Engine block thread clean up

flathead47

flathead47

Member
Getting ready to inspect and cleanup my spare flatheads ..... I understand the head bolt / stud threads are to be cleaned using a thread chaser or modified bolt due to a friction fit.
What about the cleaning the other bolt threads in the block , thread chaser or normal tap.
 
Being these are just storage blocks. Why chase them?

I believe you want a rolled edge chase on headbolts. The rest are okay to my limited knowledge.







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I only have normal taps , was going to get only the chase taps I needed.
Are there different types of chase taps?
Tinker , I have complete motors , partial blocks & want to determine which are useable , thought I would clean all the threads on the good blocks.
First flathead disassembly for me , hope the head bolts come out with no problems.
 
flathead47 said:
I only have normal taps , was going to get only the chase taps I needed.
Are there different types of chase taps?
Tinker , I have complete motors , partial blocks & want to determine which are useable , thought I would clean all the threads on the good blocks.
First flathead disassembly for me , hope the head bolts come out with no problems.
Click to expand...

Bolts or studs? Do not rush either for broken ones can spell a lot more work down the road.

Heat, penetrating oil, and patience make all the difference in the world. Spent 15 hours getting the studs out of a 99A block. Sucks, but got them after trying multiple approaches.
 
Studs & bolts , 1 motor has 2 broken bolts , that's how I got it , already have penetrating oil on the bolt heads .... hoping the rest will come out with out breaking.
 
You may wish to check for cracks & magnaflux first if you haven't already done so. Save yourself a lot of work.
 
For the rest of the threads first screw the pertinent bolt into the threaded hole. If it goes in easily,don't mess with it. I don't think it's a good idea to mess with the main bearing cap holes.
 
Using a threading tap instead of a chasing tap, can result in damage or loss of the threads in the block. The cast iron is usually very soft from the annealing effect of years of heat/cool cycles, and easy to strip.
 
I recall reading that the threads were not tapped to the bottom of the hole. There was a slight lip left somewhat like a pipe thread to help make a water seal on those studs that went into the water jacket. The differential center section was the same way to help make an oil seal at the bottom of the bolt.
 
The Master Cylinder said:
I use the same thread chaser set as 35fordtn. It has both fine and course threads
Click to expand...

I checked this out on Amazon, and it looks good. I was absolutely flabbergasted at the number of bad reviews that came from people who tried to use them to actually tap new holes and cut new threads. P.T. Barnum was right!:rolleyes:
 
I made mine from a head bolt. Took a 4" angle grinder & cut 3 slots in the threads. Works for me. Just don't go ape & force it, but work it back & forth a little at a time.
 
Thanks for everyone's input & advice.
Tinkers links to some other threads were very helpful as well.
My takeaway from the three threads are , test the thread first with a good used bolt or stud to see how tight the thread is ,
if required clean the threads first using gun barrel brushes & cleaner ,
only chase the threads if they have been damaged by using a chase tap or a modified head bolt with 3 or 4 slots cut into it.
If the threads have been tapped using a normal tap it is not ideal, but thread sealers will prevent leakage & help with stud alignment.
The end result is to keep the threads as close to Ford spec as possible, so take your time & do not rush it.
Ian
 
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