F Engine Piston Size Question (1 Viewer)

[JustOneMore]

A couple weeks ago the #6 piston in my 40 came apart. I’m ordering new parts to get it back together and just wanted to double check I’m getting the right thing. The build date is 12/71 and it’s the original F engine. The PO had it since new and kept very detailed records. I can’t find anything about the bottom end being worked on. Also from everything I’ve read if they were overbored they would have numbers stamped into the top which I don’t see. So based on all this I’m assuming they’re standard bore but just wanted to double check here before I ordered new ones? Also the broken one I pulled out has the TEQ logo and the number 60011 on it if that helps.

 

[charliemeyer007]

Wow. Usually #5 takes it in the shorts from the brake booster leaking IMHO. What do you think the mileage is on the engine? Maybe a used piston would work. I'd take the hint and start looking at rebuild it or maybe a different engine or swap.

 

[JustOneMore]

Wow. Usually #5 takes it in the shorts from the brake booster leaking IMHO. What do you think the mileage is on the engine? Maybe a used piston would work. I'd take the hint and start looking at rebuild it or maybe a different engine or swap.

I’m really not sure. The odometer readings on the paperwork from the PO skip around depending on what shop was working on it and also at some point the odometer was changed out. It’s always run very well up to this point. I’d say around 100k but that’s a complete guess.

Yeah I agree. The rest of the motor looks great but I actually already a 5.3 I’m planning on swapping in. I’m planning on doing lots of other stuff along with it that though that I’m not quite ready for yet. So while I know it’s not the recommended thing I’m just going to put a new piston in it to keep it going until I can do that.

 

[charliemeyer007]

I understand. How much is a new piston/rings? Can you even buy just 1? I think I have the other 5 from my second engine that lost #5.

 

[JustOneMore]

I understand. How much is a new piston/rings? Can you even buy just 1? I think I have the other 5 from my second engine that lost #5.

I’ve found single pistons from SOR but for the single piston and set of rings it’s more expensive than a full set of pistons and rings from Rock Auto. Rock auto has the full set of rings and pistons for $228 so I was going to do that but I’m not against putting a used one in as long as it’s in good shape

 

[charliemeyer007]

I'd do the $228 Rock Auto set. I'd measure the bores, maybe you could do 10 over with a little reaming/honing.

 

[JustOneMore]

I'd do the $228 Rock Auto set. I'd measure the bores, maybe you could do 10 over with a little reaming/honing.

That sounds good.

And just to confirm it looks like what I have currently is standard right?

 

[Grayscale]

What is the piston diameter? What is the cylinder bore diameter? The specs are in the manual. 3.541 or 3.543 is where they started at from the factory.
How do the cylinder bores look?
What viscosity of oil(s) were used, or is this engine new to you?

 

[JustOneMore]

What is the piston diameter? What is the cylinder bore diameter? The specs are in the manual. 3.541 or 3.543 is where they started at from the factory.
How do the cylinder bores look?
What viscosity of oil(s) were used, or is this engine new to you?

As best I can tell the piston is about 3.525” and the cylinder is about 3.543” maybe getting close to 3.544”.
The bores seem to be in good shape to me.
From all the paperwork I have it’s always had 10w-30 used in it. I was going to switch to 15w-40 on the next oil change since I don’t know about the exact mileage and I’ve seen lots of other people on here use it.

 

[charliemeyer007]

It sounds like standard. I would plan on scuffing the bores to help the new rings seat. Non detergent oil, Let her get warmed up twice, the re-torque the head bolts and check the valve clearances', manifolds. Go for an around town stop and go, a little freeway connector action maybe a drive threw or two, Check the torque again. Then take it on a good long trip several hundred miles, let it cool out, then go home and change the oil and filter.

 

[JustOneMore]

What is the piston diameter? What is the cylinder bore diameter? The specs are in the manual. 3.541 or 3.543 is where they started at from the factory.
How do the cylinder bores look?
What viscosity of oil(s) were used, or is this engine new to you?

As best I can tell the piston is about 3.522” and the cylinder is about 3.54

It sounds like standard. I would plan on scuffing the bores to help the new rings seat. Non detergent oil, Let her get warmed up twice, the re-torque the head bolts and check the valve clearances', manifolds. Go for an around town stop and go, a little freeway connector action maybe a drive threw or two, Check the torque again. Then take it on a good long trip several hundred miles, let it cool out, then go home and change the oil and filter.

Perfect will do. Thank you!

 

[Grayscale]

My understanding is that once the crankshaft bearings and piston assemblies start to wear thin, the piston rings start on a fresh path thru the cylinder bore, they have to because of the slop in the moving parts. If the step that the top piston ring travels over is too much, then it will start to wear out the piston thru the impact of going over the bump. So if this motor is worn in how it spins, it might break-off some of the replaced piston as well.

There are four things that I'd check. What is the crank's main, and rod bearings diameters? Is there an eccentricity? How much does the cylinder bore vary from worn sections to the unused portion, above the top ring? How worn is the piston and piston pin? Ideally, a telescoping gauge is set in the bore, adjusted to the size of the bore, and they are measured with a 3-4" micrometer, or maybe calipers.

 

[rainingagain]

Ok - so how far have you torn this down?

That piston has clear signs of pre-ignition to the point where the head of the piston has eroded to the oil ring. And there are some very questionable score marks on the side that I am guessing match the cylinder bore. That is likely your root cause of the skirt giving way.

And also something definitely was rattling around in that combustion chamber. Did you find the missing pieces of the oil scraping ring?

If you have the head off or have a borescope, what do the other piston tops look like?

What did the rod bearing look like for that piston #6?