pistons rocking in cylinders

[shee rips]

Piston clearance is not measured at the top of the piston- it's normal to have more clearance at the top because the pistons are made that way. They are "cam ground" smaller at the top to allow for more expansion in that area as the piston heats up. The thicker top area of a piston will expand more than the thinner skirt area.

I bore cylinders every day and I can guarantee you yours will need to be bored- you have wear at the exhaust port area that you cannot see as well as wear on the back of the cylinder around the intake ports. If you run a rigid hone through them this will be evident, you will see lots of low worn areas that will be untouched by the hone. Don't use a ball hone (dingleberry hone) those are for lawnmowers.

thanks for the input, its not what i wanted to hear but i guess ill talk to some machine shops

do i get the pistons first and give them to the person so they can bore it to fit the pistons, or do I just tell them to go .020 over and the pistons will fit?

[swrbansheeboy]

buy your pistons and have them bored to match...

[shee rips]

would it be a bad idea to get any old machnieshop to do them, would i be best off sending them to a builder?

ok dumb question but you get the idea :wink:

[FireHead]

Piston clearance is not measured at the top of the piston- it's normal to have more clearance at the top because the pistons are made that way. They are "cam ground" smaller at the top to allow for more expansion in that area as the piston heats up. The thicker top area of a piston will expand more than the thinner skirt area.

I bore cylinders every day and I can guarantee you yours will need to be bored- you have wear at the exhaust port area that you cannot see as well as wear on the back of the cylinder around the intake ports. If you run a rigid hone through them this will be evident, you will see lots of low worn areas that will be untouched by the hone. Don't use a ball hone (dingleberry hone) those are for lawnmowers.

Two things:

 

1.) Cam turning is the process used in piston manufacture. I know that's what you meant, but calling it cam grinding might lead some one to think there is grinding involved. The last time I ground aluminum was when I was about 8 years old, which was then quickly followed by the first time I ever replaced a grinding wheel.

 

2.)I think there are alot of highly recodnized racing engine programs that would argue that a ball or brush hone are not just for lawn mowers and that fixed ston petal hone are for lawn mowers. IMO you need to have the proper hone for what you are trying to do. If you are trying to crudely remove some taper from a bore or repair some bore damage then go nuts with a fixed stone hone, otherwise gor for the brush or ball hone. :geek:

[FireHead]

would it be a bad idea to get any old machnieshop to do them, would i be best off sending them to a builder?

ok dumb question but you get the idea :wink:

It depends on the builder I suppose. Many automotive oriented machine shops can do an excellent job, but really need to give them a once over before giving your business to them. FOr example if ther are doing their boring on a glorified drill press and they call it a mill, then you need to keep looking. :biggrin:

[blowit]

Piston clearance is not measured at the top of the piston- it's normal to have more clearance at the top because the pistons are made that way. They are "cam ground" smaller at the top to allow for more expansion in that area as the piston heats up. The thicker top area of a piston will expand more than the thinner skirt area.

I bore cylinders every day and I can guarantee you yours will need to be bored- you have wear at the exhaust port area that you cannot see as well as wear on the back of the cylinder around the intake ports. If you run a rigid hone through them this will be evident, you will see lots of low worn areas that will be untouched by the hone. Don't use a ball hone (dingleberry hone) those are for lawnmowers.

 

 

I would respectfully disagree on the ball hone statements. True, they could never be used to make a hole round again but they are worth their weight in gold for two strokes. I do agree that running a rigid hone a couple times will tell the story of highs and lows. The flex hones also help to blend ports and smooth any roughness left by a rigid hone.

 

 

Brandon

[IRONDOG]

Two things:

 

1.) Cam turning is the process used in piston manufacture. I know that's what you meant, but calling it cam grinding might lead some one to think there is grinding involved. The last time I ground aluminum was when I was about 8 years old, which was then quickly followed by the first time I ever replaced a grinding wheel.

 

2.)I think there are alot of highly recodnized racing engine programs that would argue that a ball or brush hone are not just for lawn mowers and that fixed ston petal hone are for lawn mowers. IMO you need to have the proper hone for what you are trying to do. If you are trying to crudely remove some taper from a bore or repair some bore damage then go nuts with a fixed stone hone, otherwise gor for the brush or ball hone. :geek:

 

Here's two things for you grasshopper...

