RX7 drive unit question

Automotive powered airboat discussion.
akruffrider
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RX7 drive unit question

Postby akruffrider » Wed Jul 09, 2014 5:44 pm

Hi guys, just getting into airboats. I've driven a couple of small ones over the last few years and been running jet boats for many years. Any way i picked up a 1986 mazda RX7 engine with a 2 to 1 belt drive unit. I'm having trouble getting the lower pulley off of the motor. In the middle of the pulley is a hole that is about an inch deep and has some messed up threads. Inside it looks like it might have been drilled. I'm trying to figure out if it just needs pressed off, someone broke a bolt off, or if it comes off some other way. I have searched all over and don't know who made this reduction unit as it has no markings on it, the plate that attaches to the prop says panther airboats but i'm not sure if that is part of the reduction unit. Thanks for the help ahead of time this thing is making me crazy :banghead: !!

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gyrocopter582
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Re: RX7 drive unit question

Postby gyrocopter582 » Wed Jul 09, 2014 7:53 pm

Judging by the length of the pulley, and the roller bearing inside the pulley, there must be
a support pilot bearing that helps carry the side load on the pulley.
There appears to be a snap ring retaining the plug with the stripped hole.
Is that a snap ring? I would suspect there is mounting bolts, or a large gland nut behind the plug.
"Amaze your friends, annoy your neighbors"

akruffrider
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Re: RX7 drive unit question

Postby akruffrider » Wed Jul 09, 2014 8:36 pm

Thanks for the reply. I though there might be a snap ring too. What looks like a snap ring is a small groove worn in by the the inner part of the bearing which is not shown in the picture. Anybody think that if i removed the bearing there might a few bolts around the perimeter of the drive pulley?? Don't want to mess up the bearing pulling it out (its press fit) if that won't help me get the think off!

akruffrider
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Re: RX7 drive unit question

Postby akruffrider » Wed Jul 09, 2014 11:18 pm

whew :cheers: figured it out! Thanks everyone for looking. And gyrocopter you where right that it was a plug. I decided to re thread the hole and screwed in a slide hammer. Slide hammered out the plug and the bearing and there were 6 bolts to take off the pulley!! :D

needcoffee
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Re: RX7 drive unit question

Postby needcoffee » Thu Jul 10, 2014 5:21 am

You have a Northwest Aero PSRU. I had the same question a few years back.

http://www.homebuiltairplanes.com/forums/general-auto-conversion-discussion/10762-northwest-aero-psru.html

This manual isnt for your exact model. But it is close. If you want the original instructions PM me and I will scan them. The only difference is oil bath vs greased bearings.

Later,

Jeff

SWAMPHUNTER45
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Re: RX7 drive unit question

Postby SWAMPHUNTER45 » Thu Jul 10, 2014 6:37 am

Cool that you got it apart and these guys were able to offer up some help!

gyrocopter582
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Re: RX7 drive unit question

Postby gyrocopter582 » Thu Jul 10, 2014 6:52 am

Akruff, the Mazda can be made to work very well on an airboat.
'Zoom-Zoom' on this forum has a well seasoned Mazda powered boat, that runs strong.
PM him, with any questions, he's good people.
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Joe863
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Re: RX7 drive unit question

Postby Joe863 » Fri Jul 18, 2014 10:44 am

Damn I want to put a rotary on an airboat so bad.

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jaxduramax
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Re: RX7 drive unit question

Postby jaxduramax » Sat Jul 19, 2014 12:47 am

It would be different yes but Rotary's aren't known for longevity are they? That's the good thing about LS, SBC, Lycoming, continental and the like, longevity.... Just my .02

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GTSIO-520
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Re: RX7 drive unit question

Postby GTSIO-520 » Sat Jul 19, 2014 8:28 am

Rotary engines a very durable if maintained properly. 200k is no problem on a rotary. They are susceptible to damage from over heating and carbon build up. But I don't see carbon build up as an issue on an airboat!
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Re: RX7 drive unit question

Postby Joe863 » Sat Jul 19, 2014 3:29 pm

Pretty sure I remember reading that Zoom Zoom has had his running on a boat for like 10 years.

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jaxduramax
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Re: RX7 drive unit question

Postby jaxduramax » Sat Jul 19, 2014 3:33 pm

Not to get is a pissing match but 90,000 is rebuild time on most rotary motors that are run hard. Over heating while airboating isn't unheard of especially when there are up to 5 different causal factors. And I don't know what you've been "driving" but 200,000 isn't a pile of miles now a days for most any conventional engine. These are my opinions based on my experiences. By all means, have your own perogative and run what you brung. Slide safe.

