Merc block boring question-HELP!

Jack 34pu

Jack 34pu

Senior Member
The machine shop just called me out to look at my '50 Merc block after cleaning and magna flux. Two cyls have deep gouges at the top (broken rings). They probably will require a .060 or larger bore to clean up. Do I do a clean up bore for the other cyls and sleeve these two or go for a big bore Merc? It will be in a street driven 28pu. (1000 miles per yr +) He also wants to square the block but noticed that some the valve seats on one side of the block stick up slightly - enough you can catch your fingernail on them. They don't look like thicker seats. Two other seats need to be replaced (rust) and he says he removes the old seat and bores the hole larger for an oversized seat. Doesn't trust fitting std seat in old hole. These guys are worrying me as they don't do many flatheads. What say experts and those with an opinion. I need your input before I sink a lot of bucks into this block.
 
First off, find a shop that is flathead experienced. I definitely would not want someone who doesn't know flatheads cutting out any seats. I think that job can go south very quickly if one is not careful. If you're talking about building a .060 over flathead, that ain't no big deal.
 
36Tbird is right. If you've got a crack-free flathead with a few issues, find someone who knows flatheads.
 
For your purposes I would not cut the deck unless there is a problem with it being out of flat or has damage.

The .060 over engine is an excellent choice. Be sure to obtain the pistons before the bore size is finalized.

The Flathead valve seats are at an angle to the deck face. This must be observed when counterboring for seats rings.
 
DO NOT LET ANY ONE BORE FOR LARGER SEATS. These can be simply replaced by driving in new seats. They do NOT require the same amount of interferance fit that an OHV engine does. The flathead takes something like .003 or.005 press fit (this is just a memeory, someone else can correct me) I have also cut oversized hardened seats in a lathe to fit a slightly larger hole... And, the seats are at a different angle on each side of the block, do not try to fix this... Karl
 
You can probably still get the original seats for that at Joblot. I also would not deck unless measured beyond spec, and would not allow machinest to tap the stud holes either. Unless badly damaged, those should be cleaned with solvents and gun cleaning brushes. The tight fit will be destroyed by normal class 2 tapping. Tell the machinest that if your studs wobble, you will shim the threads with his scalp.
 
I guess i got some scars on the deck removing the one difficult head. They want to clean it up and square it to the crank. How much would be too much? .005 -.010? Is squaring to the crank real important on this old block. It surely has put in a lot of miles the way she is.
 
As all here stated, find a person/shop that knows flatheads. You will save money, time and lot's of headaches. Thew will know what's enough, and what's too much!
 
do not get the pistons till boreing is done lets say you buy a set 060 now they bore & hit an eye brow & have to go to 70 to clear it what are you gona do with the 60,s never buy pistons till boaring is done.if the seats are higher that says some one has changed them in the past try hiting the seat with a stone to see if you clear the pits
 
Please don't ever try to finish bore a block until the pistons are measured. Therefore it will always be necessary to have the intended pistons on hand before the boring operation is completed.

By careful measuring, select the bore or bores with the worst material conditions and rough bore until it becomes obvious at what size the bores will clean-up. Now, select and obtain the appropriate oversize pistons and get them in hand before finishing the boring operation.

If seat rings are removed using the shrinkage method it is usually acceptable to press in a replacement, stock OD, ring. The rings can easily be removed by TIG welding a tiny, autogenous, bead around the circumference of the valve seat area of the ring.
 
