Mercury 150 Ring Gap .040 (STD) on honed cylinder within tolerance - is this OK.

[tarponator]

My Mercury 150 siezed a piston. After honing the cylinder (very light scaring) I was left within the specs of allowable tolerances. (STD. = 3.125 +.006 toelrance). The cylinder reads 3.129 with a high quality cylinder dial. <br /><br />The ring gap for this engine is between .018 and .025 max. The other cylinders are within this spec. The honed cylinder has a Ring Gap of .039 which would be out of ring gap tolerance. I'm within spec on the cylinder diameter but slightly out of spec on the ring gap. Do I need to oversize? I already bought the piston based on the cylinder diameter being within spec.

 

[rodbolt]

Re: Mercury 150 Ring Gap .040 (STD) on honed cylinder within tolerance - is this

Re: Mercury 150 Ring Gap .040 (STD) on honed cylinder within tolerance - is this

at .004" over on a worn bore its wore out. no sense in putting it together wore out. but if you do no worries on the endgap its not going to last that long anyway. you may try a different ring in that bore. I have a very diligent machinist I use so I never double check him any more. I do still check ring gaps. its not unheard of to have a mis-packaged or defective one. .004 is a lot on a two stroke. its approaching the absolute service limit.try to exchange the piston and have at least that hole bored. I also still use a feeler gauge between the piston skirt and bore but I really cant remember why .

 

[tarponator]

Re: Mercury 150 Ring Gap .040 (STD) on honed cylinder within tolerance - is this

Re: Mercury 150 Ring Gap .040 (STD) on honed cylinder within tolerance - is this

Originally posted by rodbolt:<br /> at .004" over on a worn bore its wore out. no sense in putting it together wore out. but if you do no worries on the endgap its not going to last that long anyway. you may try a different ring in that bore. I have a very diligent machinist I use so I never double check him any more. I do still check ring gaps. its not unheard of to have a mis-packaged or defective one. .004 is a lot on a two stroke. its approaching the absolute service limit.try to exchange the piston and have at least that hole bored. I also still use a feeler gauge between the piston skirt and bore but I really cant remember why .

 

[tarponator]

Re: Mercury 150 Ring Gap .040 (STD) on honed cylinder within tolerance - is this

Re: Mercury 150 Ring Gap .040 (STD) on honed cylinder within tolerance - is this

Thanks! I agree....

 

[crem1]

Re: Mercury 150 Ring Gap .040 (STD) on honed cylinder within tolerance - is this

Re: Mercury 150 Ring Gap .040 (STD) on honed cylinder within tolerance - is this

Hi!<br /><br />Can you be more specific in how you make all these measurements? I assume that these are expensive micrometers. A novice question<br />Just doing research for a possible honing job.<br />Thanks<br /><br />Alex

 

[rodbolt]

Re: Mercury 150 Ring Gap .040 (STD) on honed cylinder within tolerance - is this

Re: Mercury 150 Ring Gap .040 (STD) on honed cylinder within tolerance - is this

you will need a cyl dial bore gauge and the correct micrometer for setting the gauge. for a rough estimate witin .002 or so a set of telescoping gauges with the correct outside micrometer will suffice. I held plus or minus .001 for years with snap gauges so I have a touch with them. a dail bore gauge does not require much experience to use.

 

[crem1]

Re: Mercury 150 Ring Gap .040 (STD) on honed cylinder within tolerance - is this

Re: Mercury 150 Ring Gap .040 (STD) on honed cylinder within tolerance - is this

Thanks rodbolt!<br /><br />I assume that the bore is not uniformly round(width) at all locations. i.e Top of the bore will be different from the bottom of the bore(ring action on the wall)?<br />Thanks<br /><br />Alex

 

[rodbolt]

Re: Mercury 150 Ring Gap .040 (STD) on honed cylinder within tolerance - is this

Re: Mercury 150 Ring Gap .040 (STD) on honed cylinder within tolerance - is this

most likly<br /> thats why it calls for 9 measurements of each bore. your looking for egg and taper.

 

[crem1]

Re: Mercury 150 Ring Gap .040 (STD) on honed cylinder within tolerance - is this

Re: Mercury 150 Ring Gap .040 (STD) on honed cylinder within tolerance - is this

I'm sorry for hogging your topic tarponator but just one more question. <br />Honing process then just removes 1/1000 of an inch, if not less. The egg shape or taper was made by the cylinder during use or is that what you want to wind up with after honing?<br />Brand new bore is just round(same width) at all locations?<br />So if you are doing a ring job would you automatically do a honing?<br />How do pistons get scarred?<br />Thanks<br /><br />Alex

 

[crem1]

Re: Mercury 150 Ring Gap .040 (STD) on honed cylinder within tolerance - is this

Re: Mercury 150 Ring Gap .040 (STD) on honed cylinder within tolerance - is this

This honing business must be a hell of an art form. The only science is the math(keep measuring the bore to see whether you are within specs). It seems that you have to practice on spare power heads that you don't care what happens to it before trying on your own.<br />Is there anybody out there who actually had no prior experience and tried doing it?<br /><br />Alex

 

[rodbolt]

Re: Mercury 150 Ring Gap .040 (STD) on honed cylinder within tolerance - is this

Re: Mercury 150 Ring Gap .040 (STD) on honed cylinder within tolerance - is this

depends on the hone type, the stones, and the experience of the operator. most ball and flex hones are teats on a bore hog, strictly glaze busters. not reccomended. by the time you remove any marks its oversize most the time, that coupled with the fact that by being flexible the hone will follow the egg and taper of the worn bore. there are some micrometer adjustable rigid hones that can acually bore with, dont ask me how I know . its a loong story but the machinist taught me a lesson that day. the hardest part of honing with a hand held ridgid hone is stroke timing. there are some machine mounted hand activated ones that do a good job and some machine mounted stroke controled ones that do even better.<br /> but yes after boring the bore is mostly round, I say mostly cause it will still have variations just not easily measurable with standard shop tools.<br /> there are tool pushoff considerations and such that will create minute variations.

