Just got my cylinders back from the machine shop. It's a speedwerx big bore cylinder at 85.5mm with R&D dominator pistons. I have digital calipers and T gauges but getting consistent measurements down to the .01mm is really tough. I oiled up the cylinders and tried to slide the piston through the bottom of the cylinder and noticed it binds up a little. Enough that the piston won't actually slide through the cylinder unless I give it a push. Once the top of the piston gets halfways through the exhaust port, it frees up and slides smoothly. That just doesn't seem normal... I would think once that forged piston warms up, it'll just seize up in the cylinder. Is that right though?
Super Jet piston wall clearance
- Thread starter Waternut
- Start date
Unfortunately, that's what they did. The capability of machine shops around here is utterly pathetic and I didn't want to have to deal with shipping it out again. So it was hone it up to size or ship it out, wait forever, and get it shipped back which is a pain in the butt. I asked the guy about the heat of honing and he was adamant that it doesn't get as hot as normal operation and he would wait until the cylinder fully cooled to check the dimensions since even a little extra heat will expand the cylinder.
So what's the fix here? If I take it back and tell them to fix it, will honing it a little further cause the top of the cylinder to be out of tolerance just so the bottom can be in tolerance?
Rickster
Matakana Menace
- Location
- Bay of Plenty, NZ
IMO, you should send it to a proper machine shop... No proper shop would hone a cylinder to the next bore... These clearances are just too close to get it right as you have proof of...
Trying to save a little bit of money will cost you a
load in the long run.Rick
Well, for the record, it was never about saving money at all. I was just paranoid about some shop hundreds of miles away losing one of two 85.5mm R&D dominator pistons left in existence and then I'd be stuck resleeving this engine. My better judgement said don't use them but I talked to so many people that go to these guys for hot rods and drag cars that I figured they should know what they're doing and what can and can't be done. I guess even a genius in 4 strokes can be retarded in 2 strokes.
- Location
- New York Crew
Well nothing against them but in the over 400 four strokes I've built in my days I've never honed one up a size or met any shop owner who has admitted to doing it either.
You now have to position the cylinder so the hone spends more time at the bottom of the stroke and use very light pressure on the stones. This means the stones need to protrude at least 30 percent below the bottom of the sleeves. This will prevent honing it too big at the top.
When you get it back check how much the top and bottom of the sleeves feels clearance wise by using a strip of of paper between the piston and the sleeve. The paper found in newspaper ads is about the right thickness to put one small strip on each side plus you can compress it a little as you squeeze the piston through.
Don't you just hate it when a killer machinist does this and then says it is OK and you don't know what you are talking about and maybe even tell you it is supposed to be that way because there is more heat at the top. A good machinist will account for this as they hone it and measure the clearance both at the top and at the bottom and adjust the hone depth or stroke.
Good luck.
When you get it back check how much the top and bottom of the sleeves feels clearance wise by using a strip of of paper between the piston and the sleeve. The paper found in newspaper ads is about the right thickness to put one small strip on each side plus you can compress it a little as you squeeze the piston through.
Don't you just hate it when a killer machinist does this and then says it is OK and you don't know what you are talking about and maybe even tell you it is supposed to be that way because there is more heat at the top. A good machinist will account for this as they hone it and measure the clearance both at the top and at the bottom and adjust the hone depth or stroke.
Good luck.
Rickster
Matakana Menace
- Location
- Bay of Plenty, NZ
Are you serious? You would actually do that? The machinist just
ed up and you want him to do the other side? wowSend it to a proper machinist, which will probably put it through a verticle boring maching and will make sure the clearances are correct.
Then your rare pistons can be put to good use. BTW, I have a good set of used 85.5 pistons in my garage, so they migh not be as rare as you think..
:sneaky:
At this point I assume the clearance is correct at the top and more than likely at least close enough near the ports. Most machinist would not risk putting a boring bar through it because you have to center on what you have as a bore plus you still have to hone it. We are talking taking 2.5 thou off the bottom area only on each side in both the boring and the honing process. If you mike it correctly you will see the taper and you should be able to correct it by honing as long as it is just a taper and not an out of round as well. I am not saying it will be perfect but if you can't find the famous flat top pistons I think it will be fine since we are talking about the bottom of the sleeves there is no ring sealing here, we are talking clearance for the expanding piston skirt only. It sure beats the alternative to resleeving and finding a set of those pistons at a pretty cost.
- Location
- Near Seattle WA
Simple way to check the bore.
The ring end gap should be between .0012" - .020" thruout the bore..
Position the ring in the bore, and slide the piston in to square it up for measurment. Do this in multiple locations if necessary, but it's usually done just above the exhaust port where its most critical.
Its not unusual to hone a few thousands if necessary, but the less you hone the straighter the bore (usually)..
I would find a new cylinder shop... (motorsports machinist).
Regards,
Randy
The ring end gap should be between .0012" - .020" thruout the bore..
Position the ring in the bore, and slide the piston in to square it up for measurment. Do this in multiple locations if necessary, but it's usually done just above the exhaust port where its most critical.
Its not unusual to hone a few thousands if necessary, but the less you hone the straighter the bore (usually)..
I would find a new cylinder shop... (motorsports machinist).
Regards,
Randy
SXIPro
JM781 Big Bore
- Location
- Here on the 'X' mostly
You're in Georgia. Why not have LPW do it for you? He did mine for forged pistons this past summer, and it came out beautious.
x100000. I don't know why we didn't think of Paul first??!! He has been super helpful to me on multiple occasions and is always up for an impromptu help session. He did have some new major project in the works with his real job that was going to possibly make him big time. I haven't heard from him in a few months though. We need to hit him up.
SUPERTUNE
Race Gas Rules
- Location
- Clearwater Fl.
For those who want to know...
25 years ago when building my roadracing RD400's, I had a lot of Sunnen equipment and was having a conversation with my Sunnen field tech with having this problem with power honing 2 stroke cylinders.
His suggestion was to use special stones that were originally designed for honing bores with keyway groove cut into the bores. These stones have a double stone head on each side as well as a double guide shoe head on each side.
They are special order only from Sunnen, but these are the best way to hone 2 stroke cylinders for me.
See pages:
#145 for a pic of the stone sets, the 3rd pic, all they way to the right at the top of the page.
#139 for if you want to use them with a portable hand hone, use a AN-112.
#118 for a GAM/GA-2000 for a very accurate dial bore gauge.
http://www.sunnen.com/graphics/assets/documents/1931f2424f98.pdf
This professional equipment has served me very well for many years with precision results.
Chuck
25 years ago when building my roadracing RD400's, I had a lot of Sunnen equipment and was having a conversation with my Sunnen field tech with having this problem with power honing 2 stroke cylinders.
His suggestion was to use special stones that were originally designed for honing bores with keyway groove cut into the bores. These stones have a double stone head on each side as well as a double guide shoe head on each side.
They are special order only from Sunnen, but these are the best way to hone 2 stroke cylinders for me.
See pages:
#145 for a pic of the stone sets, the 3rd pic, all they way to the right at the top of the page.
#139 for if you want to use them with a portable hand hone, use a AN-112.
#118 for a GAM/GA-2000 for a very accurate dial bore gauge.
http://www.sunnen.com/graphics/assets/documents/1931f2424f98.pdf
This professional equipment has served me very well for many years with precision results.
Chuck