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Topic Review (Newest First)
03-23-2010 07:59 PM
Migman Get yourself a thread pitch gauge. Make sure you are using the same pitch bolt as the tapped hole. If the hole is in aluminum make sure the the threads are not galled. If they are use a threadsert or helicoil. I've never seen a clean tapped hole that the correct size bolt would not go in by hand turning only. Something is wrong somewhere. A flash light and a magnifying glass would be a good starting place.
12-19-2009 06:18 PM
Dave5605 Bottom line here is the bolt and the tapped hole are not the same size.
Forget the dremel, forget the drill. Forget drilling out the first couple of threads. YOU NEED THE RIGHT TAP to match the head bolt.

There are a few metric and US threads where if you try to match up mixed nuts and bolts they will SEEM to go together. However they, in fact, are not. The nut is usually a little bigger. I'm sure you can run in to the same scenario with cheap taps and dies. its also easy to thread in the wrong tap in to the existing threaded hole in certain ranges of metric/us threaded holes.

Be very careful that you don't screw up the threads in the block enough that you have to put a helicoil in.

What kind of motor are we talking about here?
Does the bolt screw in to the other holes in the block for the head? If so then its a good chance you have tapped the offending hole wrong.
Also, a real dumb question here, you aren't trying to use some galvanized bolt from the hardware store are you?
12-18-2009 06:30 PM
jagking the thread pitch is slightly larger than the old pitch if not the same.



Thats your problem slightly anything wont work it has to be exactly same !!!
M12 coarse pitch is 1.75 Fine is 1.5 or 1.25
all we really use over here now is metric and i have never seen a M13 bolt its M12 or M14
1/2 whitworth with is the old British standard had 14 threads per inch and a pitch of 1.814 invest in a pitch gauge this will help and wont cost the earth
are you sure that its not 1/2" with is 12.7000mm m12 will pick up in it and allow for the difference in pitch
12-09-2009 12:38 AM
TubeTek Are there any other markings on the tap besides the M12 x 1.75? Maybe something like H11 or D6 or some other combination of letters and numbers. Someone could've sold you a special undersize tap instead of a standard one and they can usually be identified by some additional makrings on the tap shank.
12-07-2009 07:13 PM
hotbrat i have a micrometer; they are the same yes!

Remember I said I ran a Die and nut over the bolt; that verifies the size of the bolt to be what I think it is
12-05-2009 11:47 PM
4 Jaw Chuck
Quote:
Originally Posted by hotbrat
the thread pitch is slightly larger than the old pitch if not the same.
You need to verify the thread pitch and diameter are the same, these are the essentials of any threaded interface. If you don't have a vernier/micrometer you can use a strip of paper wrapped around the bolt to determine circumference. To verify pitch take a piece of paper and rub it onto the threads and compare them.

Metric fasteners often use identical pitches for different diameter fasteners, I think that is where your problem is.
12-05-2009 07:01 PM
gas_guzzler Sorry if I missed seeing it some where, but if you're having trouble with one particular hole have you tried fitting one of your other old bolts that screw nicely into another hole in it?

Sounds really unusual with all the things you've tried.

I don't have a dremil tool so I'd use a proper (and sharp) countersink tool.

Just some ideas, dont mean to offend any one...


Edit: Also did you try a M12x1.75 nut on your tap as mentioned earlier?
12-05-2009 06:37 PM
hotbrat
Quote:
Originally Posted by cucumber1949
That was my experience recently with a SBC. Removed head, cleaned up threads in engine block, and used new head bolts. One head bolt would not start properly with head sitting on the block and dowl pins engaged. Remove head and bolt would start and thread in perfectly into the block. Put head and gasket back on and no luck. I took the head over to the mill/drill and enlarged the problem hole by a 1/16" and problem solved.
the head is off; i do not have the head or head gasket on

Yes I am going right to tighten them. im not an idiot!

the thread pitch is slightly larger than the old pitch if not the same.

The dremel idea sounds like a good idea if I can buy the parts
12-05-2009 08:41 AM
bentwings Uhh are you turning the bolt the right direction.?? "Righty tighty, lefty loosey" for right hand threads.
12-05-2009 08:19 AM
welder4956
Quote:
Originally Posted by hotbrat
m12 is pretty large. the dremel heads are tiny.

How about using a large drill bit to drill out the first threads
If you have run bolt thread taps through the hole, then the first threads have the same diameter or larger than the threads in the rest of the hole. I did not see where you mentioned whether you were trying to thread the bolts in with the cylinder heads on of off. If they won't go in with the heads off, then the bolts have to be larger diameter than the tap.

If these are new bolts, then you might try threading the old bolts into the block to verify they thread correctly. If you have a local bolt supplier, take both the new and old bolts to them to check thread diameter. They may be mismachined or oversize bolts.
12-05-2009 07:35 AM
deadbodyman Aftermarket or chineese heads? you could try studs....I'm assuming you had them milled true....ME,I'd drill the hole(in the head) out bigger, cast is easy to drill out...It might even be a warped deck, EZ to check with a straight edge and a feeler gauge...Try switching the ones that work to the holes that dont ,that'll tell you if its the bolts or the holes.you could even try holding the head off the deck to clear the pins with a wooden dowel,get all the bolts started and remove the wooden dowel,but if the bolts are getting bound up that'll change the torque readings....I wouldnt mess with the block at all..
12-04-2009 06:52 PM
4 Jaw Chuck Measure the bolt, pitch in only one aspect of bolt sizing...sounds like you have a larger M13 or M14 bolt there.
12-04-2009 11:33 AM
oldred
Quote:
Originally Posted by heyjude076
Nix the drill. It could grab and suck itself in damaging too many threads.

You betcha! That thing would almost certainly grab and if it is a high torque drill it could damage the threads really deep, even a low torque drill would probably damage the first 3 or 4 threads.
12-04-2009 11:01 AM
cucumber1949
Quote:
Originally Posted by deadbodyman
Take the head off and the gaskit then thread the bolts in the holes...If they all work it must be the gaskit or the head's not lining up ...
That was my experience recently with a SBC. Removed head, cleaned up threads in engine block, and used new head bolts. One head bolt would not start properly with head sitting on the block and dowl pins engaged. Remove head and bolt would start and thread in perfectly into the block. Put head and gasket back on and no luck. I took the head over to the mill/drill and enlarged the problem hole by a 1/16" and problem solved.
12-04-2009 10:37 AM
heyjude076
Quote:
Originally Posted by hotbrat
m12 is pretty large. the dremel heads are tiny.

How about using a large drill bit to drill out the first threads
Nix the drill. It could grab and suck itself in damaging too many threads. Use the dremel or a round file and just go around the very top of the hole.
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