Piston question

[Jim Yergin]

As I previously posted, I am in the process of rebuilding the 230 engine in my car because a piston disintegrated and punched a hole in the cylinder wall. I had my machinist check out the spare D24 block I had. After cleaning it up and magna fluxing it, he tells me it is usable but needs to be re-bored. He says it is already at 0.060 over. I couldn't find any 0.070 over pistons but I see that Egge sells 0.080 pistons so I assume that it is OK to go that far over. Other than limiting any future re-bore, is there any reason for concern about going to a 0.080 over re-bore?

Thanks.

Jim Yergin

[Niel Hoback]

Bigger is Better.

[1949P17BC]

Jim, I am sure you go to 90 if needed. Odds are good that motor will out last all of us

[Young Ed]

Jim you better have a chat with your machinist again. He should be able to tell you if there is enough thickness for .080 over. Also keep in mind it usually takes .030 to clean up these bores. Thats why .030 and .060 are the most common upsizes.

[Jim Yergin]

Jim you better have a chat with your machinist again. He should be able to tell you if there is enough thickness for .080 over. Also keep in mind it usually takes .030 to clean up these bores. Thats why .030 and .060 are the most common upsizes.

Ed,

He told me the problem is some rust in cylinder #4 and that 0.010 would take care of that. But for that one cylinder there would be no need for a re-bore.

Jim Yergin

[Don Coatney]

One issue with going .080" over is the posibility of cooling (actually over heating) issues. Jon Robinson of Desoroland fame has had some cooling issues with his .080" oversized Desoto engine.

Is it possible to sleve your engine?

[alan32433]

I'm like you, I would be a little concerned about going 80 over. No telling how much loss of metal (rust) has occurred on the water jacket side of the bore which could cause your cylinders to be really thin.

This may be an option for you to consider. I've found that standard size NOS pistons can be found really cheap sometimes. I saw a set of standard pistons for my mopar on ebay that sold for $30 several months ago. That's because almost everyone is looking for oversized pistons.

If you can find standard pistons at a really good price, you could probably have your block sleeved for about the same price as the 80 over pistons plus the bore job.

Even if it ended up costing more, you would be back to a standard size and not have to worry about any of the above issues. Peace of mind on that really hot summer day.

[Young Ed]

Wouldn't .080 over also increase that headgasket issue for the siamesed cylinders? I would think if its just the one thats bad it'd be better off to sleeve that one.

[Rodney Bullock]

Hi JIm, What they are saying is very true. One 80 is extreme. The over heating issue. The other thing is these cly are veru close together. In my Studebaker 289 I had 3 cly resleeved. The block is bored 30 over. That piston size is not the norm. I just had alot of work done to my Street rod. What I was told when they took my heads off was that my motor had not been bored. I was very surprized. I thought all hot rods were bored and stoked. I was wrong. This means that the motor has room for future rebuilds. How many cly need to go to 80 if it's just a few bring it to 30 over and I think you will have years of pleasure out of your car. If anything goes wrong you will have to fine another motor or block at 80. What ever you do good luck as always, Jim

[martybose]

My 230 motor is 0.072" over, because when we opened it up it was a worn out 0.060" over. We researched rings and found a metric ring set we liked that would clean the bore, then sent them to Venolia with a standard piston for reference. Several weeks later we received a gorgeous set of forged pistons.

At first I thought that I was proof of the overbore/overheating issue, until several years later I found out how far off my temp. gauge was. Now I know that I don't have a problem.

Marty

[Jim Yergin]

Thank you all for the advice. Obviously I need to have a dsicussion with my machinist. Can some one explain why any 0.080 overbore can cause overheating problems?

Thanks.

Jim Yergin

[norrism1]

Jim, When I rebuilt my engine, cyl 5 and 6 had pitted so badly by rust that I had the shop sleeve both cylinders and was able to use .060 over in all cylinders. Was worth the extra $$ to have both sleeved.

[wayfarer]

Thank you all for the advice. Obviously I need to have a dsicussion with my machinist. Can some one explain why any 0.080 overbore can cause overheating problems?

Thanks.

Jim Yergin

On any engine, overheating can occur when the cylinder walls are thin because the combustion heat transfers too quickly to the coolant rather than being absorbed by the mass of the block. You machinist should have a 'sonic thickness testing tool' (call it what you like) and can measure the wall thickness of each cylinder. Although you can get by with thin 'spots' you really want as much meat as possible. How thin is too thin? I would get concerned when some of the readings are in the 0.185 area, but everyone has a favorite number based on experience.

Gary

[martybose]

On any engine, overheating can occur when the cylinder walls are thin because the combustion heat transfers too quickly to the coolant rather than being absorbed by the mass of the block. You machinist should have a 'sonic thickness testing tool' (call it what you like) and can measure the wall thickness of each cylinder. Although you can get by with thin 'spots' you really want as much meat as possible. How thin is too thin? I would get concerned when some of the readings are in the 0.185 area, but everyone has a favorite number based on experience.

Gary

When we were contemplating my .072" bore, we checked every cylinder at the top, center and bottom of the bore, taking a reading every 90 degrees around the cylinder, for a total of 72 readings. None were less than .200" , and the bores were nicely centered in the casting.

Marty

[Jim Yergin]

Thank you Gary.

Jim Yergin