 

[crem1]

Re: Mercury 150 Ring Gap .040 (STD) on honed cylinder within tolerance - is this

Re: Mercury 150 Ring Gap .040 (STD) on honed cylinder within tolerance - is this

Is there a difference as to how to hone a 2 cycle and a 4 cycle bore?<br /><br />Alex

 

[rodbolt]

Re: Mercury 150 Ring Gap .040 (STD) on honed cylinder within tolerance - is this

Re: Mercury 150 Ring Gap .040 (STD) on honed cylinder within tolerance - is this

depends on what the manufactuer calls for a finnished pattern. but the procedure is the same. the major difference on boring the two is chamfering the burrs left by the boring proces around the port areas.

 

[crem1]

Re: Mercury 150 Ring Gap .040 (STD) on honed cylinder within tolerance - is this

Re: Mercury 150 Ring Gap .040 (STD) on honed cylinder within tolerance - is this

So I gather that the 2 cycle bore is less complex and easier to do. The cross hatch finish that MERC calls for is achieved by any grinding stone or is that achieved by the way or technique that the machinist uses.<br />Thanks<br /><br />Alex

 

[rodbolt]

Re: Mercury 150 Ring Gap .040 (STD) on honed cylinder within tolerance - is this

Re: Mercury 150 Ring Gap .040 (STD) on honed cylinder within tolerance - is this

the crosshatch patten depth will be controled by the grit of the stone, the pattern by the strokes per minute of the hone up and down, 2 stroke bores are more complex due to the interupted cuts at the ports. depending on the wear and accuracy of the macine and the skill of the operator with the boring bar is the determining factor on if the bore ends up correct. I have actually pulled fresh rebuilt blown up motors and seen radial tool marks in the bore that caused the failure. thats why most likly when the machine shop that does my blocks closes I will most likly quit rebuilding them. I just hope I retire before Ron does

 

[crem1]

Re: Mercury 150 Ring Gap .040 (STD) on honed cylinder within tolerance - is this

Re: Mercury 150 Ring Gap .040 (STD) on honed cylinder within tolerance - is this

I'm not sure what you mean by interupted cuts at the ports. Do you actually by-pass the port area or stop at the port? Sounds complex!!!<br /><br />Alex

 

[rodbolt]

Re: Mercury 150 Ring Gap .040 (STD) on honed cylinder within tolerance - is this

Re: Mercury 150 Ring Gap .040 (STD) on honed cylinder within tolerance - is this

as the cutting tip of the boring bar goes round and round while the lead screw feeds it down at a controled feed rate the cutter will pass over the ports. its in the area of the ports that is refered to as an interrupted cut. it can set up chatter and tool push off problems if the setup,cutter or operator is not 100% accurate.<br /> it also tends to roll burrs at the port area.

 

[rodbolt]

Re: Mercury 150 Ring Gap .040 (STD) on honed cylinder within tolerance - is this

Re: Mercury 150 Ring Gap .040 (STD) on honed cylinder within tolerance - is this

http://www.allstates.com/Engine.html#CRANKSHAFT GRINDERS <br /> here is a link to some sites on what some of this equipment looks like. I took my training on most of it, I dont use it now but I have the knowledge even if the skills got rusty.<br /> worked partime in a shop cleaning and sweeping in return for getting taught how to run a crank grinder.<br /> ground my first set of valves and seats on a black and decker machine with a black and decker valve seat cutter. was in the 19th grade and did not even have a drivers license, was cool.<br /> since then I have used a few other makes as they all kinda do the same thing. worst was a modified warner swasy machine cause it was all in mm . problem getting things done now is to do it right and make all the checks as the service manual says is very time consuming and the equipment is not cheap so a lot of steps get skipped.if ya dont belive it next time your in a macine shop ask to see the tool they use to check valve seat runout with.not stem wear but the actual runout of the seat to the stem bore.

 

[danie]

Re: Mercury 150 Ring Gap .040 (STD) on honed cylinder within tolerance - is this

Re: Mercury 150 Ring Gap .040 (STD) on honed cylinder within tolerance - is this

Nine measurements of each bore!<br />"Experts" here do you a favour with three measurements.<br />Rodbolt, wish you lived closer.

 

[crem1]

Re: Mercury 150 Ring Gap .040 (STD) on honed cylinder within tolerance - is this

Re: Mercury 150 Ring Gap .040 (STD) on honed cylinder within tolerance - is this

Since I'm not in your neighbourhood I can't drop off the powerhead and ask you to do it. The question then is this, can an amateur, like me, do a honing job provided he had all the right tools, instructions, and did not exceed specifications?<br /><br />Alex