427 so bored 30 over

[shaps]

Am looking at a cobra with a 427 SO bored 30 over.
I have heard from 2 well respected gents that their opinion is luke warm because the most you can bore the motor (safely) would be 40 over. so 1 more rebuild if necessary.
Was wondering if the collective knowledge base here had experience or other thoughts.
Many Thanks!

[bmalone]

.030 is the max overbore on 90% of SO blocks. Sonic testing would tell you if a particular block can go more than that. Sleeves are an option.

[shaps]

Thanks for the quick response.
Apologies, but i am a bit of a neophyte on some of this stuff...
How viable are sleeves? How costly (assuming all else is ok with block)? Or is this just unrealistic?

The ultimate point is, what are the thoughts of buying a car with a fresh rebuild on a 427 30 over. Intent is to mainly drive on street with 1 or 2 track weekends a year. (open track day/driving school stuff).
Again thanks for the info!

[bmalone]

The majority of original blocks you find will likely be at .030--this is not uncommon. If it is a fresh rebuild and it was done right--I stress done right, then I wouldn't worry about it so much. I say that because it is not like you put a lot of miles on the car even over the course of several years.

Sleeves are not terribly expensive, but must be done by someone who knows how to do it.

[K.Wilson]

shaps,
To help put this into perspective; 0.030 inch would mean that 0.015 comes off the cylinder wall at any one point if the bore is done correctly. The paper in the printer at your computer is between 0.003 and 0.005 inch thick, thus the cylinder wall will be about the thickness of four sheets of paper thinner after the boreing process. If the process was done correctly (the cylinder bore followed the original centerline of the cylinder) the change in strength of the cylinder wall is minimal.
I would guess that after the 30 years that this block has been out of production there are more 427 engines out there at 0.030 over bore than at standard bore.
Keith

[chopper]

Keep in mind that nominal wall thickness for the 427 blocks (especially the early ones without the "square cylinders" was only .110 inch to begin with. Taking 0.015 off only leaves 0.095 inch wall thickness nominal. Sleeves are an option. Steve Crist's book recommends no more than 0.030 inch overbore and only sleeving one cylinder per bank. That said, there's at least one 427 block running around out here in AZ which has all eight cylinders sleeved and he says he's doing fine. Critical questions here are whether or not the block was properly checked for cracks and voids (magna-fluxed and sonic checked) and whether the engine was properly assembled.

[Traveller]

RE: Cylinder Sleeves

The general consensus seems to be: If the person/shop who does it has the skill and knowledge, then sleeving is a viable option.

However, once done you'll always have a 427 with a MAJOR flaw.

If you think a .30 overbore is a concern, try selling a block with a sleeved cylinder..........

[Cracker]

Shaps,

I don't have 1st hand experience but having been a 427 SO owner and servicer of one for 9 months now - I have something to share. The fella's are right in that the block needs to be sonic tested for cylinder wall thickness. My engine builder suggest now more than 4 sleeves per block because this can reduce the strenght of the block dramatically. That said it does need to be done right as mentioned before. You haven't mentioned price - but consider machining costs just to be on the safe side of building any FE. My suggestion would buy one of these new Genesis or Shelby blocks and not worry about how long is will last (the Shelby unit is already sleeved and when they wear out - just replace it). Best of luck!

Tony Hull
Cracker

[shaps]

Gents,
Wow. Thanks...
it certainly does seem like .030 is common. guess that is why standard bore block are "special". as K Wilson said these are almost 40yr old blocks... For me in NY, the casting of the block is important due to the emission standards here. While the idea of a new block is appealing, i dont think it wud work. Also, the car in question already has the motor installed, so im trying to do some due diligence as it were.
Should I be concerned about any overheaing issues due to the bore?
Thanks for all the valuable insight... this has been VERY helpful.

[chopper]

I confess to not understanding your last comment. Why would a "new" block not work? Shelby and Genesis are putting out new aluminum blocks, and Genesis is reportedly turning out new iron blocks. Why wouldn't one of them work (apart from the obvious cost)?

[K.Wilson]

shaps,
Overheating is an issue with all FE engines in all Cobra Replicas. If you search the site you will see this is a very common topic of discussion. The 0.030 over bore will have little to no effect on cooling/overheating in a practical sense. Yes, the thinner cylinder wall will transfer heat to the coolant somewhat faster than the thicker wall but the difference would not be measurable.
Keith

[shaps]

Chopper, NY is a funny state. The emissions law exempts blocks prior to 1968 from any emissions test. Think 68-72 all you need is a PCV valve. After that they start doing tail pipe sniffs. I believe the Shelby and Genesis are 200x blocks, hence in the eyes of NY DMV, it would have to pass 200x emissions. good luck, huh?

KWilson: I was thinking about the effect thinner cylinder walls would have on overheating. thanks.
The car in question has an electric fan with full shroud on the engine side (puller). No fans on the outside. Also equipped with an oil cooler. Any thoughts to the overheating potential?
Thanks!

[Cracker]

I could be wrong about this one, but the two little fan in front (pushers) are more for looks than anything else. I upgraded to an aluminum water pump on my FE and have a puller fan attached to the back of the radiator really gets the job done.

