Two Stroke Cylinder Honing and Oversize Piston Question

[treetopflyer737]

First time posting on here, Hello everyone! :biggrinjester: I'm in the middle of a bottom up rebuild on (2) 787 Rotax motors. I have two questions for some of the more experienced motor builders on here.

1.) Honing. I've been doing my research on two stroke cylinder honing and it seems that there are three methods people use on two stroke cylinders (a flex-hone ball hone, a 3 finger hone, or a nylon brush style hone) with the most popular style being the brush hone (http://www.amazon.com/Wiseco-Nylon-Flexhone-Brush-45-57mm/dp/B0045LB5WC) due to the fact you will not damage the multiple ports found throughout the two stroke cylinder. What are you opinions on these three (ball hone, finger hone, brush hone) on a rotax cylinder? I do not have a large drill press and 3 of my 4 cylinders are going to need deglazing.

2.) Oversize Piston Question. So one of my cylinders has a a nail grabbing scratch on it along with a dry seize area and will most likely need to be bored to remove these imperfections. On a twin piston 787 motor, can you oversize 1 of 2 cylinders to .5mm or will it throw the motor balance off??!! Would my best bet be to have both cylinders bored to .5mm over instead of just doing the one that needs it?

Any help would be appreciated, thank you!

 

[dgoodwin10]

First time posting on here, Hello everyone! :biggrinjester: I'm in the middle of a bottom up rebuild on (2) 787 Rotax motors. I have two questions for some of the more experienced motor builders on here.

1.) Honing. I've been doing my research on two stroke cylinder honing and it seems that there are three methods people use on two stroke cylinders (a flex-hone ball hone, a 3 finger hone, or a nylon brush style hone) with the most popular style being the brush hone (http://www.amazon.com/Wiseco-Nylon-Flexhone-Brush-45-57mm/dp/B0045LB5WC) due to the fact you will not damage the multiple ports found throughout the two stroke cylinder. What are you opinions on these three (ball hone, finger hone, brush hone) on a rotax cylinder? I do not have a large drill press and 3 of my 4 cylinders are going to need deglazing.

2.) Oversize Piston Question. So one of my cylinders has a a nail grabbing scratch on it along with a dry seize area and will most likely need to be bored to remove these imperfections. On a twin piston 787 motor, can you oversize 1 of 2 cylinders to .5mm or will it throw the motor balance off??!! Would my best bet be to have both cylinders bored to .5mm over instead of just doing the one that needs it?

Any help would be appreciated, thank you!

I'm curious to see other's input on honing. I NEED to learn to do this myself.

As far as boring goes, no you can't oversize just one- you need to go ahead and do both the same size. I would encourage OEM pistons on your rebuild- others on here will have recommendations for other brands as well.

You've come to the right place. Lots of good info here if you search and a good group of folks as well.

 

[mikidymac]

You can't hone a cylinder in your own garage. To hone it correctly you are setting up the proper piston to cylinder clearance and know what you are doing.

If everything is good to go and you just want deglaze the cylinders for new rings then a ball hone will be all you need.

The 3 stone rigid hones will be destroyed by the ports in a 2 stroke cylinder.

 

[treetopflyer737]

Thanks for the replies. I have been told by a local motor builder that the .5mm offset should NOT be noticeable however I am open ears at this point!


I am fairly efficient with machinist tools and own all of the proper measuring equipment (Micrometers, telescoping gauges) and plan on honing, chamfering, and setting my piston to cylinder gap in my garage- I've raced motocross and built my two stroke race motors for years without problem.

I've read a lot of information about how ball hones tend to chew up your ports edge chamfers.I have always choosen to scotch brite by hand over honing in the past however I never came across the nylon brush hones before.

 

[ski-d00]

why would you not bore both cylinders? technically, you could bore just one but you'll need to balance the piston weight by removing material from the underside of the heavier piston and do it in the proper position to maintain its own balance. not worth the trouble or time and you'll still end up with an old piston with a shorter life. in car motors, it's fine to do less than all of them and even in the 4tec motors seadoo says you can only bore 1 cylinder. not as simple in two strokes.

if you have a bore gauge and micrometer, you measure and size cylinders in your garage, I do it all the time. a large 3 legged hone works well even on the ports but make sure your grit isn't too aggressive. make sure to chamfer all horizontal port edges. however, if you are boring, you should just have a local machine shop do them for you with the proper clearance, not expensive at all, around $40 per hole.

 

[treetopflyer737]

Looks like I'll be boring both cylinders .5mm over just to be safe without having to shave an extra weight off a brand new piston. Ski-d00 what grit pads do you like to run and how do you finish with the 3 legged hone.

 

[Dr Honda]

You can't hone a cylinder in your own garage. ....................

Hu????

