Camshaft Question

[davbell22602]

Now that makes no sense. It's .035 over all together which tells me, that is almost a new bore, but yet it has a ridge?? Am I the only one not following here?

Yes theres a little ridge at the top where the piston stops at TDC.

 

[davbell22602]

The piston diameter is 4.077. I got 4.080 when using a telescopic gauge and micrometer for the inside diameter of the cylinders.

 

[crazy4offroad]

What C4 is saying, is it doesn't need bored.

That's not what I'm saying at all. It is already an 0.030" overbore. It has 0.005" out-of-round/out-of-taper which is out of spec 0.002". IMO I think he can go to 0.040" over instead of 0.060".

 

[davbell22602]

That's not what I'm saying at all. It is already an 0.030" overbore. It has 0.005" out-of-round/out-of-taper which is out of spec 0.002". IMO I think he can go to 0.040" over instead of 0.060".

I get what your saying. Anyways the bore cost and engine kit is the same price for .040 or .060.

 

[crazy4offroad]

You'll only be able to do one more bore after 0.060 which is why I would find some other place.

 

[HotRodPC]

OK, so now you're talking about the out of round. I wouldn't even worry about that it's so minimal, chances are its not from wear, it's probably from torquing the heads. For those who aren't aware, most motors will have cylinders go out of round a bit during break in period. Only way to get around it is to use a torque plate when you have block bored, and they usually charge about double to do that. What a torque plate does, it mimic the bolting down of your heads. So put this peice of thick steal over the head surface with big enough holes for your bores and the bore tool to get into, then they torque this plate down using your head bolt holes to the specified head bolt torque, maybe even more. This should pull the cylinders out of round as if you bolted the heads on, then they do the boring of the block. This ensures your cylinders will stay round after you'd bolted your heads on. It's an added expense but for high dollar motors, or race motors you should do it. Trick is, is to finding a shop that even knows what the hell you'll be talking about and if they have the torque plate for your motor.

 

[Stroked]

^Never heard of that before. Interesting

 

[HotRodPC]

^Never heard of that before. Interesting

You can bet, Nascar motors, funny car and top fuel motors etc, are bored using a torque plate cuz those little tiny thousandths of out of round do matter in those motors. Doesn't matter much to a stocker cuz it's so minimal. But, that's what I'm saying in this case, the little bit out of round is probably normal and I woudln't bore a block just cuz of that.

 

[davbell22602]

Ok, Next question. The pistons are 4.077 diameter. Will have any issues using 4.080 diameter pistons in the cylinders? Or am I better off matching the old piston diameter the new pistons. Any chance of me gaining that .003 when honing the cylinders?

 

[crazy4offroad]

I think you would be better off having it bored. Imagine you're using your cylinder hone to "cut out that 3 thousandths". Well at the same time you're cutting out on the areas that dont need it, that are already borderline.

 

[davbell22602]

Ok. If not ill just find 4.077 diameter pistons. Just means the build will cost more.

Sent from my Milestone X2 using Tapatalk 2

 

[HotRodPC]

The safe bet is have it bored, but if you've measured correctly, I'd rock with a rering and consider it new. .005 isn't much at all, and the bit of out of round isn't enough to justify a bore IMO, but then you speak of a ridge and that's where I get confused and say go for the safe bet and bore it with new pistons.

 

[crazy4offroad]

The high limit, for a smallblock anyway, is 0.004". When I did the re-ring on mine I had a couple cylinders at that max, and now it has plenty of piston slap. Granted I by no means babied the truck, and reused the original pistons but given the chance to do it over I would have went at least 0.010" - 0.020" over to make it right and have a better chance at having a 100,000 mile motor.

 

[davbell22602]

I have to buy new pistons or just the one new that has the crack near the wrist pin hole. I have no problem doing a rering but I'm not comfortable with being that I have no idea how many miles were on it on the 30 over bore when it was pulled and torn apart.

 

[HotRodPC]

OK Great, so now we all agree. Buy the kit that has new pistons and bore the muther fugger and be done with it !!! Sounds as if it will clean up just fine at .040 or go .060 since they also make .090 pistons for the 390, and god only knows, you have, like what 3 390's now? So do as your heart desires. Bore it .090 if want to squeeze all the cubes you can.