what happened to my hone???

[Enraged78]

8.5:1 pistons and MLS gasket was used. I thought it seemed low as well. Block was bored .020 and I used ross .020 over pistons. Only thing I think could have been wrong is ring end gaps. What do you think? Would my best bet be to just have it rehoned and pick up a new set of rings and pay extra attention to endgap this time? ( machine shop set gap last time )

I'm actually really curious about this. My machinist and I were going over the endgap of the exact same setup that you have in your car. Ross/Eagle combo with Ross Racing Rings. Ross recommends adding .005 of ring gap for every 30HP per piston increase over stock. Therefore, if you were shooting for 500HP, that would be about 125HP per cylinder, and 75HP per cylinder over stock. Using Ross' calculations, we came up with a gap of .028. We added .003 to err on the side of gap, as what we found later caused us to question the original gap numbers. This brought us to a gap of .031, and it is what we file fit the rings to. Remember that these numbers are when the car is cold, and the gap will close up when the car reaches normal operating temperature. Having too much of a gap is better than too little.

HOWEVER, upon inspecting the original end gaps of the rings (factory pistons), we found that the top ring was touching, which is VERY BAD. When the top ring closes up due to a combination of heat and not enough end gap, you have two major problems. The first is heat from friction. When the ring expands beyond the endgap, the ring is expanding to an area greater than the diamater of the bore. This makes the ring eat into the piston walls, as well as killing itself, and driving up the heat of engine components. It also prevents gasses from passing between the piston rings, and if both number one and two rings do this, the gasses get trapped between the rings, and they cavitate, or "Flutter". This is more likely to happen to both rings because the intense heat coming from the first ring that has expanded beyond it's gap will naturally travel to the second ring. This will do exactly what you are describing.

It will kill the cross-hatch marks prematurely, and eat oil like nobody's business. Double check the end-gap on all your rings. Use the formula Ross gives you with your pistons. If you were running anything over 400 AWHP, you will NEED to be over a .028 endgap, and even that is close.

You can easily see whether or not your rings were closing the gap by looking at the rings. Take the ring out of the piston, and look at the ends where you would file the gap. If they are SHINY, you are touching. If they have some small amounts of carbon deposits, you're generally OK. This is because when you have an endgap, a small amount of gas is escaping past the gap in the rings. When this happens, small deposits get left on the ring ends. Also, check the outer edge of the ring. If it is shiny, and has small scratches in it, it has come into hard contact with the block wall when the ring ends were touching. If it is dull, you're generally OK.

Good luck.

P.S. - Anyone who doubts the use of a torque plate should try a little experiment. Hone your block without a plate, and check it with the bore gauge when it's cool. Now, bolt a torque plate on and check the numbers again. They won't be the same. They will be out or in by as much as .002 inches, and it will vary depending on where in the bore you are. That's enough to cause a problem.


Matt.

 

[Strm Trpr]

That is some excellent information...

 

[1fast97gsx]

yes good info man. I had my machinist set the ring end gaps so I really don't know what they were set to ... I will be pulling the pistons out tonight so I will see if they were touching. I'm pretty sure this is what may have happened. Another thing I noticed is my pistons have a bit of side to side play ( from the intake mani to the exhaust mani ) if I take a flathead screwdriver and give the piston a little push in either direction. They are all like this. Now I'm assuming this is from premature ring wear? Chances are this can't all be fixed by a rehone and a new set of rings with proper gaps this time? I'm shooting for around 450 - 500 awhp ( and should have been putting down 400 when the motor was working last summer ) but I'm assuming all this is somthing as dumb as improperly set end gaps. Hopefully this can be fixed without costing me an arm and a leg.

 

[Enraged78]

yes good info man. I had my machinist set the ring end gaps so I really don't know what they were set to ... I will be pulling the pistons out tonight so I will see if they were touching. I'm pretty sure this is what may have happened. Another thing I noticed is my pistons have a bit of side to side play ( from the intake mani to the exhaust mani ) if I take a flathead screwdriver and give the piston a little push in either direction. They are all like this. Now I'm assuming this is from premature ring wear? Chances are this can't all be fixed by a rehone and a new set of rings with proper gaps this time? I'm shooting for around 450 - 500 awhp ( and should have been putting down 400 when the motor was working last summer ) but I'm assuming all this is somthing as dumb as improperly set end gaps. Hopefully this can be fixed without costing me an arm and a leg.

As far as the piston shift, it will all depend on how much clearance your machinist gave you when he did the hone. My machinist used the Ross specifiactions, and then added .0005 of an inch (half a thousandth) to give it a bit of breathing room. Remember, loose is fast. Forged pistons will expand once the engine gets up to normal operating temperature, as will the rings. Once they expand, they will shift a little less. This initial expansion is what accounts for "piston slap", or something that sounds kind of like a diesel motor when you first start it up. The lower the ambient temperature, the more likely you are to slap. The only way to determine if any damage was done to the pistons, rings, and block is to take each component out, and measure it with a micrometer. Ross gave you a master sheet when they sent you your pistons, use those vaules to determine if you lost any material. As far as the rings go the easiest way to determine their gap value is to take them off of the pistons, and place them into the top of the block's bore. Measure the gap distance with a good micrometer, or if you have to, a feeler gauge. Feeler gauges are less accurate, though. Judging by your power output, you should have had it set to .026-.028 to control the heat AT LEAST. .030-.032 would be optimal, especially if your motor runs hot. Engine break-in also plays a large part in this.

Oh, and my machinist taught me a little trick to help quell piston slap. At the bottom of the piston, you will notice that the skirt is tapered, but the edge is sharp. Use a cookie (air grinder with a scotch-brite type pad) to smooth away the sharp edge at a 45 degree angle. That way, when the piston does slap against the cylinder wall, it won't gouge it.

Hope this helps, and hope my explanation makes sense. I'm still learning how all this works, and luckily have a very good teacher.

Matt.

 

[bastarddsm]

I am not saying this is true, but i thought forged pistons are suposed to run a tighter clearance, than say cast or hyperutectic pistons. i thought that this was because of the more controlled thermal expansion, because of the better metalurgy. maybee i am wrong.

but i do remember when i built my motor for my bike which was air cooled and made 2 times the original hp. the wiseco i put in called for less clearance than the stock spec. and stock were cast pistons

 

[tsi20gawd]

I am not saying this is true, but i thought forged pistons are suposed to run a tighter clearance, than say cast or hyperutectic pistons. i thought that this was because of the more controlled thermal expansion, because of the better metalurgy. maybee i am wrong.

but i do remember when i built my motor for my bike which was air cooled and made 2 times the original hp. the wiseco i put in called for less clearance than the stock spec. and stock were cast pistons

Cast and hyperutectic pistons run tighter clearances.
Forged are looser.

 

[Gigaah]

Could the oil be comming from somewhere else like the turbo?

 

[1fast97gsx]

no .. it was smoking out of the exhaust and there was oil on the piston domes. The intercooler piping and throttle body were dry. It was either rings or valve seals. I have a lot of side to side play with my pistons when I push on them with a screw driver so I think the end gaps were not properly set.

 

[half-cocked]

YES THEY ARE! If you are running a cast piston you can get away without it, but forged pistons require the use of a torque plate to prevent scuffing and other cyliner wall damage caused by an incorectly shaped cylinder.
If you want it to last use a torque plate plain and simple.

Even though a torqueplate is a great idea anyway, Ross piston instructions even have directions for use with blocks not honed with torqueplates.

 

[tsi20gawd]

I never said it could'nt be done I said it SHOULD'NT be done that's all