More Merc block boring info needed!

Jack 34pu

Jack 34pu

Senior Member
This is a follow up of an earlier thread on boring the Merc block with two gouged cyls. I guess I'm leaning towards a minimum bore and sleeving the two gouged cyls. rather than going to a large bore all around. I want this to be a dependable street driven motor when finished. One reply noted a possible overheating problems with the larger bore. Anyone dissagree? On sleeving, does the sleeve go clear thru the cyl or does it sit on a lip left at the bottom? Where is Walt when you need him??
 
Jack 34pu said:
This is a follow up of an earlier thread on boring the Merc block with two gouged cyls. I guess I'm leaning towards a minimum bore and sleeving the two gouged cyls. rather than going to a large bore all around. I want this to be a dependable street driven motor when finished. One reply noted a possible overheating problems with the larger bore. Anyone dissagree? On sleeving, does the sleeve go clear thru the cyl or does it sit on a lip left at the bottom? Where is Walt when you need him??
Click to expand...

Bore size has almost nothing to do with dependability as long as you don't get carried away.
If you get the block acid stripped you will not have overheating problems
no matter what the bore size. I have had several engines with 3 7/16 bore and they ran as cool as a stocker.
The sleeve sits on a shoulder..Usually about 1/8 inch high.
 
I have never seen a .060 or .080 overbore cause a heating problem. But I have seen some noticable differences at .125 over. From my perspective a .060 or .080 over engine is prefered to a block with 2 sleeves installed by unfamiliar mechanics. Yes, I leave a lip in the bottom of the bore for the sleeve to sit on.

Regarding your questionable deck surface, if it must be machined, look for a shop with grinding machinery. I have seen several shops try to "mill" or "rotary broach" the deck of a Flathead only to do more damage. The cutter will tend to ride-up on the seat rings and leave scallops on the deck. I have seen some shops machine or "sink" the seat rings off below the deck in order to prevent the scallops. Not a good alternative. If there is damage at the gasket fire-ring area, which must be corrected, I suggest using only a surface grinder or , perhaps, a CBN equipped machine.
 
After a couple of engines, I'm convinced that block cleanliness and proper water circulation through the block and radiator are the keys to running cool. Flathead blocks can, and usually do, contain a HUGE amount of rust, scale, foundry sand and other assorted debris in the cooling system. The last block I cleaned out, I got 3 1lb. coffee cans of scale and crud out of the block. Then I got it boiled out. After everything dried out, I dug and scraped almost another coffee can out of the block and this one wasn't running particularly hot. I don't think a 3-5/16" bore will cause you any problem if you THOROUGHLY clean the block and radiator. FWIW.
 
And an .060-.080 bore is practically nothing. It would be crazy to sleeve at that level.
Part of the decking equation is that flatheads, like most production engines, have rather thin decks and you don't want to lose anything unless MEASURED as beyond spec. The valve seat complications add other red flags to the operation...they rarely actually need decking. Machinists like to see shiny on all surfaces and must be stopped when they get carried away! And remember, do not allow them to tap the stud holes...they do that reflexively too.
The bore is only controversial because you are obviously dealing with modern machinists...they are used to SBC and SBF thin wall egines that are so thin they lose power when bored past .030 and are scrap at .060. On a 239 flathead the metal loss at .060 is insignificant. There will be enough left for repeated rebuilds by your grandchildren.
 
The old school machinists used to want to bore the minimum so it could be bored again. I never saw one last long enough to bore again. In the old days, if we paid to bore, we bored 1/8. My flatty is out to 3 3/8, it runs cool.
 
"And remember, do not allow them to tap the stud holes...they do that reflexively too"

Why is tapping the stud holes not recommended? I thought it was common practice to chase all the threads when rebuilding?
 
Because.... the Ford thread is a bit tighter than today's standard. You will lose metal and have a weaker hole, and potentially a loose stud.
 
Just clean them out with something like a brass gun brush and lots of carb cleaner. Properly formed studs will then stand straight up from deck and have more holding power and resistance to leaks. Once tapped, your studs will point all over the place and will be very easy to screw in by hand.
I do not know the history of thread designtions, but it is at least similar to a moden clas 3 thread. Common threads are class 2. Flanks of threads are a bit fatter, threads deeper. A normal tap will magically transform them into class 2.
Be aware that of course MANY engines have already been tapped by a well meaning fixer, including some by me long ago.
Setting up studs: Put your favorite goo from the many recommended here on the threads, screw them into block. Correct force is somewhere in the range from finger tight to 10 ponds torque...studs bottom into their threads and so aren't tightened like nuts against threads. Temporarily drop on your gaskets and heads, put on washers and nuts, and tighten enough (considerably less than running spec) so that the nuts and washers hold everything perpendicular while your goo sets up. This should ideally leave all studs 90 degrees to decks and not binding on holes in heads.
 
