Thread: Urgent: How can I stop bolts from continually coming loose

Originally Posted by POD

Frank it was mentioned earlier but this diagram might better explain, being a Perkins might the threads in the block be whitworth form?

http://www.aulro.com/afvb/attachment...1&d=1458164300

If not, then I think you are on the right track with dowelling it.
However, from your description, it sounds like a stock installation (?) so it doesn't make sense that modification is necessary to make it stay there.

Yes, that was my thinking - that is was a stock install and accordingly I suggested looking for an alternate cause rather than fixing the installation itself. But looking at Frank's later post, it likely isn't a standard install.

Tom

How are the actual engine mountings? If yhe engine has poor vibration dampening like solid frame to block mounting or collapsed rubber insulators then a 'reflective' vibration will be present in and through the engine. It may be Worth investigation considering that you have also had other problems with block mounted accessories?

Jc

I know that product, its a sealant not a locking agent (although it works well as one on AC spec tight tolerance bolts. Its as useful as vaseline as a locking agent on normal auto clearance bolts.

if you werent making metal when you ran your tap that may be half a hint to your problem the female thread is worked oversize.

you need a high clearance locktite like umm 292 or a high temp bearing mounting goop such as 680. you can also increase the locking quality by using the accelerant/primer/cleaner which from memory is 4741. shellite (and most other standard cleaners is a slovent to most loctites and delays the curing process.

best of luck with it

On some earth moving gear we have used tubes on the bolts to increase the length of the bolt. Dont know your particular application if it will fit. This extra stretch seems to absorb the vibrations better with a lick of locktite. In worst case as a butcher i have used devcon on studs on a loose hole.

Originally Posted by manofaus

On some earth moving gear we have used tubes on the bolts to increase the length of the bolt. Dont know your particular application if it will fit. This extra stretch seems to absorb the vibrations better with a lick of locktite. In worst case as a butcher i have used devcon on studs on a loose hole.

Thank you all, seems I have been giving you the wrong info.
I confused the water/oil heat exchanger bolts with the compressor drain back mount and bracket.
Got the bolts out today, they are 7/16 NF, not 3/8 UNC as I previously stated.
These 7/16 bolts have about 1 1/4" thread in the block and about 3/8" comp. bracket flange to get through, with the washers there is 1 3/4 bolt length from under head bolt to end of bolt.
Problem is that they are threaded right to the bolt head, no shank, the old bolts had been polished and removed most of the thread where the comp. bracket sat on the threads.
Bought some new 7/16 NF bolts with a 1/2 of shank under the bolt head, which are a nice fit in the bracket holes.
Now I can only get 2 of these new bolts in because of the cursed heat exchanger being in the way, so tomorrow I'll get 2 studs made up with an inch thread on the block end, a 1/2" shank to fit through the bracket and washers and a 1/2 thread for the locknut.
May have to trim to get in but as I don't have a bolt head to wangle in there it should do the job, will keep you all posted, Regards Frank.

Originally Posted by Tank

Thank you all, seems I have been giving you the wrong info.
I confused the water/oil heat exchanger bolts with the compressor drain back mount and bracket.
Got the bolts out today, they are 7/16 NF, not 3/8 UNC as I previously stated.
These 7/16 bolts have about 1 1/4" thread in the block and about 3/8" comp. bracket flange to get through, with the washers there is 1 3/4 bolt length from under head bolt to end of bolt.
Problem is that they are threaded right to the bolt head, no shank, the old bolts had been polished and removed most of the thread where the comp. bracket sat on the threads.
Bought some new 7/16 NF bolts with a 1/2 of shank under the bolt head, which are a nice fit in the bracket holes.
Now I can only get 2 of these new bolts in because of the cursed heat exchanger being in the way, so tomorrow I'll get 2 studs made up with an inch thread on the block end, a 1/2" shank to fit through the bracket and washers and a 1/2 thread for the locknut.
May have to trim to get in but as I don't have a bolt head to wangle in there it should do the job, will keep you all posted, Regards Frank.

Hope you get it sorted Frank. Is there sufficient manoeuvring room to get the thing over the studs you plan to fit?

my money is on he'll get the studs bossed with a hex use an alen key to wind them in and then wind the nut on or he'll over wind the nut, position everything and then wind the stud through the nut into the housing before tightening the nut down.

not surprised it worked loose if the threads made it all the way to the underside of the head I'll bet the head stretched loose at about the last 2 turns of thread.

any percentage on using a specialist off the shelf short shank bolt that'll do some support work with a spacing tube to make sure the bolts fill the hole?

Originally Posted by Blknight.aus

not surprised it worked loose if the threads made it all the way to the underside of the head I'll bet the head stretched loose at about the last 2 turns of thread.

Agreed. I'll bet they weren't original fitment.