Another vertex ring issue

[Jay Smith]

I’ve always found for every .001” a bore is oversized / honed larger than the desired exact correct bore, std or over bored size you will increase the ring end gap by the geometric figure of Pi or 3.14”so if the bore was at 3.516 “ your end gap should be .019” ( no more) , even bigger bore numbers due to wear or over boreing over what bore should have been will yield an even larger end gap according my experiences ...

Call me Tagg 832 597 2603

Jay

[Tagg]

Jay, I saw you mentioned that formula on one of the other threads about this same issue. I'm unlucky enough to have had my machinist overbore one cylider by exactly .002 compared to the other 5, so I have the luxury of direct measurements. I put a ring in a 3.516 hole & the end gap was .028. put the same ring in the 3.518 hole & end gap measures .032. 2 thou bigger bore-4 thou bigger end gap. Pretty close to your formula though.

[FMP]

If the bore was exactly 3.515 instead of 3.518 that same 0.032" gap ring would yield 0.02257" end gap.

The long way home
0.032"-((2π(3.518/2))-(2π(3.515/2)))

[Tagg]

Agreed. But my piston clearance would be under Merc spec. Does everybody just throw out the Merc specs & build them according to some secret specs I'm not aware of? I'm going by numbers the company that designed this motor published. I I'm getting is "should have known to go outside published specs". I'll get it sorted out.

[FORBESAUTO]

Y’all are really killing me. He’s at 0.028 with .001 extra clearance. Actually if ya look at manual it will read finished bore spec to 3.516, so those cylinders are right in line. Also gives a varience of .003 larger and needs to be bored. If he lost his maybe .001 he is still at .025-.026. But being Mercury pistons call for less, This can’t be right for a totally different brand/ style piston. I got an idea, let’s file a set to .019 gap and when it comes unglued let’s rip Vertex on how their piston/ rings are junk just how people nick named wiseco seizco just because they didn’t run enough clearance and didn’t perform proper breakin. One .size don’t fit all, and just because some are different than others don’t mean it’s not right

[Jay Smith]

Heck the mercury manual tolerance on a hi per motor bore is .006” outta round that’s is rediculious my tolerance on motors I build is a half a thousands out of round and if it’s egged more than that I have a bending mandrill that we sell that a 2.5 bore can be bent within that 1/2 thousands or perfect round I require and you need to make power , I haven’t looked at a Mercury manual in 25 years LOTS of tricks that is not in any manual ...

Jay

[FMP]

Forbes, what do like for clearance on this type of piston and use, 0.005-0.004" ?
I heard of Wisecos that tight and never did anything wrong as a hard repeated dyno mule.

[Tagg]

Funny. I saw that spec early on in this project. Not a chance. If I adhered to that info, I could have reringed this thing & saved thousands.

[FORBESAUTO]

Forbes, what do like for clearance on this type of piston and use, 0.005-0.004" ?
I heard of Wisecos that tight and never did anything wrong as a hard repeated dyno mule.

Never used vertex, but from what I’m seeing they have high silicon content to allow for less expansion and reflects more heat back into the combustion (good for making power, and sounds a lot like Hypereutectic Pistons, which also cause more heat to be on rings) and run tolerances like oem cast pistons. Clearance I run depends on spec from piston manufacturer, (most like the pro v is same as oem being they are cast like oem),how the motor is built and what it’s going to used for. A stocker is gonna get set at min spec, the more compression, load it’s gonna be carrying, it’s gonna get a .001 or .002 added ( to answer your question most hot rod motors with pro v get .005 to .0055, .005 is absolute min. For wiseco forged, mine get .007).
I have built enough engines of all types to know that ring gap is dependent of piston design and you need to know the factor # for that particular piston to multiply by bore size to get desired ring gap. This is the figure we’re missing for these particular vertex pistons. I’m getting a hunch since I know of six sets from two recent threads that all gaps are supposedly too big (guessing they’ve tried more than one pack of the complete set, that they are similar to the characteristics of the Hypereutectic Pistons. Here’s a chart with the ring gap factor numbers so you see the difference between the cast and Hypereutectic Pistons to better explain my point.

[FORBESAUTO]

The misconception of “I ain’t running that big of ring gap or that much piston to wall clearance, it’s practically already wore out”, on pistons that require it, is wrong. What people are missing is that when they are checking it, it is stone cold. So your 0.019 gap on your cast pistons once warms up with its limited heat. Ring gap goes to let’s say .010 in operating temp, now these high ring Hypereutectic Pistons at operating temp is applying twice the temp to rings, and guess what they wind up right at .010 too. Same applies to forged piston wall clearance, yeah they start out loose, but when ya beating on em they just as tight as your cast but a heck of a lot stronger. Tight don’t always mean it’s gonna last longer, you want it as tight as possible for the situation at hand to last, but get it too tight for the amount of heat ya gonna be putting to it and it starts scuffing or butting, it ain’t gonna last long at all.

[FMP]

Is this large gap issue relatively new? These pistons have been on the market a long while, maybe something has changed. Those who use them on a regular basis are suggesting 0.017" gap, a typical value. To hit this a clearance minimum to finish would be needed, sneaking up to it keeping it tight. But if more heat is now soaking the rings by design it's likely giving the man answering phone calls a daily headache. Might not be such a bad idea to just run the design and don't add any extra.

[FORBESAUTO]

That’s the magic question, but we know of 12 piston kits that are all supposedly too big. Either it’s intentional or they got a serious bad run.

[FMP]

Like I said before, a test mule two stroke Wiseco was beat on severely for extended time after a slow proper heat cycling breakfast. The clearance was left under spec to prove the point, nothing went wrong. Proper oil film was paramount. The tester claims that if you could pull the piston out of the bore at the highest stress level of heat and try to refit it in an instant you would discover the piston is larger in diameter than the bore. This occurs constantly under high stress and the only thing keeping it going is the film barrier between sleeve and slug.

[Tagg]

Well I'm glad a few are starting to come around to my way of thinking. The block is right according to Merc specs, piston clearance is right according to Merc. Ring end gap is not right according to Merc specs. If vertex is making pistons & rings different now days that require different clearances, they should let us know.

[FMP]

If the box says 3.515" then that's the limit, measure the piston to confirm. It's not a Merc piston so the book isn't helping much.