Hello I have a 2001 classic airboat 16x8 350dd I recently purchased. The first time I had it out I noticed the oil pressure was only around 16psi at 3,000rpms. When I got it home I grabbed the propeller hub and you can move the crank about 3/16’s of a inch. At this point I’m pretty sure this is why the oil pressure is low as well. Also there is oil all over the propeller. I started to pull the engine out of the boat to either have it rebuilt or find another 350 for it. This is my first 350dd airboat so I was looking for some input on what I should do from here. The boat is spinning a whirlwind stump puller. The one time I had it out it would cruise at 35mph, 3000rpms, and propeller set at full pitch. What do you think would be best to do from. Replace the crank bearings and run it, do a complete rebuild, or find another 350 used and put in it? How much horse power do I need for this set up? I’m new to this so thanks for the help everyone.
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350 direct drive worn crank bearings
- Thread starter damonjy19
- Start date
SWAMPHUNTER45
Well-known member
How do you plan to use it?
A 16ft hull with any direct drive is going to be limiting.
A 16ft hull with any direct drive is going to be limiting.
SWAMPHUNTER45
Well-known member
Your best value for the dollar will be a 383 with a low duration cam. I'm sure you can find a good builder up there to help you.
Stroke is your friend with direct drive.
Your engine is going to live in the 1,800 to 3,100 rpm range depending on your prop so the new engine needs to be built for that purpose.
RV type cam, truck intake and heads, smaller carb, long tube headers.
Stroke is your friend with direct drive.
Your engine is going to live in the 1,800 to 3,100 rpm range depending on your prop so the new engine needs to be built for that purpose.
RV type cam, truck intake and heads, smaller carb, long tube headers.
Slidin Gator
Well-known member
If you are happy with how she runs, then no, get a junkyard Vortec 350 and go. Otherwise upgrade, just remember any motor upgrades will include prop/hub upgrades, since your present prop is maxed out.damonjy19 said:
SWAMPHUNTER45
Well-known member
Yea something has me puzzled ?
A 350 would not be spinning a Stump Puller MAXED OUT I don't think would it Chuck?
That prop was wither a 72 or 78 when made and designed to be enough to hold a 540 or big block car motors output.
A worn out 350 may make 300 pounds torque at best I just can't see that prop being maxed out.
Below is a copy of a post made by Patti years back:
Just a quick note on the older Stump Puller blade series. This blade style is known as a workhorse, so there are still many of these blades around, and we can still make new ones on request.
The Stump Puller series came in both a standard 72" (max RPM 3000) and a 78" (max propeller RPM 2700).
*The direct replacement for the Stump Puller 72" is the Whisper Tip 72" and the direct replacement for the Stump Puller 78" is the Whisper Tip 2.0 78".
The Stump Puller 72" is a wide-blade, and as a 2-blade is often best matched to an a/c 520 or 540, or a big-block direct-drive auto engine. Though I have seen them on smaller 4-cyl a/c and 220 GPUs, just with a lower blade angle. For a direct drive set-up, the most important factor is setting the blade angle to get as close to 3000 RPM WOT (or a little lower on a/c motors) without going over.
So to answer your question, as others have said, the pitch you need to set the Stump Puller 72" is the one that holds your motor at your target WOT RPM, without letting it go over 3000 RPM. For a static set-up, you want to undershoot by about 200 RPM for your WOT on the water RPM target. If you line up the seem line of the blade with the numbers on the hub, this will give you a starting point. Do a run-up and see what RPM you get, then stop and adjust the angle up or down. Each degree of pitch change makes about 100 to 200 RPM of change on the engine. It's a pretty fine resolution. You can usually dial it in perfect in 2 to 3 runs.
Sincerely,
Patti
A 350 would not be spinning a Stump Puller MAXED OUT I don't think would it Chuck?
That prop was wither a 72 or 78 when made and designed to be enough to hold a 540 or big block car motors output.
A worn out 350 may make 300 pounds torque at best I just can't see that prop being maxed out.
Below is a copy of a post made by Patti years back:
Just a quick note on the older Stump Puller blade series. This blade style is known as a workhorse, so there are still many of these blades around, and we can still make new ones on request.
The Stump Puller series came in both a standard 72" (max RPM 3000) and a 78" (max propeller RPM 2700).
*The direct replacement for the Stump Puller 72" is the Whisper Tip 72" and the direct replacement for the Stump Puller 78" is the Whisper Tip 2.0 78".
