Is P.D.I. seems to be the only co. I can find that has an expanding mandrel that goes up to 2.5" I found one from Enco that goes up to 2", that one would be ok for minis between 65cc- 85cc, but the 54mm 125cc end up being just over 2.12" and needs a larger mandrel,,,,,anyone Bueller?
Precision Devices,,,,the only one?
- Thread starter Jman271
- Start date
Dragmeistr
Sponsoring Member
- Oct 14, 2002
- 149
- 0
Try McMaster.com and look under bore gauges. They have a ton of stuff on their site.
The last top-end I did on my sons RM125 I took the cylinder to my local machinist and he measured the bore with a bore guage within a couple thousandths. I was then able to order a Pro-X piston sized to provide two thousandths cylinder wall clearance. This subsequently has provided us with more compression as well as a longer lasting top-end. :thumb:
So if I were to order the "economy" bore guage set on McMasters, do you all think I can duplicate the measurement given by my machinist when I do a top-end on my YZ or friends bikes?
So if I were to order the "economy" bore guage set on McMasters, do you all think I can duplicate the measurement given by my machinist when I do a top-end on my YZ or friends bikes?
SFO
LIFETIME SPONSOR
- Feb 16, 2001
- 2,001
- 1
Are you looking for a bore gauge or an expanding mandrel?
If you want to really measure bores precisely I would suggest a .0001" reading dial bore gauge.
I have had some success with buying used tooling off of Ebay.
I have also seen good import brands advertised in J&L and Enco for around 200$ that are 2~6" range.
If you want to really measure bores precisely I would suggest a .0001" reading dial bore gauge.
I have had some success with buying used tooling off of Ebay.
I have also seen good import brands advertised in J&L and Enco for around 200$ that are 2~6" range.
EricGorr
Super Power AssClown
- Aug 24, 2000
- 708
- 1
Guys, JMAN is looking for an expanding mandrel that consists of a tapered arbor and a spring steel sleeve. This is used for mounting a cylinder in a lathe so the top and bottom surfaces can be machined.
I bought all my mandrels in the mid-1980s before the Tienamin Squre uprising that led to a whole new set of tariffs imposed on products made in China. If I told you what I paid for my mandrels you'd choke! If I were to buy them today from Precision Devices (the sole importer) they would be well over $2,000.
In the old days I used a face-plate to mount cylinders on my lathe. But it takes a lot of time and patience to true the cylinder in before machining. Also you're limted to machining only the base of the cylinder. The mandrels enable you to machine the top o-ring grooves and straighten out cylinder which have had the bases machined on an angle. Right now I suspect SFO has a cartoon caption with a question mark over his head ;)
Yes you read that right, there are tuners who purposely machine the base of the cylinder on an angle so the cylinder isn't square to the cases. JM Racing in Texas does this and his theory is that theres less friction on the piston during the downstroke because the piston is going down on an angle. I've fixed some of their cylinders which have seized because this cockamamie theory. Another related incident is when a shop bores a cast iron cylinder and clamps in on a hunk of gasket material throwing it off in the boring bar. That happens way more than you think.
Pro Circuit has an interesting set up. They use a CNC lathe with a mandrel that doesn't require a straight through arbor. The technician just slides the cylinder on the mandrel and the arbor clamps to a pre-set pressure from the back side. Precision Devices sells these mandrels also. The advantage to this set up is that programs for cylinder head profiles and cylinder lengths are stored in the machine tool to reduce human error. Thats one of the reasons why they turn down jobs on cylinders and heads that have already been modified. Also they have the luxury of working on mostly new parts, whereas I work on everything in all states of disrepair.
My advice, if you're only going to turn a handfull of cylinders a year, get a faceplate and dial indicator and do it the old fashioned way!
I bought all my mandrels in the mid-1980s before the Tienamin Squre uprising that led to a whole new set of tariffs imposed on products made in China. If I told you what I paid for my mandrels you'd choke! If I were to buy them today from Precision Devices (the sole importer) they would be well over $2,000.
In the old days I used a face-plate to mount cylinders on my lathe. But it takes a lot of time and patience to true the cylinder in before machining. Also you're limted to machining only the base of the cylinder. The mandrels enable you to machine the top o-ring grooves and straighten out cylinder which have had the bases machined on an angle. Right now I suspect SFO has a cartoon caption with a question mark over his head ;)
Yes you read that right, there are tuners who purposely machine the base of the cylinder on an angle so the cylinder isn't square to the cases. JM Racing in Texas does this and his theory is that theres less friction on the piston during the downstroke because the piston is going down on an angle. I've fixed some of their cylinders which have seized because this cockamamie theory. Another related incident is when a shop bores a cast iron cylinder and clamps in on a hunk of gasket material throwing it off in the boring bar. That happens way more than you think.
Pro Circuit has an interesting set up. They use a CNC lathe with a mandrel that doesn't require a straight through arbor. The technician just slides the cylinder on the mandrel and the arbor clamps to a pre-set pressure from the back side. Precision Devices sells these mandrels also. The advantage to this set up is that programs for cylinder head profiles and cylinder lengths are stored in the machine tool to reduce human error. Thats one of the reasons why they turn down jobs on cylinders and heads that have already been modified. Also they have the luxury of working on mostly new parts, whereas I work on everything in all states of disrepair.
My advice, if you're only going to turn a handfull of cylinders a year, get a faceplate and dial indicator and do it the old fashioned way!
- Thread starter
- #7
EG, thanks! You are right! The $600 I would spend now for the expander would not pay off until I did like 100 cylinders, right now this is more of a hobby for my bikes/kids bikes, and helping my buddies out more than anything. I would like to do it more, so if the calling is there, I will go big and drop the bling on a exp mandrel. But, it is also easy to drop off the jug at the local machine shop and tell them what I need done, pay the $45 and have no worries or overhead for machine. They blueprint Harley motors, I have seen their shop, very nice stuff! But, If I lap the deck of the cylinder on my granite plate so it is dead flat, I guess I could bolt it to the face plate w/ dowels or something, then true it up like you said. Angle cut base machining???,,,,hmmmm, sounds very interersting, can you say air leak!!!! Thanks for the heads up, see ya-
Eric,
Not to change the subject of this thread as I see now what an expanding mandrel is used for. But what about cylinder measurment? Will the bore guage mentioned in my previous post above do the job accurately? :confused:
Being able to size the piston to the bore with minimal clearance seems very important for performance and longevity. I'm the type who simply cant accept a stamped letter on the bore as a precursor for piston size. I have to know the actual measurement. Am I being silly?
Not to change the subject of this thread as I see now what an expanding mandrel is used for. But what about cylinder measurment? Will the bore guage mentioned in my previous post above do the job accurately? :confused:
Being able to size the piston to the bore with minimal clearance seems very important for performance and longevity. I'm the type who simply cant accept a stamped letter on the bore as a precursor for piston size. I have to know the actual measurement. Am I being silly?
