308 over bore?

BillUSN1

Have my 308 block at the shop for boring.

I have one cylinder with rust pits. May be up to .100.

So I may need to decide on sleeve or find a piston that will work.

I have found up to .060 pistons and Randy discussed max of .080.

Any one gone to .100 on these blocks?

My first concern would be hot spots and over heating if the walls get thin.

BillUSN1

Thanks Ken.

Sort of what I'm thinking.

I do have another block but this one had no cracks and is the later with 1/2" head bolts.

Is there a preferred modern piston?

Ol racer

FYI

I think Dale Cooper can get 3 ring Pistons from a V8 Mopar.Tops will have as slight valve depression & may need mill off dome.. Ive gone100 over in the past with no problem,

BillUSN1

Are the new 4 ring pistons, pinned on the rings like the originals? Not a real fan of the originals.

Racer, Do you remember what pistons you used at +.100?

RL Chilton

I have found that most modern-day engine builders are not fans of pinned rings. It seems the vast majority of them do not utilize. 

Frankvintagefullflowcom

Pinned is bad. If Hudsons were a two-stroke engine, it would be mandatory.....but they aren't. I have personally had a pinned piston failure (a new Sealed Power part) and have seen evidence of failures in engines I've dis-assembled. Additionally, I have seen considerable piston damage due to erosion of the ring lands, especially at the upper oil ring groove where there is a direct path into the crankcase. With rings lined up (never considered to be a good idea in any other engine) flaming-hot gases are forced through the gaps with destructive results. (Photos if desired)

My personal opinion is that the rings don't move around so there's no reason to pin them in place, esp. considering the downside. Ported-cylinder engines (like most two strokes) are a different story.

I have a .100 over 308 block here (also @ 5" stroke) that shows no evidence of issues, however I'd agree that some factors will determine how good of an idea that is, like "core-shift" when cast and the severity of corrosion in the water jacket.

Frank

BillUSN1

Frank,

Do you know what pistons are in that?

DavidC

0.100 over is a bit much, can be related to overheating and cracks.  Sleeving the one sounds good if you need to have the original motor.  If not, blocks are pretty plentiful and cheap

Frankvintagefullflowcom

I should have mentioned that an overbore to .100+ presents some challenges regarding head-gasket fit. An increase in cylinder radius of .050 leaves a lot of the fire ring "hanging out" into the combustion chamber. Issues are questionable effectiveness of seal and possibility of detonation due to "glowing gasket syndrome" or GGS. Ask your doctor about GGS.....I'm sure there's a drug for that. Side effects include, impaired vision, vomiting, abdominal pain, pinging...............the standard list.

F

We want to know more about these plentiful and cheap 308 blocks.

BillUSN1

I've read old post about Clifford offering a large bore head gasket but no specifics. And given that the SIL now runs things, there is a lot less available then there used to be from Cliffords.

Jay_G

When Jack built my engine he would only go .60 over.  He told me there were to many issues with going larger than that.  By the way he went through 5 blocks before he found one with no cracks.

Jay

Frankvintagefullflowcom

In a clear attempt to drag this out forever, I thought that I'd respond to Bill's Q about piston make. Since the engine is still largely assembled (sans head) I can only see the top of them so I attached a photo of that. It certainly was someone's toy as is evidenced by the chromed water pump, timing chain cover and tappet chamber covers.

It appears to be in good shape yet with no obvious ugliness. I'd guess that it gave the previous owner plenty of good memories and many miles/hours/laps/passes. Valves are oversize though I find it interesting that the cam shows stock lift. It pencils out to 361 Cu. in.   Too much on my plate to look into it now but I'll get into it eventually.

Also, not to question Ken's comment on the subject, but it shows evidence of having had a stock type head gasket on it as opposed to the copper version. 

Frank