The Stump Puller 72" is a wide-blade, and as a 2-blade is often best matched to an a/c 520 or 540, or a big-block direct-drive auto engine. Though I have seen them on smaller 4-cyl a/c and 220 GPUs, just with a lower blade angle. For a direct drive set-up, the most important factor is setting the blade angle to get as close to 3000 RPM WOT (or a little lower on a/c motors) without going over.
So to answer your question, as others have said, the pitch you need to set the Stump Puller 72" is the one that holds your motor at your target WOT RPM, without letting it go over 3000 RPM. For a static set-up, you want to undershoot by about 200 RPM for your WOT on the water RPM target. If you line up the seem line of the blade with the numbers on the hub, this will give you a starting point. Do a run-up and see what RPM you get, then stop and adjust the angle up or down. Each degree of pitch change makes about 100 to 200 RPM of change on the engine. It's a pretty fine resolution. You can usually dial it in perfect in 2 to 3 runs.
Sincerely,
Patti
Dying_breed
Well-known member
What did you end up with? Im in the same boat figuratively great running wore out 350dd. Gotta litte jingle in my pocket but idk if im gonna rebuild it for my cheapest option... Or have it bored and go with a summit 383 stroke kit. Or keep stalkin the web for a good 400 or 383 short block and beat the machine shop labor. Too many options and so little paitence.. I just wanna slide lol
flcracker9
Well-known member
Been there, done that. I bought a DD boat for my Son a few years ago. It is a 12' Big O hull with poly, and came with a Vortec 350ci and a 70" Q series prop. It ran well, even ran dry pretty good with 2 men on board. It finally took a dump on us one day (slung a rod out the side of the block), so we were faced with finding an engine. I ended up with a used 1 piece rear seal block, took it to .040 over, installed a Scat stroker crank (making it 385") with flat top pistons, but stayed with the Vortec heads and Vortec roller cam to keep the torque curve in the lower RPMs. We completed the build about 2 years ago, and I don't know if you can do any better as far as a DD boat. It jumps up on plane much quicker than the stock 350, and he pretty much follows us wherever we go. We run the Kissimmee chain quite a bit, not sure if you're familiar with that area, but he can run up the ridge with 2 men, and run up in the cabbage palms at the Glory Hole pavilion with no issues getting back to the water. You are correct about thrust bearing wear though, we've been keeping an eye on it, knowing we will need to replace the thrust bearing at some point, no way around that with a DD. I'm lucky enough to be able to do most of this work at home, the only thing I had to farm out was prepping the block and balancing the rotating assembly, which helps reduce maintenance costs. Just my personal experience.
SWAMPHUNTER45
Well-known member
FLCRACKER9 what are you running for oil in the DD engine ?
flcracker9
Well-known member
SWAMPHUNTER45 said:
Swamp, if my memory serves me correctly, when I assembled the engine (I'm no professional by any stretch), our main bearing clearances were a little on the tight side (as measured with a bore gauge and micrometer, double checked using plasti-gauge), so I went with a 5W-20 oil (conventional oil). I believe My Son has since switched to 5W-30 synthetic.
SWAMPHUNTER45
Well-known member
The one thing I can tell you is that the amount of pressure the prop puts on the thrust is extreme. The more wear you get to the bearing the less a piss thin oil can do to cushion. Not sure if you have heard me talk of the "Branch Brew" but his DD engines last for years.
15w-40 Shell Rotella T 4 Qt
Lucas oil stabilizer 1 Qt
CompCam#159 Break in additive 4-6 ounces
What bearings did you use?
15w-40 Shell Rotella T 4 Qt
Lucas oil stabilizer 1 Qt
CompCam#159 Break in additive 4-6 ounces
What bearings did you use?
flcracker9
Well-known member
SWAMPHUNTER45 said:
King XP Bearings, mains and rods. We are going on 3 years now, but it doesn't get used a whole lot. My best guess is maybe 80 - 100 hours. We went with a thin oil based on bearing clearances for the initial break-in, and changed the oil after 10 hours. Crankshaft end play is good right now, but we may take your advice and use the combo above, damn sure can't hurt :thumbleft:
SWAMPHUNTER45
Well-known member
Good choice on the bearings
We use the big block Chevy bearings in our stroked engines, I have used XPs before.
We use the big block Chevy bearings in our stroked engines, I have used XPs before.