951 Piston Protrusion
02-20-2017, 03:25 PM
#1
951 Piston Protrusion
Checking my piston protrusion I note that pistons #2 and #3 are around .012" proud of the deck all around and #4 is less than .01". The issue I'm having is the 1st piston measuring in line with the pin I'm getting .019" towards the back of the engine and less than .006" towards the front. it seems like the piston is kicked slightly in the back but only on #1..How much protrusion is too much? I figure if I'm measuring roughly .02" at the highest point in line with the pin and my commetic gasket is .04" they should never touch even if they are pretty close?
Last edited by mahoney944; 02-20-2017 at 09:00 PM.
02-20-2017, 09:36 PM
#2
If I'm using a .04" commetic gasket how much protrusion is OK from the piston?
And if the piston is kicked it would have to be a fault in the crankshaft, rod, rod bushing, king pin or piston. Since the pin went in normally and 3 of my 4 pistons are fine. I'd say it's the rod or piston that's off.
And if the piston is kicked it would have to be a fault in the crankshaft, rod, rod bushing, king pin or piston. Since the pin went in normally and 3 of my 4 pistons are fine. I'd say it's the rod or piston that's off.
02-21-2017, 03:22 PM
#3
I pulled piston one and gauged everything I could. Piston seems perfect. I believe my rod is bent ever so slightly. The rods I used were from my running engine I tore down to start my rebuild so I assumed they were all OK. Well apparently only 3 were ok 
So new set of rods on the way , not an expense I wanted to add but lesson learned. Luckily nothing was damaged.
So new set of rods on the way , not an expense I wanted to add but lesson learned. Luckily nothing was damaged.
02-22-2017, 08:11 PM
#5
Yeah it probably would not have hurt but I discovered the rod was slightly bent, so I got a set of Carrillo rods on the way. Had the protrusion in line with the pin been close I would have let it go. But couldn't let it go being this far in the build.
02-22-2017, 08:31 PM
#6
Rennlist Member
I would look at the Pauter rods, they will make to any length you want. And if you ever bend one in the future they will make one for you so you do not need to replace the whole set.
02-22-2017, 10:03 PM
#7
Thanks for sharing that info....I have a set of Pauter rods....nothing wrong with them but I did not know that about Pauter if ever i needed that service.
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02-23-2017, 01:17 AM
#8
Rennlist Member
Any competent automotive machine shop can correct rod alignment and twist easily.
.020" piston to head clearance is not enough. You have to consider rod bearing wear, wrist pin bushing wear, oil film thickness, and rod stretch at high rpm. There needs to enough clearance so the piston doesn't hit the head. If you had corrected your wayward rod, you'd have around .028" which is okay. BTW, the stock head gasket is .043"
This is not a guess. I've run them very close for performance reasons - and I've run them too close.
.020" piston to head clearance is not enough. You have to consider rod bearing wear, wrist pin bushing wear, oil film thickness, and rod stretch at high rpm. There needs to enough clearance so the piston doesn't hit the head. If you had corrected your wayward rod, you'd have around .028" which is okay. BTW, the stock head gasket is .043"
This is not a guess. I've run them very close for performance reasons - and I've run them too close.
02-23-2017, 02:49 AM
#9
Any competent automotive machine shop can correct rod alignment and twist easily.
.020" piston to head clearance is not enough. You have to consider rod bearing wear, wrist pin bushing wear, oil film thickness, and rod stretch at high rpm. There needs to enough clearance so the piston doesn't hit the head. If you had corrected your wayward rod, you'd have around .028" which is okay. BTW, the stock head gasket is .043"
This is not a guess. I've run them very close for performance reasons - and I've run them too close.
.020" piston to head clearance is not enough. You have to consider rod bearing wear, wrist pin bushing wear, oil film thickness, and rod stretch at high rpm. There needs to enough clearance so the piston doesn't hit the head. If you had corrected your wayward rod, you'd have around .028" which is okay. BTW, the stock head gasket is .043"
This is not a guess. I've run them very close for performance reasons - and I've run them too close.
02-23-2017, 10:35 AM
#10
Rainman
Rennlist Member
Rennlist Member
Any competent automotive machine shop can correct rod alignment and twist easily.
.020" piston to head clearance is not enough. You have to consider rod bearing wear, wrist pin bushing wear, oil film thickness, and rod stretch at high rpm. There needs to enough clearance so the piston doesn't hit the head. If you had corrected your wayward rod, you'd have around .028" which is okay. BTW, the stock head gasket is .043"
This is not a guess. I've run them very close for performance reasons - and I've run them too close.
.020" piston to head clearance is not enough. You have to consider rod bearing wear, wrist pin bushing wear, oil film thickness, and rod stretch at high rpm. There needs to enough clearance so the piston doesn't hit the head. If you had corrected your wayward rod, you'd have around .028" which is okay. BTW, the stock head gasket is .043"
This is not a guess. I've run them very close for performance reasons - and I've run them too close.
Would you mind sharing your experiences in this other thread?
https://rennlist.com/forums/944-turb...ting-rods.html