[shaps]

Thanks all. Will follow up next week after I see the car, hear the motor, test drive, etc...
What is the range of displacement for a 30 over motor? I figure how much the motor was decked as well as the heads would have an impact, but is there some kind of range like 435-440 cu inches? do u just multiply 427 x 1.030 ?? (thats439.8) - so much for a 427 hahaha..

[rritchey]

Shaps,

I have 2 427 motors, one a SO and one a TO. Both of them are sleeved all 8 holes. I run them hard, race them, street drive them, they don't have any block fill. They were all thin sleeves, and all went in dry (none of the cylinders had to be bored all the way out to the water jacket to install the sleeves). I have no problems with overheating, no problems with water leaking... no problems at all. They both make in the 500+ HP range and both have lots of run time on them. I build and sell 427 and 428 motors, and I kept these blocks and sleeved them like this just to see if what everybody says is true. Both of these blocks were 30 over with significant wear when I sleeved them. I think after having first hand experience with these two, I am not afraid to sleeve any FE in all 8 holes. The sleeves are made of better material than the original block is anyway.

Bottom line is this: Don't be afraid of a block just because it has a sleeve or two. Granted, I have never sold any FE motor with more than 2 sleeves, but that is just because nobody wants them. If any of you guys have a SO block sitting at 30 with rust pits, send it on over - I'll be glad to put it to use!

Now comes the caution: Be sure the machine shop installs the sleeves with a step bore. This means they leave a "lip" in the bottom of the bore to hold the sleeve in place. Also use plenty of the high dollar locktite when it is put in. If they are done correctly, you will not have a problem. Also another tip - if you are having to sleeve a block all the way or maybe you have a slightly worn std. block with 1 or 2 bad cylinders, use BBC 4.250" thin sleeves and build the motor at 4.250" bore (17 over) and this allows another build at 30 down the road. No use wasting the metal if you don't have to.

[Steve R]

rritchey,
I'm curious, what is the wall thickness of the sleeves you mention? (the BBC @ 4.25) Just doing a little thought experiment here. Have you known anyone to sleeve a block to smaller than stock bore in order to preserve block streanth and also to give it an undefined lease on life? I.E. plan to replace the sleeves multiple times during it's service life?
Steven

[shaps]

Saw the car, and heard the motor. Had the guy give me a small test spin. Motor sounded great, but saw a handful of oil drops coming from the bottom of the bellhousing (UGH!).
Question is, rear main seal?
It could be many things, some mundane, like loose valve covers, or it could be the Rear Main seal. Are leaky rear main seals common in these motors?
Thanks

[rritchey]

Steve R,

The sleeves I used are thin (3/32", .09375") wall thickness. I put in the thickness in decimal form so you can see it is basically 100 thousanths thick. This means you have to bore the engine out almost 100 thousanths just to get the sleeve to go in. Actually, let me get my brain in gear - it is early - the 4.25" sleeve is already .017" over std. bore, so you actually have to bore the motor .09375 + .017 = .11075"..... 110 thousanths! And I have insatalled MANY of these sleeves and never bored all the way through the cylinder wall and never had any problems. Maybe I have just been blessed with good blocks.

As for your question about sleeving a 427 block down, some racers used to take SO blocks and sleeve them down to 428 bore for racing. If you use a 3/32" sleeve you don't have much of a step at the bottom of the bore, but then again you don't need much. I guess this would be a good way to be sure your block would stick around for your grandchildren (assuming no rod caps go through the side).

Shaps,

It is pretty common for an FE motor to leak around the rear main seal, but not if it is done correctly. Lots of builders do not excersize the patience to get the rear main in correctly so that it does not leak. There is a trick to it. You can spend about 10 minutes looking it over real carefully and tell if it is leaking at the main or if it is comming from up top somewhere. Another spot notoriuos for leaking is the rear seal of the intake manifold. If the motor runs strong, sounds good (no knocks or rattles), has oil pressure and does not loose water I wouldn't be afraid of it. You should ask him to cut open the oil filter for you - go ahead and buy a new filter and quart of oil for him. Look at the spark plugs too.

[shaps]

Rritchey. Thanks for all the good info.

The motor sounded tight. had good pressure and held its temp very solidly.
My fear is that leaks only get worse, never better. Can check the manifold, dont think the guy wud be willing to open up the filter or pull a plug. specified "no disassembly". little worried about that.

Someone also mentioned there are 2 or 3 plugs on the back of the FE block that can leak if they are not sealed with the appropriate silicone sealant.

[Steve R]

rritchey,
Thanks for the great reply.
What is the outside diameter of the sleeves used to sleeve a 427 down to a 428 bore size? (what is the interferance fit if any?) I.E., I would assume you don't have to weaken the block as much (Bore .110 over) to install them. Is there any down side as far as cooling is concerned if the cyl thickness is thicker than std due to this approach? And finally, do you have any experiance with the late Hemi and sleeves? I have one with a fresh .030 oversize. (no sleeves) one cyl has a nick a few thou deep, 1/4 '' long, almost horizontal in one cyl. it has a smooth edge. is this cyl condemmed, or would it survive o.k.? (it is an 11.75:1 street toy).... I bought it as I describe it. I can post a picture of the nick if it would help. Steven