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

There are some special segrated washers available that I have seen on a few different things that have a habit of coming loose .Konnect / Coventry Fastners have them from memory.

Frank, are the bolts stretching? if this is the case, what you need is harder bolts. Marking the heads so you can tell if they turn may help you to be sure whether they are stretching. If they loosen by initially stretching and then turning, retightening them will see them tighten past the previous marks.

John

One more option is to go close tolerance bolts.

Looks like you've had plenty of suggestions tank, something must work.

Thanks once again for some very good tips/advice.
I am convinced that due to the weight of the compressor, which is at least 15kgs. and it is driven by a rubber coupling shaft from the back of the injector pump that the clamping force of the 4 bolts is not enough to support the weight, I believe that 2 solid dowel pins to locate the bracket and support the weight would allow the bolts to clamp and hold tight.
I think if I fit 4 close fit studs with the shanks supporting the weight the 4 nuts will have a chance at staying tight, I will give it a go tomorrow and report back the results after the next trip north, John (JDNSW), the bolts that came loose were new grade 8 bolts which I measured with a micrometer before installing, they are still the same length, the threads in the block seem to be good the new bolts were fitted without the bracket, hand tight then lightly nipped, no play or movement, the shanks on the old bolts were smaller dia. than the thread as are the last new bolts fitted, will try to get new bolts with thicker shanks as I believe that the shanks will support the weight, like a couple of dowels would, Regards frank.

4x 3/8th bolts should be able to support in the order of tens to hundreds of thousands of pounds of load.

if you're checking thread condition by seating the bolts and then tighteneing them and then checking for free play you're not effectively checking the condition of the threads in the block. I suspect that the root cause of your issue is the bolts and the way you are putting them in.

try this.

Use a high temp loctite, 292 or one of the bearing mounting locktites. Pre heat the block and the bolts, get the block to about 60 degrees and the bolts to around 80 degrees. Use grade 10 bolts (just confirm that your grade 8 unfs had the 6 radiating lines in line with the Apexs of the head flats and not the center of the flats.)

I think that studs and locknuts with locating dowels should be all that is required Frank. Go up to7/16" UNC if possible or even 1/2"UNC. Can you post a pic of the assembly bolted up?

JC

G'day Tank,
Hang in there and we all are waiting for the final solution.
Just a thought. Are the bolts bottoming out in the holes and the bolts are to long?. When you torque them up they maybe bottoming out slightly before it can pull down the plate to the correct torque.
Chris

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.