what size is the head stud threads etc for 24 stud v8 merc
 

as per title folks i need to buy some helicoils, what thread size are the studs in the 99A 24 stud units ? i refer to the threads into the block not the nut end

Cheers

Richie

Not sure on the size rich, but the form is UNC (would have been ANC but UNC superceded it) I will go and measure.

Thanks Alastair :)

7/16th UNC
You made me tidy my flathead parts bin too!

Always happy to oblige matey cheers for that

The studs are 7/16 nc
stew

Richard
 

Before you helicoil your block, do some research on sealing the studs. I have read that it is a problem area in flathead v8s.
There is a guy in a Ford V8 forum that goes by the name of "rumbleseat". He has posted widely and is very knowledgeable.

Use one of the liquid PTFE pipe sealants, that will do the trick. Loctite one is good, been using it for years.

Richard F.
 

I would just be a bit concerned about the teflon letting the studs over tighten, causing distortion.
I have read that the piston to bore clearance is markedly different depending on the use(or not) of a torque plate.
Apparently the flatties are weak in this area, and care needs to be taken.
A teflon type sealant with the low friction co-efficient might just force that casting out of shape.
I too have used the loctite thread sealant for years, and find it a magic product. Just not sure in this application.

I posted a topic on the V8 forum and have been advised to TIG weld a washer onto the stud then melt a load of parafin wax around the stud (so it seeps into the stud hole) then weld a nut onto the washer...if i use an impact gun it should spin the stud out.

Richie, Use this method to get them busted off head studs outta your bren gun motor. Instead of the Kroil mentioned in the article, I use a candle. Hold the candle to the hot welded washer/nut arrangement, the parafin melts and flows down the threads better than anything else I've tried. This system works extremely well and eliminates the need for helicoils. Regards, Brian
http://www.fordgarage.com/pages/studremoval.htm

Problem of studs sticking
 

Hi

Richards comment about Problem of Studs sticking/seizing was one I was going to ask about. Though I don't have a Carrier I've worked on a lot of flat heads and will be starting on a flat head project as soon as I finish with my HUP overhaul.

The question deals with why studs instead of bolts?

Lincoln in 1949 changed over from studs to bolts on its big 337 flat heads apparently because of the problem of the heads getting stuck on the studs. I have an early 49 and a late 49 engine getting the head of the early when it blew a head gasket was murder because though the engine would run the side with blown gasket would not create enough compression to break the head loose once all the the nuts on the studs had been loosened. Ended up driving wood wedges in all the way around the head to get it free. The late 49 engine has bolts which come out with an impact wrench fairly easy and once the bolts are out a gentle tap, wooden mallet the head comes off, in fact the problem is keeping from sliding to far.

According to one source the problem heads seizing to the studs was such an issue particularly with aluminum heads (on Hot Rods) that there even were very thin hole saws just large enough to fit over the studs to open up the head holes. Never have found or even seen one of this special saws though.

So to the question why studs? Is it because of concern over wear of the block threads through repeated dis-assembly and assembly for maintenance?

Cheers Phil

You can get a more reliable torque with the studs as the nut end uses a finer thread than a cast iron block can reliably take, the block end is UNC and the nut end UNF. Also back then heads were off once a year for a decoke unlike with modern fuel additives where you don't strip and engine unless there is a failure.