Engine mount question

[mfryer]

I acquired a used engine mount for my EZ project. I noticed numerous tiny screws all over the mount. Can anyone enlighten me as to there purpose?

 

Also, I am considering having the mount bead blasted and powder coated. I anyone knows of any reason not to do that please let me know. Thanks

 

[schmeddz]

The screws are where you put in the linseed oil so the interior of the tube doesn't rust from the inside out. Inject it with a syringe. Blast away and use a good epoxy primer. Degrease thoroughly after playing with the linseed oil however. Or wait until it's painted to play with the oil. Have fun.

[Cozy Girrrl]

The holes that are plugged with screws make it a lot easier to weld the mount. As you weld the tubes heat up and cause the air inside them to expand and would otherwise blow holes through welds as you try to complete them.

 

If you oil the mount internally it will make repairs difficult. If you powder coat it, it is possible for it to crack under the powder coat and hide the damage, also the powder coat would have to be completely removed from the areas surrounding any attempt to repair a cracked tube or broken weld.

 

We usually suggest that people lightly prime the mount with chromate or oxide primer then coat lightly with "refridgerator white" gloss paint.

 

Regards, Chrissi

[schmeddz]

Yeh Yeh, What she said is better than what I said! I missed the fact that he wanted to powdercoat. I've only done three mount refurbs. The Gurls do multiple builds. The linseed oil leaking down my white (painted) mount did clue me in that it was cracked on my first Long-Ez.

[mfryer]

Thanks for the insights. I am very glad I asked before I jumped the gun on powder coating. I presume the bead blasting is ok?

 

Chrissi, can you provide more information on the recommended primer and paint, for instance what brand would you recommend?

[Lynn Erickson]

I acquired a used engine mount for my EZ project. I noticed numerous tiny screws all over the mount. Can anyone enlighten me as to there purpose?

 

Also, I am considering having the mount bead blasted and powder coated. I anyone knows of any reason not to do that please let me know. Thanks

 

[ATTACH]1653[/ATTACH]

The screws are there to try and keep the linseed oil inside the mount tubing but is not a good way to do it. the screws have been the cause of cracks starting at the holes due to stress risers made by the thread cutting action of the screws. the tubes should have the linseed oil put in and then the holes are welded up. a properly made mount should come from the builder with this procedure already done. if the mount is made with this procedure a light bead blast and powder coat is OK. if the mount was to crack the linseed oil will leak out and expose the crack better then any visual inspection will no matter what type of corrosion coating is used. repair to a cracked mount can be performed on a mount with linseed inside the tubes by re-drilling the holes and flushing the inside of the tube with a solvent and drying before welding. but before the cracked tube is repaired by welding there needs to be a complete inspection of the tube to determine the internal condition and wall thickness. many times it is better to replace the tube then repair it. simply welding up the crack is not acceptable and can be dangerous. I have been seeing more and more of the Brock long and vari eze mounts that have cracked. many of them did not get the proper corrosion treatment inside the tubes and the ones with screws are cracking at the screw holes.

[Cozy Girrrl]

For what it is worth we do a good busines in "replacement" engine mounts, whether they were made by Brocks, Weldtech or otherwise. Drilled, undrilled, oiled or not. They all typically crack within 3/4" of the welds in the heat affected zone or the welds themselves crack. Some crack at the vent/oil holes. The Long-ezs are so highly cantilevered it does not surprise me they crack. Painting with a thin coat bright white paint and inspecting frequently is your best guard against failures from a cracking engine mount, powder coat is mighty pretty but may delay early detection.

 

Drilling vent holes was a required thing with other welding techniques but with TIG is not entirely necessary. You leave a small gap in the weld to vent the tube and when the mount is finished you go back and close your gaps. On a cooled structure you are in and out of a TIG weld before there is any internal pressure to blow out a weld.

 

Your best preventive action for engine mount failures is probably having an experienced technician do a dynamic balance on your engine/prop/spinner while hooked up to a laptop. All the rest of the remedies are not going to help you if you have vibration induced stresses on your engine mount.

 

Regards, Chrissi

[michaelj]

As an alternative to drive screws or welding the vent holes up I recall that flox works pretty well. It would be easy to drill out the flox years later if you needed to drain out the oil for a repair.

[mfryer]

It seems that my question has opened up a can of worms. Let me analyze the responses....