1) Here's a nice link to explain the term "cam ground" that you are not familiar with. Read it and get back to me.

http://www.tpub.com/content/engine/14037/css/14037_103.htm

 

2) You would be hard pressed to find a ball or brush hone in any "highly recognized racing engine program's"

machine shop. The proper way to hone a cast iron cylinder is with a rigid stone hone. Not a cheap spring loaded glaze breaker, I'm talking about a $400 Sunnen hone. A ball or brush hone will not give you the finish you can get with a real hone. About all you get using a ball or brush hone is a warm fuzzy feeling when you mask all the worn spots in your cylinder and it looks all new again when in reality it ain't even close.

I know a little bit about this.

Jerry

www.atvswapmeet.com

[blowit]

Here's two things for you grasshopper...

1) Here's a nice link to explain the term "cam ground" that you are not familiar with. Read it and get back to me.

http://www.tpub.com/content/engine/14037/css/14037_103.htm

 

2) You would be hard pressed to find a ball or brush hone in any "highly recognized racing engine program's"

machine shop. The proper way to hone a cast iron cylinder is with a rigid stone hone. Not a cheap spring loaded glaze breaker, I'm talking about a $400 Sunnen hone. A ball or brush hone will not give you the finish you can get with a real hone. About all you get using a ball or brush hone is a warm fuzzy feeling when you mask all the worn spots in your cylinder and it looks all new again when in reality it ain't even close.

I know a little bit about this.

Jerry

www.atvswapmeet.com

 

 

You basically reiterated my point sir. The rigid hone will not reach into the ports and help smooth chamfering which is why they are preferred by most two stroke engine builders as a final step. There is no question as to its limitations but FAR more useful in the two stroke engines.

 

Brandon

[IRONDOG]

You basically reiterated my point sir. The rigid hone will not reach into the ports and help smooth chamfering which is why they are preferred by most two stroke engine builders as a final step. There is no question as to its limitations but FAR more useful in the two stroke engines.

 

Brandon

A 2 stroke engine builder that would use a ball or brush hone as a last step doesn't have a clue. Why would you want to ruin a perfect cylinder wall finish obtained with the proper hone by going over it with a dingleberry hone in the hopes that you would gain something by smoothing the chamfering?

When I chamfer ports I use a very hard fine mounted stone that I have shaped into a radius that produces a nice rounded edge on the ports. No further smoothing is desired or necessary.

If you feel you absolutely have to smooth the chamfers with the dingleberry hone do it after the boring process but before you do the final hone with the correct hone.

Jerry France

IRONDOG

www.atvswapmeet.com

[FireHead]

Here's two things for you grasshopper...

1) Here's a nice link to explain the term "cam ground" that you are not familiar with. Read it and get back to me.

http://www.tpub.com/content/engine/14037/css/14037_103.htm

 

2) You would be hard pressed to find a ball or brush hone in any "highly recognized racing engine program's"

machine shop. The proper way to hone a cast iron cylinder is with a rigid stone hone. Not a cheap spring loaded glaze breaker, I'm talking about a $400 Sunnen hone. A ball or brush hone will not give you the finish you can get with a real hone. About all you get using a ball or brush hone is a warm fuzzy feeling when you mask all the worn spots in your cylinder and it looks all new again when in reality it ain't even close.

I know a little bit about this.

Jerry

www.atvswapmeet.com

 

1.) Good website article! The thing is, there still isn't any grinding going on. You can call it cam grinding, but that term only comes from the unviversal grinder they used to grind cams with. All modern aluminum pistons that I can think of are turned on a some what specialized CNC lathe or for weirdo one off stuff they are some times milled.

 

2.) Sunnen makes a good hone. If we are talking about well recognized racing programs, you won't find a $400 Sunnen tool you can buy from Napa doing the work. You may find a Sunnen hot bore machine, but that is a $65k investment and you will really only find them in some of your more redneck NASCAR shops. Now, I am not saying there is really anything worng with either method, but I would hate to think that all the engines I have runnign around out there were victimized by $6k a piece ball hones. The thing of it is, on a generic cast iron bore with some taper in it, a Sunnen type hone may be the way to go, but if you do defect free machining, which is what most folks pay for then it is not the best thing to use, in fact, it's not even close. :thumbsup: