Gear Box Dowel Through Prop

Slidin Gator

Slidin Gator

Well-known member
I lost a cylinder on a geared LS3 (aluminum block). About an hour later on the run home I heard something go through the prop. On tear down I found that one of the gear/tranny alignment dowels was missing and the hole in the prop matches up well with a 1-ounce hunk of steel.

Noting that the setup was vibrating bad with a bad cylinder, my buddy poll is "never seen that before". The gear box is through drilled with no keeper cover, so this must not be a big issue??

Anyone ever seen this before? Aluminum block doesn't help for sure. I'm thinking of putting the dowels on the lathe and tapping them for a 5/16 or 3/8 screw to hold them in from the front side of the knock out holes.

IMG_3765.jpeg

IMG_3771.jpeg

IMG_3772.jpeg
 
Last edited:
SG that dowel would not even make the list of parts that would vibrate off of the engine in my book. You may need to play the lotto after that incident.

Have you found the cause of the lost cylinder?
 
every time i need to pull a dowel i have to find a 4000ton puller heat and cold with some magic to free one. unless the pin was loose to begin with ?????
 
kwanjangnihm said:
Have you found the cause of the lost cylinder?
Click to expand...
Not gonna jump to conclusions so no, She ate back to the ramp.. But that is another thread.

This thread is focused on the dowel and the way it hit the leading edge perfectly, sounded like a #1 metal wood teeing off!
 
kwanjangnihm said:
SG that dowel would not even make the list of parts that would vibrate off of the engine in my book.
Click to expand...
Me neither kwan, but I am a first time CM guy so I want to make sure I didn't do something stupid that no one mentioned. All my experience has been with car/truck transmissions where the dowel holes are blind on the transmission/gear so they can't come out.

Sooo, just to ask/answer the obvious question, "Why are Airboat gear box dowel holes through drilled vs. blind?"

I learned this part a while back starting with a locked-up engine. Car/truck torque converters/clutch include machine threads and a bare minimum of access where a racoon can get all the bolts out without rotating the crank. But the Airboat gear box kits include spacers, washers, nuts and bolts that require access to both sides. With the engine locked up, the through drilled gear box allows for pounding the dowels out so the gear box can rotate and all 6 drive-plate to flex-plate bolts can be removed.

Front Side of LS Dowel Hole.jpeg




The setup I have with the 8 Qt Camaro oil pan is worse. It's easiest to pull the oil pan to access the drive plate bolts/nuts.

Drive Plate Oil Pan Interference #1.JPG


Drive Plate Oil Pan Interference #2.JPG



I'm all friggin ears for a better way!
 
Hell yah, Friggin Chuck knows what I'm talking about.

[email protected] said:
You don't have to tear your engine apart. With the engine still bolted to the engine stand, take a hammer and punch and from the engine side, drive the 2 transmission alignment pins out the back of the gear case. Now pull the engine and gear box off the engine stand. Take the bolts out of the gear case and the gear box will rotate where you can get your flex to torque plate bolts out.
Thanks, Chuck
Click to expand...
 
Its funny that this post has came up. I am a first time carmotor owner after 30 years of aircraft boats. Less than 2 weeks ago I had my water thunder run hot and shut off. Couldn't see anything obvious, got pulled to the ramp. I had a hole in my radiator that looked like I had been shot with a 50 cal. After looking in the bottom of the boat, a hunk of steel was found, and one of my leading edges had a nick on it. I called Dave and he advised that maybe one a year come out. Just my luck!!! Bought motor, gear box, & prop over 3 years ago new, been saving up my nickels again, just got the boat completed November 21, 2025 and then this happens, not even 40 hours run time. I guess the dowel came out, hit the prop, shot into the radiator, and fell in the bottom of boat. Hopefully I will be able to get it to Dave this weekend for repairs.
 
Hello,
Been there...had a dowel come off the ox box....and damaged my prop and dent my radiator grille. Glad I had a radiator metal protection grille
EastBay
 
kwanjangnihm said:
Is there an assumption the dowel is working it's way rearward or can it work it's way forward and then fall out?
Click to expand...

Checking the cast iron 6.0 block I have on hand, the holes are stepped with a smaller ID keeping the dowel from going forward.

John Fenner said:
Sounds like a lateral drilling, threading and set screws is in order for the aluminum blocks.
Click to expand...
I agree John, A press fit in Aluminum is different than cast iron, Aluminum is "Squishy".

I know EastBay runs an aluminum block, I would be interested in C4 confirming his block material. It doesn't take long for steel pins in cast iron to corrode enough to seal the deal.

Set screws through the side of the block is one option. So far, I think the simplest yet idiot proof, reversible solution is to through drill the Dowels maybe 1/4" and run a 1/4-20 bolt all the way through with fender washer on the forward side bigger than the knockout hole. Regular inspection would be easy, just confirm the 1/4-20 is still tight.

Last option is adding cover plates on the gear box. Maybe this is a feature the box manufacturers could/should add.

The boat is decked over so the dowel went swimming, I was scratching my head for a while trying to figure out what the prop ate.
 
Last edited:
Sliden Gator it is an all aluminum block with the OX Box I have attached photos. I took and dropped it off Saturday with Dave and he was going to look it over this week. My concern is that it may have damaged the engine getting hot, since it punched a hole in the radiator. I will provide update when I receive one.
 

Attachments

  • IMG_7352.jpeg
    IMG_7352.jpeg
    179 KB · Views: 16
  • IMG_8013.jpeg
    IMG_8013.jpeg
    215.6 KB · Views: 16
Hello,
Aluminum block here. The dowels are not a solution. Better bolt up is the key, I think. I even had bolts backing out.
Keep threadlocker and bolts and torque wrench on my boat. LOL.
 
EastBay said:
Hello,
Aluminum block here. The dowels are not a solution. Better bolt up is the key, I think. I even had bolts backing out.
Keep threadlocker and bolts and torque wrench on my boat. LOL.
Click to expand...
Good input right there for sure. I have Helicoils installed on the bellhousing bolts, but I did use SST fasteners torqued to "That's good". The Helicoils allow the block threads to handle grade 8 capacity, so I will be going up on the torque spec on the bell housing bolts.

Blue thread locker always on everything I do. I'm also gonna make sure I don't send another 12 gauge slug through my prop, so I'm gonna "capture" them.

The prop damage report is $775 for two leading edge repairs and recoat all 3. $125 shipping each way, airBOAT.
 
You must log in or register to reply here.
Back
Top