 

• Powder coating is not recommended due to its possible concealment of stress cracks. Rather a more conventional white paint over a corrosion resistant primer is recommended.

• The holes are either for injection of linseed oil for corrosion protection and as a side benefit will assist in detection of stress cracks, or for releasing hot gasses during manufacture.

What I would like to know at this point is...

 

• Is my mount is safe?
• What sorts of inspection should I perform to ensure the mount is safe?
• What should I do with the holes? (should they be welded over? floxed? left alone with the screws in place?)

Unless someone has a good reason for me to alter my plan I will have the mount bead blasted, inspected for cracks, primered and painted white (while I would like the mount to be pretty, function trumps pretty). I will leave the holes as is and use the existing screws.

 

Thanks for all of your inputs.

[Lynn Erickson]

It seems that my question has opened up a can of worms. Let me analyze the responses....

 

• Powder coating is not recommended due to its possible concealment of stress cracks. Rather a more conventional white paint over a corrosion resistant primer is recommended.

• The holes are either for injection of linseed oil for corrosion protection and as a side benefit will assist in detection of stress cracks, or for releasing hot gasses during manufacture.

What I would like to know at this point is...

 

• Is my mount is safe?
• What sorts of inspection should I perform to ensure the mount is safe?
• What should I do with the holes? (should they be welded over? floxed? left alone with the screws in place?)

Unless someone has a good reason for me to alter my plan I will have the mount bead blasted, inspected for cracks, primered and painted white (while I would like the mount to be pretty, function trumps pretty). I will leave the holes as is and use the existing screws.

 

Thanks for all of your inputs.

safety is the highest concern here, first where did the mount come from, was it used on a flying airplane or just stored for many years. if on a flying airplane , how many hours? you have a mount that was welded up with holes to releave pressure build up during welding and then they are used to inject a corrosion preventative oil. I have seen mounts welded using other methods but this is the FAA approve method. mounts that are welded up not using this method may work but for how long. how long will it be before the tube corrode from the inside out and ruin some ones day. if it has screws in the holes, why are the screws there? is there linseed oil in the tubes, if so then leave them there it is an acceptable way to plug the holes ,not the best way but it does work. oil in the tubes does help in the life span of the mount and if there is no corrosion inside the tube then there will not be a stress crack that is started by corrosion. the same applies to the outside of the tubes , some type of coating is needed to prevent corrosion. solvent based paint or non solvent based paint both do the job and either one will try to hide a crack but in every case I have found a crack it showed up with a crack in the paint. the best at hiding the crack is the new type aircraft paint. as it has a very high surface strength and stretches a lot before it cracks. paint like epoxy or power paint are brittle and will show cracks from bending or stress even before there is a crack.

[Cozy Girrrl]

...some type of coating is needed to prevent corrosion. solvent based paint or non solvent based paint both do the job and either one will try to hide a crack but in every case I have found a crack it showed up with a crack in the paint. the best at hiding the crack is the new type aircraft paint. as it has a very high surface strength and stretches a lot before it cracks. paint like epoxy or power paint are brittle and will show cracks from bending or stress even before there is a crack.

Lynn, we strongly dissagree about powder coat paint and advise against it to all of our engine mount customers.

Powder coat looks great, it is thick and flows out beautifully when it is baked. Unfortunately it does not adhere as well as solvent or epoxy based paints.

 

"in every case I have found a crack it showed up with a crack in the paint."

 

This is exactly the problem with powder coat. You will not see the crack forming under the powder coat until it is large enough to cause a break or separation in the paint or the tube finally fractures through. With powder coat you may not see the crack coming until it is larger. Why take the chance?

Regards, Chrissi

[Lynn Erickson]

Lynn, we strongly dissagree about powder coat paint and advise against it to all of our engine mount customers.

Powder coat looks great, it is thick and flows out beautifully when it is baked. Unfortunately it does not adhere as well as solvent or epoxy based paints.

 

"in every case I have found a crack it showed up with a crack in the paint."

 

This is exactly the problem with powder coat. You will not see the crack forming under the powder coat until it is large enough to cause a break or separation in the paint or the tube finally fractures through. With powder coat you may not see the crack coming until it is larger. Why take the chance?

