Urgent: How can I stop bolts from continually coming loose

[Tank]

I have 4 bolts 3/8 UNC (into engine block Perkins) that despite Loctite and correct torqueing keep coming loose.
I am talking within 100klms. of being tightened.
I am going to drill and wire the (4 new bolts) heads together, but I don't think this is going to stop them losing their torque.
Anyone in the know (engineer mechanical) that could suggest maybe to tap a different pitch thread in the block (same dia. as now) and fit new bolts to suit, or any other way to stop this persistent problem, would be much obliged, Regards Frank.

[bee utey]

My guess is that the item that is held on by the 4 bolts is no longer flat to the block and flexing action is undoing the bolts. Thread pitch will have a marginal effect on the loosening of these bolts. Look carefully at the item and see if an extra brace can be added if you can't fix the mounting surface.

[Tank]

My guess is that the item that is held on by the 4 bolts is no longer flat to the block and flexing action is undoing the bolts. Thread pitch will have a marginal effect on the loosening of these bolts. Look carefully at the item and see if an extra brace can be added if you can't fix the mounting surface.
The item is the bracket that the twin cylinder Compressor sits on, this bracket is cast iron and is also the drain back for the compressor sump oil, I have had both mating (one to block other to comp. base) surfaces skimmed to true up, the block surface is perfectly flat and has the correct type gasket (paper, very thin) fitted.
The compressor that it holds up probably weighs 15k's and I was considering an extra brace to help support, but I was worried about harmonic vibes causing even more problems. Thanks for your advice, I may try replacing the cast iron bracket with a fabricated 1/2" steel bracket that would hold up the Harbour Bridge, Regards Frank.

[Blknight.aus]

which loctite are you using and do you want to be able to undo them?

you could replace the bolts with bolts that have the toothed underside that bite into the metal.

you can use a spring washer

if the bolts are going onto bare metal wihtout a washeryou can coat the underside of the head only with 680 or 690.

being cast iron what the minor and major diameter of the bolt holes?

are you trying to use 60 degree thread form (which will be undersized bolt) into a 55 degree thread form hole (which will be over size)

are you putting a flat washer under a spring washer?

are the bolts stretched?

if your mating with a gasket is the gasket compressing with use/exposure?

your probable best option for redrill and rethread is to go into a 2xd UNF helicoil if the compressor housing is going to limit the overall bold diameter.

in place of lockwire why not use loctabs or make a pair of small straps that you can use in lieu of loctabs and give the bolt heads a tack weld?

[Tank]

I used red loctite the first few times, also hardened flat washers and spring washers and very thin paper type gasket with adhesive sealer (liquid) on the block side and nothing on the bracket side, as per Perkins instructions, still came loose so used heavy type gasket with a very light smear of a special Sikaflex sealent recommended by a Perkins rebuilder.
There must be a vibration from the back of the injector pump shaft driven compressor, cannot feel it with your hand on the comp. at idle or revs.
I am contemplating studs with shanks with a slide/tight fit in the bracket holes (bracket holes are approx. 75mm deep and then fit anti-vibration serrated washers and lock nuts and some fold up tabs, would be near impossible to put a tack weld on 2 of the nuts as you can not even see them, much obliged for the advice, always helps to have some fresh ideas, anymore would be welcome, Regards Frank.

[BathurstTom]

Are you able to isolate the vibration of the compressor from the bracket? I would think that if it is a standard fitting, there is something other than the bolts/loctite etc causing the problem.

Tom.

[ramblingboy42]

Loctite gasket compound is also red and has no retaining qualities.

The colour doesn't determine it's characteristic.

Check that you are using correct Loctite......you can do it on internet search.....it's all listed.