Well Jack, I'm gonna offer my opinion which differs slightly from other comments here. I have always been swayed to a large degree by the thinking of Roger Huntington, author of 'How to hop up Ford and Mercury V8 engines'. He states something along the lines of 'If you need to rebore your block, then bore as big as possible [use good judgement here]. Irrespective of whatever size you bore out to, you'll need to buy a set of pistons. Might as well buy the biggest you can; the added cubes can only be beneficial.'
Although I am not into 8BA series engines; [I prefer pre 48 blocks], it seems to me from what I've read on the internet that 8BA's generally safely go out to 3 5/16". Whilst I am not saying you should go out that big, I am suggesting you shop around, find some decent oversize pistons, get the block bored to suit, and then thoroughly enjoy yourself driving the wheels off of it; you'll never wear it out in your lifetime! Ain't no substitute for cubic inches! Brian
 
we used to drill with a small bit the seat without hiting the block. with the metel removed colapse the seat. when we installed them we packed the in dry ice we did not have all that high teck stuff. but we had skill.my motto the more mods you make the worse they run & the hotter. want a good flathead leave it stock bore as little as possable.i have seven cars you can stand a nickel on the hood & they run all day in hot weather & don,t overheat
 
Jack 34pu said:
Are you saying to weld on the valve seat itself and it will shrink enough to remove?
Click to expand...

I don't presume to speak for JWL, but that's what he means. It's also an excellent method for removing bearing cups in blind holes, or where you cant get a puller behind one.

Bob
 
Before you bore the block find out the available sizes of pistons and then determine where it will clean up .A good shop that bores engines will be able to tell you what works. You should have the pistons to measure before the final bore to determine the sizes for personal shop preferences on clearances. But today's pistons are of a good quality and you should be fine but the machinist will help you out there.
There is nothing special about boring a flatty especially with todays new boring bars .They did it 50 years ago with some portable boring bars and were done okay. The statement find a guy that knows flatheads is good but a competent machinist that can measure and has sound equipment is a wise choice. Think about this the man is in business and a quality job is what they need to produce a top notch product, and have a good product that doesn't come back. Today it takes many thousand dollars to equip a shop. A modern shop today with a serdi, van norman,or rottler bar and others will give you a great finished product. As for cleaning up the deck surface that is a delicate subject with some guy's if it only .005" or so to clean up it can be done but you don't know what was done in a previous life. as the decks are really not that thick to begin with.

Jw's valve seat removal is a great way I have done lots that way they just fall out when they cool off. The story about seats protruding from the block is true but once again if the job is done rite the equipment uses the center line of the guide to determine the data point for machining nothing to do with the deck. All the shops know that be careful to some replies on shop practices. Many replies come from non qualified sources .Just read a few of JWL's statements or Old Ron's you can take their word to the bank. Hence "bin there done that". Others have sound statements also.

Ask for a shop tour a proud owner will give you one and explain the operation look around the shop and see if he is organized and clean you will tell quickly if you feel good about the shop. I hope you get a great job and choose a modern or older established shop that produces a fine engine for you. The statements some have said about finding your parts is a weak one a good shop will secure and provide you with all your parts. That's is what they do rebuild engines not wait around for someone to wander in the front door and say i bought all these parts and want you to do the machine work and maybe put it together and give me warranty. A good shop will stand behind what they sell you not all ways what you provide. Ask about a warranty. I hope this helps you in your engine venture . This is a great new site use it well and ask lots of questions. Let us know how its going.
Sorry for the long post.

Ronnie
 
Please never appologize for a long reply. I'm 68 and still learning. The more detail, the better. This shop has been here for many years but the original owner sold it to the employees. They are young and not as experienced as he was. Squaring the deck worries me the most and I'm to fault as I marked it up trying to remove the one head. The block seems to be virgin (not bored). Not sure how to measure deck height to see if it may have been milled during a previous valve job. The valves look good and may have been replaced but an earlier post say to junk the Ford script valves and guide for new ones. I called a shop in NY and he said most jobs are in the $4 grand and up. That is a little strong for me yet I'm sure he is worth every penny. If the machine work is done correctly, I think I can assemble OK - done lots of Chevy's but this would be only my 3rd flathead and the others didn't have a lot of problems. I wanted Walt Dupont to do me an engine but he is a long way off and pretty busy. Thanks for you input.
 
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