Regards, Chrissi

In my 35 years of building and repairing aircraft engine mounts the only crack that I found that did not show up in the surface coating was one that had been painted with aircraft poly urethane solvent based paint. I believe this is one of those old wives tales that says power coating sticks so good it won't shows cracks, I believe it is the opposite, as you have stated the stuff does not adhere as well solvent based paint and this is why it will crack or flake off at a point of stress and show a crack or bend even before some other coatings. 35 years ago this was a topic of discussion in A&P school with the instructor who also had little or no experience with the stuff on engines mounts to back up his statement. back then we may have been taking a chance by using the stuff. thats why the call it experimental aircraft . but after using it successfully for all these years I believe this experiment is over and is a success.

[Cozy Girrrl]

Our experience differs so we'll just disagree.

[dirtdox]

 

Drilling vent holes was a required thing with other welding techniques but with TIG is not entirely necessary. You leave a small gap in the weld to vent the tube and when the mount is finished you go back and close your gaps. On a cooled structure you are in and out of a TIG weld before there is any internal pressure to blow out a weld.

 

 

Venting can also be accomplished by drilling a hole at the tubing intersection before welding the notched tube in place. The notched tube covers the hole. This way the whole structure gets vented and no holes need plugged.

[mfryer]

safety is the highest concern here, first where did the mount come from, was it used on a flying airplane or just stored for many years. if on a flying airplane , how many hours? you have a mount that was welded up with holes to releave pressure build up during welding and then they are used to inject a corrosion preventative oil. I have seen mounts welded using other methods but this is the FAA approve method. mounts that are welded up not using this method may work but for how long. how long will it be before the tube corrode from the inside out and ruin some ones day. if it has screws in the holes, why are the screws there? is there linseed oil in the tubes, if so then leave them there it is an acceptable way to plug the holes ,not the best way but it does work. oil in the tubes does help in the life span of the mount and if there is no corrosion inside the tube then there will not be a stress crack that is started by corrosion. the same applies to the outside of the tubes , some type of coating is needed to prevent corrosion. solvent based paint or non solvent based paint both do the job and either one will try to hide a crack but in every case I have found a crack it showed up with a crack in the paint. the best at hiding the crack is the new type aircraft paint. as it has a very high surface strength and stretches a lot before it cracks. paint like epoxy or power paint are brittle and will show cracks from bending or stress even before there is a crack.

Of course safety is of paramount (no pun intended) importance, this is why I am asking these questions and I truly appreciate the input of everyone here who takes the time to read and discuss these topics.

 

I do not have a history of the mount. I will attempt to get that info, but I doubt I will glean much information from its source. However, I can say the the mount defiantly is used, it was delivered to me with oil and dirt lightly coating its exterior and included some tubing clamps and wire ties that I have removed. I see no signs of cracks or stresses. I got a very good deal on the mount and I intend to use it unless I have any indication it is unsafe.

 

I have decided to follow Crissi's advise as to its finish. I appreciate your arguments, however no one has pointed out a significant benefit to power coating and when considering the caveat that the mount might need to be repared or replaced I do not see the justification for the additional expense and perhaps risk it might conceal a crack.

 

To put it another way.... Perhaps there is no risk to powder coating, however there is also no or little risk to a more conventional paint and it will save me some money.

 

I will leave the screw in. However is it your opinion that the mount should be filled with oil, or merely coating the interior?

[Lynn Erickson]

 

To put it another way.... Perhaps there is no risk to powder coating, however there is also no or little risk to a more conventional paint and it will save me some money.

 

I will leave the screw in. However is it your opinion that the mount should be filled with oil, or merely coating the interior?

you will realize one of the advantages of power coating by the time you have finished the engine install and the mount looks like it needs a new paint job due to all the assembly related scrapes and scratches.

the amount of oil is only about 1/2 CC per tube just enough to coat the inside. linsead oil is one type used because it will creep over the surface and coat the inside evenly

[mfryer]

you will realize one of the advantages of power coating by the time you have finished the engine install and the mount looks like it needs a new paint job due to all the assembly related scrapes and scratches.

the amount of oil is only about 1/2 CC per tube just enough to coat the inside. linsead oil is one type used because it will creep over the surface and coat the inside evenly

The engine mount is off to be beadblasted. I will keep the powder coat option in mind, however I have been hearing from others (machinist that I know) that powder coating might not be a good idea. Perhaps if someone could point me in the direction of some literature or an FAA AC it might help me to educate myself.

 

After finishing (or sooner if I do not get to that soon). I will add more oil to the inside to ensure it has a fresh coating to limit corrosion. Thanks.