[Busted Syncro]

G'day Tank,
Gee you have done all the right things and still have a problem.
I suggest that you may have a problem with your torque wrench. Has it been calibrated or tested? and can you get a lend of another one to try?.
It maybe under torquing the bolts. When you torque the bolts does it feel right?. Also remember Loctite has a max. temperature rating and can soften if it get to hot. You can get High temperature Loctite. Also what grade of bolts are they Grd5 or Grd8?.
Here is a link for a correct torque chart and note this is for nuts and not tapped holes.
Torque Chart (http://www.mpi-online.com/technical/torquechart.htm)
Here is another link for bolts into cast iron torques. Scroll down for Imperial data.
http://www.allpar.com/fix/body/fasteners.html
Good luck
Chris

[Tank]

I wish I had made a blue, but everything's kosha.
I'm going to get the local engineering shop to make me some studs with tight fitting (slide on) shanks to actually support the weight of the compressor.
Perkins should have fitted at least 2 dowel pins to locate and support this bracket, I believe that the bolts can not support the weight by clamping force alone, a couple of factory fitted dowel pins would have solved this problem from the start.
Again thanks all for your helpful advice, Regards Frank.

[Blknight.aus]

first things first...

if your not cleaning out the loctite or its getting oil contamination before it sets it wont lock,

if youre using spring washers and a flat washer you're doing it wrong for cast iron.

you dont need the machine shop to make custom hard to replace studs, there are bolts available via order with shank lengths in 1/16th inch intervals.

why not just taper drill the leading edge of the compressor housing and then use split collets to anchor it in?

you can also use large head bolts with the head drilled and tapped to take a 4mm bolt to act as a tensioner/brake bolt.

[Roverlord off road spares]

Not what you want to hear, ... But weld the suckers, then it'll be a problem of how to undo them in the future;)

[Rick1970]

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.

[JDNSW]

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

[ramblingboy42]

One more option is to go close tolerance bolts.

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

[Tank]

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.

[Blknight.aus]

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.)

[justinc]

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

[Busted Syncro]

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

[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.php?attachmentid=106995&stc=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.

[Tank]

Chris, JC and Dave, First and second time I used a Loctite product ($35 for the smallest bottle they could find can't recall the product # but it was for high vbration areas on jet aircraft) and the third time, each time the block threads were cleaned with a plug tap screwed in fully by hand (no metal removed), then Shellite, then a large bore rifle barrel wire and fibre brush's.
The bolts were similarly cleaned, then screwed in by hand and checked for play on the way in, then nipped up by hand, no play.
This bracket is a cast iron affair with a rectangular flange on the block side, it curves up to be the bottom sump plate of the compressor probably 8"x4" with multiple small bolts to seal and attach to the crankcase of the comp..
This bracket is hollow, as it is the drainback to the engine sump from the comp..
It is in a very awkward place and only 2 of the bolts are easily accessible, I had to buy a special tool to be able to torque one of the bolts, I am using a near new W&B torque wrench (one I had for over 30 years was pinched).
I have spoken to an engineer at Perkins and I suggested either Dowels, which would require the engine out as there is no room to drill dowel holes in block, said bolts with small clearance shanks would be as good.
There are many problems with supporting brackets, as they may make vibrations worse, I have a similar problem with the oil/water heat exchanger which has the 2 oil filters attached cracking the alloy housing, it would weigh at least 20ks. and it all hangs off 5 long and one short bolt.
As the engine is turbo'd it needs the extra oil cooling, thinking of fitting a remote oil cooler (aftermarket) with a dedicated fan, sick and tired of oil leaks.
I seem to remember years ago when I was fitting a Road Ranger box to a Perkins 6354 that perkins had a kit to fit 2 dowels the the flywheel housing, so it seems they didn't learn and put some dowels in these brackets that carry so much weight out and away from the block, will get some pics and let you know how it turns out, Thanks again, to all. Regards Frank.

[Tank]

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.php?attachmentid=106995&stc=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.
Pod, no it is definitely UNC, all of the bolts are SAE/AF, this Perkins T6354 seems to have been a Marine engine (built, not actually used as a boat engine), going by the Oil/Water heat exchanger and the fact that every other Perkins T6354 engine in a Truck doesn't even have the facility on the side of the block to bolt this bracket on to support and be the drain for the comp., neither have I seen this type oil cooler setup, Regards Frank.

[BathurstTom]

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.php?attachmentid=106995&stc=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

[justinc]

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

[Blknight.aus]

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

[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.

[Tank]

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.

[Tins]

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?

[Blknight.aus]

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?

[Tins]

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.

