bjorn773
ArboristSite Operative
I made sure of that, nothing crazy, just a gradual arc to help tuck the ring back in. I also tried to make it as symmetrical as possible so it wouldn't make the ring want to rotate.
365 BB Kit
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bjorn773
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Is this more or less what I'm after?
Yes. If you use a more pointed tip, you can sharpen more of it, closer to the edges.
bjorn773
ArboristSite Operative
Is this more like it?
TRI955
I'm the man in the box
That's about what I did to my 7901 BB kit.....
That looks real nice.
bjorn773
ArboristSite Operative
Is this sufficient arch on top of the port to tuck the ring back in or do I need more?
bjorn773
ArboristSite Operative
It looks like my squish is at .029 without a gasket. My only alternative is mill the cylinder, right? I think I will run at .029 for now. I'll seal with permatex aviation form-a-gasket, it says it resists gas and oil.
That looks very nearly flat to me. You'd probably be ok with a good bevel, but I would like to see a little more curve to it. But I also hate to raise the exhaust roof. Can you grab another shot with the piston higher, and the gap even smaller? Leave just a sliver of light. Angles are always distorted in pictures.
stihlboy
Guess who's back
this thread is a porting 101
bjorn773
ArboristSite Operative
I've been going thru AS withdrawal... I hope these are better pics
AUSSIE1
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Is this sufficient arch on top of the port to tuck the ring back in or do I need more?[/QUOTE]
I use a base gasket to read across from the crankcase to the cyl so you can remove any mismatch. Use your gasket, you will see what I mean.
With a small bit, you can get right into the corners to rid the restrictions.
Put a sharp edge on cyl at the transfers.
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bjorn773
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I'm not understanding how that relates to the piston rings into the port here. I assume you're commenting on the previous transfer pics.
bjorn773
ArboristSite Operative
I gotcha, it makes sense after laying the gasket onto the base. You're saying clean out the corners of the transfers to match the gasket and crankcase.
How about this port arch, is it enough?
How about this port arch, is it enough?
AUSSIE1
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I had the wrong picture of yours up at first.
If you use your base gasket as a template, sit it on your crankcase.
You will notice there isn't any material protruding into the gasket area.
If you then transfer the gasket over to the cyl, you will see what material will cause restriction.
The bit of cyl between the cyl itself and the lower transfers can be sharpened.
If you imagine the saw assembled, this area protrudes into the crankcase.
TRI955
I'm the man in the box
bjorn, how bad were the castings on your cylinder?? When I put the 7900BB kit on my Makita the castings were rough but ok, the 372BB kit I just received the castings in the exhaust, intake and transfers look like crap!! It's gonna take alot more on this one to just clean it up to make it useable in my opinion. Back to the old saying, you get what you pay for.....I might just reuse the 365 topend and call it good.
Mike
Mike
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bjorn773
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bjorn, how bad were the castings on your cylinder?? When I put the 7900BB kit on my Makita the castings were rough but ok, the 372BB kit I just received the castings in the exhaust, intake and transfers look like crap!! It's gonna take alot more on this one to just clean it up to make it useable in my opinion. Back to the old saying, you get what you pay for.....I might just reuse the 365 topend and call it good.
Mike
I'd have to say they looked like crap. I still have a couple of pits in the exhaust that are pretty deep. I don't think I could remove enough material to get rid of them. It cleaned up pretty well with a lot of work. You definately get what you pay for. I doubt a couple small pits are gonna make a huge difference. I'm not competing here, just cutting up firewood.
bjorn773
ArboristSite Operative
I've been going thru AS withdrawal... I hope these are better pics
I am sorry to keep beating this horse, but do you think there is enough arch on top of this port to tuck the ring properly or do I need to work it over more?
