Help: Engine mount bolt holes...

[idleup]

I was drilling the holes to 3/8" for the engine bolts and noticed that the gusset (F-601C) in between the firewall and the WD-602 Upper engine mount bracket cracked in a couple of places. You can only tell looking in the hole since it is sandwiched between two steel plates. I then proceeded to do the other hole with a step drill being very careful and it happened again... is this a common thing? is it a problem? After a little investigation I found that piece is aluminum (.125) and is primarily a spacer between the engine mount bracket and the firewall so I am not sure if it is a problem... any help would be appreciated.

[Finley Atherton]

Matt,
My memory of this area is a bit hazy but I recall the bolt hole goes through the area where the gusset and the angle stiffener butt against each other. Maybe the ?cracks? you are seeing is the join line between these two parts??

Fin
9A

[Guy Prevost]

That would be my guess. I drilled mine yesterday and noticed that the hole went right through a joint in the first layer of aluminum aft of the firewall. The steel and stainless steel layers are whole, of course.

Guy

[idleup]

Originally Posted by Guy Prevost

That would be my guess. I drilled mine yesterday and noticed that the hole went right through a joint in the first layer of aluminum aft of the firewall. The steel and stainless steel layers are whole, of course.

Guy

Yes, on mine the steel layers sandwiching the aluminum gusset is also find. It is the aluminum gusset that cracked. I can tell they are cracks because they run longitudally, I can see the layers between the metals that I am drilling and it is not those cracks. I thought maybe it was from having a dull bit or something but it still happened on the other side when I used a step drill. The gusset, since it is sandwiched between two steel plates, is not visable and since this fuse was a quickbuild I never built that part.

- Matt

[Finley Atherton]

Matt,
I am confident the cracks you see are not cracks. Perhaps I did not explain it clearly. The gusset and the flat part of the stiffener are butted against each other and not layered on top of each other. When you drill through this butt join you WILL see what appears to be two cracks running in the same direction as the hole. I see yours is a QB so you may not be familiar with how this part is put together. I suggest you have a good look at the plans and you will see that the hole is drilled right through the area where the two parts are butted against each other. If you do indeed have cracks you will see extra cracks than the two caused by the butt join. Hope this helps

Fin
9A (slow build)

[idleup]

Originally Posted by Finley Atherton

Matt,
I am confident the cracks you see are not cracks. Perhaps I did not explain it clearly. The gusset and the flat part of the stiffener are butted against each other and not layered on top of each other. When you drill through this butt join you WILL see what appears to be two cracks running in the same direction as the hole. I see yours is a QB so you may not be familiar with how this part is put together. I suggest you have a good look at the plans and you will see that the hole is drilled right through the area where the two parts are butted against each other. If you do indeed have cracks you will see extra cracks than the two caused by the butt join. Hope this helps

Fin
9A (slow build)

Ah... I understand what you are saying now and you may be correct. I guess even if the gusset was cracked this would confirm that it wouldnt matter as the gusset must not be that critical to the strength of the assembly if you are drilling a hole right through the area it butts up to another part...


- Matt