I hone things all the time "In the garage". While you do want a nice, perfect crosshatch pattern... it's really not that critical if it's close.


Now... if you use a proper "Machinist's Hone"... then you can even oversize a cyl in the home shop. But they aren't cheap. Expect to pay a couple hundred $$$ for a basic unit. Along with that... you will need a bore gauge, and an inside micrometer, and VERY good technique to make it happen.

Basically... the cost of the proper tools is WAY more than sending it out to have it done.


But I also second the notion that if you try to use a "Floating" 3 stone hone... you will probably break it. (It will catch the edge of a port)

And lastly... you only want to de-glaze the cyl if you are installing new rings.


Just my 2 cents.

 

[ski-d00]

I don't suggest boring yourself. Just take to your local machine shop familiar with boring 2 strokes or send them off with the pistons to be bored at a reputable 2 stroke machine shop.

I don't recommend trying to hone a cylinder to take .5mm out by hand as you normally will get too much out of roundness and it will take forever even with 80 grit stones. It takes a boring set up like a boring bar to take the majority of the material out and then it is honed to size. Let the machine shop do this for you for $70-$80 for both cylinders, money well spent. Then all you will need to do is thoroughly clean the cylinder with a soft white cloth and new oil and then assemble.

You shouldn't use a ball hone on 2 strokes as it will wash out the ports. You should get a rigid hone like Ammco at a minimum(Lisle hone is better), which are 4 legged, and use plenty of oil. I like to use 280 to get score lines out and then finish with 500 grit. You are looking for a 45 degree crosshatch pattern. If you don't know how to properly use a hone, you can easily catch a port and do major damage.

You sound like you are familiar with machinist tools but this doesn't mean it makes sense for you to do it. I only hone to deglaze or take a couple thousandths out to size up to another piston. While I have a bore gauge and several size micrometers, I take all of my cylinders out to be bored by a machine shop. It's not worth the time or accuracy to do it yourself unless you plan on investing 10s of thousands of dollars opening a machine shop.

 

[mikidymac]

Sorry. Yes you can definitely hone your cylinders at home to deglaze for new rings. What I was trying to say is you can't hone for oversized piston at home. You have to bore them with a boring machine then final hone for the proper piston clearance. Not a typical home job.

 

[treetopflyer737]

To further clarify, I will be having a local shop bore both cylinders .5mm over just so my my mind is clear of any issues regarding the mismatched pistons and my only intentions with garage honing was to set up a proper cross hatch and deglaze for new pistons and rings..

From my experience with two stroke race motors, honing doesn't need to be EXACT on a two stroke cylinder for a two stroke cylinder naturally warps out of round due to the many intake and exhaust ports found throughout after 20+ hours.

Those 4 finger hones are a bit pricey for my liking and I don't like the fact I can take out a port with one and need to order two-three sets of different grit stones. Seems like you need to play around with them for a while in order to get that perfect hone. I ordered a nylon brush hone from wiseco, seems like people are having really good luck with these right off the rip.

I do have one last question, I have been watching youtube videos on port chamfering. 30 degrees seems to be the go to and a lot of people stress using grinding stones or diamond bits (too pricey) over carbide (can chew up nikasil on nikasil coated cylinders and can leave microscopic ridges). I am opting to using some cheaper less aggressive bits like the ones pictured below. Do you guys have any recommendations on which color to use and or another bit for chamfering all together? What is your favorite tool setup for chamfering?

 

[mikidymac]

My favorite tool is the phone. For $99 Group K out of Arizona will bore both cylinders final fit the pistons and chamfer all ports. They have been building endurance race skis since the 90's and know what they are doing with 2-strokes.

Also seadoo cylinders are not Nikasil, just standard iron sleeves in aluminum so you don't have to worry about that.

 

[treetopflyer737]

I am aware that the seadoo cylinders are cast iron and I already have three cylinders that have been bored to spec that need to be chamfered and honed. I plan on doing the chamfering myself, doesn't look all that difficult. I would rather keep it local as far as cylinder work goes, long distance cylinder relationships are costly and have caused some issues in the past due to lack of communication and assumptions.

Any further advice for chamfering with the grinding stone kit I picked up above?

 

[1of500]

The final hone brings them to spec

 

[treetopflyer737]

The final hone brings them to spec

There were bored to a spec allowing me to hone them to cylinder to piston gap spec.

 

[1of500]

I guess you just like to touch everything nothing wrong with that

 

[treetopflyer737]

I had no choice... Bored Cylinders were given to me by a local pwc shop because I help them with a few rebuilds here and there.

 

[treetopflyer737]

Taking MikeyD's advice, I ended up finding a guy local to cleveland that has an awesome report with my motocross racing buddies that does them for $45 a cylinder (bore hone chamfer). The name is Moto Tech and they are located in Mansfield Ohio if anyone is looking in the Ohio area.