You are good to go @ .060" or .080" not a worry at all when done by a good shop and it will be a kool street engine.

Ronnie
 
http://www.gizmology.net/nutsbolts.htm

Here is some good info on threads .Class 3 are usually precision assy not engine head bolts.They should be class 2. If the thread is enlarged you may have used a class 1 tap not to be used for class 2 internal threads. Some good info here.

Ronnie
 
Class 2 will leak and will not hold an original stud tight or vertical without chemical help....not for the decks or for the banjo bolts. I do not know if class 3 was the actual spec used by Ford, but the threads are tighter than the class 2 type fit used on nearly everything else.
According to the Carroll Smith book, class 1 has some crazy spec for parts to be frequently disassembled, and he says that in a lifetime of engineering he never ever encountered a class one fastener or any such taps or dies. For sure they are not used on any common auto application...probably about equivalent to a K Mart nut and bolt from a country you never heard of before.
Class 2, the one that is used on 99% of everything you encounter, has smooth hand fit and allows perhaps a barely perceptible slop between male and female threads before they reach a tight status.
 
Bruce Lancaster said:
Class 2 will leak and will not hold an original stud tight or vertical without chemical help....not for the decks or for the banjo bolts. I do not know if class 3 was the actual spec used by Ford, but the threads are tighter than the class 2 type fit used on nearly everything else.
According to the Carroll Smith book, class 1 has some crazy spec for parts to be frequently disassembled, and he says that in a lifetime of engineering he never ever encountered a class one fastener or any such taps or dies. For sure they are not used on any common auto application...probably about equivalent to a K Mart nut and bolt from a country you never heard of before.
Class 2, the one that is used on 99% of everything you encounter, has smooth hand fit and allows perhaps a barely perceptible slop between male and female threads before they reach a tight status.
Click to expand...

The Ford drawing for the L32 - 34 differential housing specs the 10 holes for the axle housings as follows: "3/8-24 N.F. 3 tap P.D. .3479-.3503" Maybe the 3 in there means Class 3 as we know it today. However, the drawing also uses the same spec for the 6 torque tube holes where a tight thread doesn't seem necessary.
 
I work on Lycoming aircraft engines and there are a lot of studs for these units. They make oversize studs in several sizes of oversize for each original size. They have to go in tight and generally you set them for a particular length of protrusion that is required. In other words they don't hit bottom. If they hit bottom before reaching a certain torque range then go with the next oversize stud.

Too bad they don't make oversize studs for the old Fords. It would help salvage a block that an overzealous tapper got hold of.
 
I sometimes wonder how the old machanics rebuilt these engines60 years ago. I realize new technoligy has made us see things in a different light. Remember these are Flatheads, designed in the late 20's, with a productiion run of 21 years and very little changes were made to the original design. Floating bearings went the way of lock in and studs to bolts. This thread on tapping the bolt holes is another Myth. I also remove the top thread of all the head bolt holes. A flat file will tell you id the deck has any hi spots and Baking the block will clean it well. You'd think you were working on a Fratzeratty engine. If I never worked on a Flathead, and read a thread like this , I never would. Although I've been told that the reason for the SBC was the Flathead was too complicated. Sears sold these for $125, completely rebuilt.
 
Thanks Ol Ron for putting things in perspective. Modern technology does have a way of complicating things that just aren't that complicated.
 
Old Ron

I have called on many high production shops for 25 years and lot of head bolt holes are cleaned out every day with a spiral tap and a cordless drill I don't know where some of the myths come from. I had a customer that was able to do 50 to 75 engs a day without breaking a sweat .They were a ford "reman" production engine re manufacturer . They have to build an engine that meets "ford specs" so they can put an authorized ford rebuild tag on the engine and you can rest assured they couldn't have any come backs or a high warranty claims or you could kiss the approval away.These engines were also distributed through ford dealers. That kind of a repair is accepted as standard practice no deviations or you could not become or remain a Ford reman center which is a very hard title to receive They went through many taps a week just to make sure the holes were correct as they wore out they replaced them on a regular basis . You are absolutely correct about myths and legends of course the taps work. The taps were usually dormer drills and taps from Brazil.Glad you chimed in. I'm reading some posts and thinking where did they dream up some of this stuff.Many of the posters have no idea how some big shops operate. Glad to hear some common sense again.Kill these dumb ideas use common sense . "One more for you".

Ronnie :D
 
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