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ZoomZoom
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Re: RX7 drive unit question

Postby ZoomZoom » Sat Jul 19, 2014 6:49 pm

Rotary's only have 1/3 rd. the number of moving parts as your standard 4 cycle, much less to go wrong. In 1993 Mazda brought their rotary powered car to the 24 hrs. of La Mans, and won the race. Ingersoll- rand built some rotary's that were use as pump station engines, the engines ran for 23,000 hrs. on line, and when inspected the wear was so small it couldn't be measured. These engine weren't small you could walk thru the chambers. You don't have to like them, but by no means are they sub-standard to their 4 cycle brethren.













la

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BANANA BOAT
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Re: RX7 drive unit question

Postby BANANA BOAT » Sat Jul 19, 2014 8:54 pm

" All the other airboats go boing, boing, boing. But the Mazda goes hmmm"

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Whitebear
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Re: RX7 drive unit question

Postby Whitebear » Sat Jul 19, 2014 10:28 pm

Quite a lot have made their way into aircraft, both tractor and pusher configurations.
Image
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Re: RX7 drive unit question

Postby Joe863 » Sun Jul 20, 2014 11:20 am

ZoomZoom what reduction do you use? I have owned a few Rx7's and one day would like to do a 13b or 20b powered airboat.

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Re: RX7 drive unit question

Postby Ditch Baby » Sun Jul 20, 2014 11:25 pm

any videos of a rotary airboat? youtube doesn't pull up much. I want to hear what one sounds like.
'78 13ft Airgator 3/4deck, Lycoming O-320, 2 Blade Cypress Water Walker

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ZoomZoom
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Re: RX7 drive unit question

Postby ZoomZoom » Mon Jul 21, 2014 7:46 pm

Joe, the gears that I use in my gear boxes are planetary. The reason for this design, planetary gears have more than one point of contact. The big box has eight the smaller box has five. I also incorporate sparg clutchs in my boxes. What this does is to reduce the loads on the gears due to the different moments of inertia. The big box was made from parts of a Bell-47, and the smaller one uses parts from a Ford C-5 auto tranny.

Ditch, my rotary powered airboat is quieter than most because I use a five chamber aircraft style muffler that I built for it. Zoom

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emmitt Kelly
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Re: RX7 drive unit question

Postby emmitt Kelly » Tue Jul 22, 2014 5:57 am

Image
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gyrocopter582
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Re: RX7 drive unit question

Postby gyrocopter582 » Tue Jul 22, 2014 7:09 am

Zoom-Zoom is a bit modest.
He hand built both gearboxes using assorted parts, from helicopter gears, to automotive sprag clutches.
The 3:1 gearbox has run for years and years, and is about to move to another boat.
Bud modified the Mazda electronics to run out of the car.
He built an engine mount that tilts with hydraulics, to allow 'trim' adjustment while running.
He built his own stand, and rigging.
Oh yeah, he hand laid his own hull from a mold made by himself.
Did I mention, he is in his late sixties? :salute:
"Amaze your friends, annoy your neighbors"

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Whitebear
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Re: RX7 drive unit question

Postby Whitebear » Tue Jul 22, 2014 9:47 am

OUTSTANDING ! ! ! :thumbleft: :thumbleft: :thumbleft:
"The Constitution is not so the government can restrain the people, it is so the people can restrain the government." Patrick Henry
The government cannot give anything --
that they have not first taken from someone else.

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ZoomZoom
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Re: RX7 drive unit question

Postby ZoomZoom » Tue Jul 22, 2014 10:14 am

Mike thanks for the accolades !! We need to get back on skinny water one of these days, as soon as I get one of my boats running again. I'm like the cobbler who doesn't have a good pair of shoes to wear. I'll call you and we can swap lies. Zoom

Joe863
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Re: RX7 drive unit question

Postby Joe863 » Tue Jul 22, 2014 1:57 pm

That's awesome, Zoom is the man. Maybe one day I will have a rotary airboat out on the water.

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ZoomZoom
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Re: RX7 drive unit question

Postby ZoomZoom » Thu Jul 24, 2014 5:18 pm

Whitebear, if you know, do you have the e-mail address of the fellow who built the Cozy with a 13B Cosmo engine in it. I would like to ask him a couple of question about his engine installation, Thanks Zoom!

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Whitebear
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Re: RX7 drive unit question

Postby Whitebear » Thu Jul 24, 2014 9:51 pm

ZoomZoom wrote:Whitebear, if you know, do you have the e-mail address of the fellow who built the Cozy with a 13B Cosmo engine in it. I would like to ask him a couple of question about his engine installation, Thanks Zoom!



Sorry, I sure don't. Sure wish I knew him though !
"The Constitution is not so the government can restrain the people, it is so the people can restrain the government." Patrick Henry
The government cannot give anything --
that they have not first taken from someone else.


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