and see how it's doing.
BTW, I also know of another member here that has stuck the rings more than once on a 460BB for no apparent reason. Maybe they'll pipe in and share their findings.
BTW, I also know of another member here that has stuck the rings more than once on a 460BB for no apparent reason. Maybe they'll pipe in and share their findings.
Lakeside53
Stihl Wrenching
I also doubt the gasket theory as the source of your damage, but you sure can't use the stock gasket with that piston. Going back to paper is one possibility, but they do pack out and lead to cracking of the cylinder as the screws get loose (check them regularly), and haven't been used in the 066 for a very long time.
Have a machine shop measure the piston and bore for roundness. If you wade through the 361 BB thread, you see Brad seems to have an "out of round" piston and cylinder and I've heard of others.
Definitely don't shorten the piston - it's a hack and as Brad pointed out, already freeports to get around the crankcase fit problems.
Have a machine shop measure the piston and bore for roundness. If you wade through the 361 BB thread, you see Brad seems to have an "out of round" piston and cylinder and I've heard of others.
Definitely don't shorten the piston - it's a hack and as Brad pointed out, already freeports to get around the crankcase fit problems.
Last edited:
Crofter
Addicted to ArboristSite
Lakeside could you measure how much smaller the stock pistons are in the ring lands than at the top of the skirt. Timberwolf I believe had to take a bit off the ring land area as he noticed more contact there than he liked.
Lakeside53
Stihl Wrenching
I think don't think i have a new piston with me (I'm at home with trackhoe stuff for the next couple of days), but I'll try to get some measures from the old pistons lying around.
Last edited:
Grande Dog
ArboristSite.com Sponsor
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.
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.
Right there is why I'm willing to help test these BB kits. GrandeDog is listening and takes care of his customers. I don't enjoy mentioning deficiencies in the kits. But if we don't, he can't fix them. Are the kits perfect? No. But they're getting better.
Well I have to agree 100% there. I just had confirmation that Baileys are providing me with replacement kit. Clearly they are standing behind their product.
Thanks GrandeDog and Baileys.
Cheers and thanks to all that have commented on this thread.
Martinm210
ArboristSite Operative
I've got one of the Bailey's Woodlands kits I bought in December:
http://www.arboristsite.com/showthread.php?t=84545&highlight=woodland+066
The castings were pretty rough, I've spent alot of time cleaning up the ports and piston, but I havn't run it yet. I've got my last order of remaining parts into my Stihl dealer before I'm complete on the build to run it. I wont have a before/after because my saw was bought as a parts saw and didn't have the top end.
For the price I can't complain, but it's no where near the quality of an OEM part.
I think you'll find the BB kit not much different than the latest OEM castings Timberwold posted about in a 460 and a 660. Besides, the flaws you show in the ports isn't going to kill performance. I still think they're a good value and get a lot of unnessesary criticism. No, they're not perfect, but the price is right and you can work the ports over just like OEM if you want.