[Tins]

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



Not a bad idea. Haven't come across that before, but simple. If you can get the studs.

[Blknight.aus]

theres a few ways..

you just drill and hand broach the hex
you buy them online (or from specialist nut and bolteries)
you drill and tap and thread in a grub screw or a smaller bolt that you can get on with a spanner or socket.

you use a blind driving nut that has a smaller bolt in it wind the nut on, wind the small bolt in do the stud op using the nut, then when the stud is torqued hold the nut with the spanner and then undo the smaller bolt then wind the nut off.

if you have room you can just double nut it.

piece of cake.

desperate people just cut a grove thats 2mm deep with a hack saw and use an impact driver. clever desperate people wind it in with a normal screwdriver put the nut on just enough to stop the slit from splaying and then beat it with an impact driver.

[Tank]

Not a bad idea. Haven't come across that before, but simple. If you can get the studs.
Dave, spot on, I have some ARP studs with the allen head in the end of the stud scavenged from a motor that was never finished.
The studs will have to be fitted with everything in situ, major job removing the Heat Exchanger, if the studs I have are not suitable, have a friendly engineer with some nice machinery to make them up.
John if the studs were fitted first into the block there would be not enough room to get the bracket in place, piece of **** with the engine out.
The only hassle with the 2 bolts fitted this arvo was that the bolt shanks were about an 1/8" too long, so I had to grind and taper the shank and run a Die Nut up and extend the thread length accordingly, see what happens tomorrow, Regards frank.

[Busted Syncro]

G'day Frank,
Almost there!!!! Gee I thought working on my Leyland Mini Clubman was hard. Not anymore!!.
Chris

[Tank]

Bought 2x 3"x 7/16" inch bolts and cut them down and made studs, the top front one had to be 1/4" shorter and a heavy taper on the start of the thread just to be able to get it in to it's spot.
Couldn't get the block end of the thread to bottom out, so had to take it back out and shorten the Nut end of the stud an 1/8", then fit the Nyloc nut so one or two threads were through the nyloc part of the nut.
With the nyloc nut fitted to the shortened stud we could just get the block end of the stud started (heat exchanger was the culprit, in the way), so managed to bottom the stud in the block and wind on the nyloc nut a few more turns to reach the Torque value of F.T..
So finally got the bugger back on nice and tight, going on a run tomorrow so will see if it comes loose again, the last bolt (shortest) we just replaced with this much shortened stud only had about a 1/4" purchase in the thread in the block, so I would say Definitely not a Factory fitted item, thanks again for all the great advice, much obliged, Regards Frank.

[justinc]

Dave, spot on, I have some ARP studs with the allen head in the end of the stud scavenged from a motor that was never finished.
The studs will have to be fitted with everything in situ, major job removing the Heat Exchanger, if the studs I have are not suitable, have a friendly engineer with some nice machinery to make them up.
John if the studs were fitted first into the block there would be not enough room to get the bracket in place, piece of **** with the engine out.
The only hassle with the 2 bolts fitted this arvo was that the bolt shanks were about an 1/8" too long, so I had to grind and taper the shank and run a Die Nut up and extend the thread length accordingly, see what happens tomorrow, Regards frank.


That Dave... not just a pretty face... ☺

[Dare2]

Just a thought make sure you the loctite primer this may help alse have you tried shake proof internal star washers.
Rocky

Sent from my SM-G920I using AULRO mobile app

[Blknight.aus]

That Dave... not even a pretty face... ☺

Fixed it for you...

its configured for radio work.

its kinda like the dentist "we cant show you his face" tooth paste add but its got nothing to do with the privacy for me, its just that most people dont spend their time under their vehicles trying to look up past the engine Im spannering on.

[justinc]

Fixed it for you...

its configured for radio work.

its kinda like the dentist "we cant show you his face" tooth paste add but its got nothing to do with the privacy for me, its just that most people dont spend their time under their vehicles trying to look up past the engine Im spannering on.

Ha ha yes i appeared briefly on the first Seriously Series Heading West vid and on camera i am much more awkward than i am already in real life 😮😮😮😕😣😣 at least my county made a half decent backdrop ☺

Jc