treedog

i know this is a dumb ? but how do i stop engine crank while tightening the prop nut
i feel silly using a balsa stick lmao

CRFlyer

I use a couple of rags and/or gloves to hold the prop with one hand while tightening the prop nut.

David Cutler

There should be less friction between the nut and the washer than between the prop and the drive hub, so just hold the prop (wrap it with a rag first, as they are sharp!) and tighten the nut as much as possible. If the shaft turns, then there is something wrong with the way the drive hub turns the prop, which could cause you problems in use.

-David C.

treedog

thx guys but theres gotta be a better way like a thin hex nut on the prop washer

treedog

or maybe a flat spot on the crank shaft to slip a skinney wrench on?

JohnBuckner

My Feedback: (1)

[quote]ORIGINAL: treedog

thx guys but theres gotta be a better way like a thin hex nut on the prop washer
[/quote




Proper spinner nuts are the best for a number of reasons especially when you are new.

http://www2.towerhobbies.com/cgi-bin...=RF&search3=Go

David Cutler

Please explain. Aren't you using the supplied nut and washer?

-David C.

BasinBum

My Feedback: (2)

It sounds like the prop is not fitting over the shaft and is only on the threads. If this is the case you need to drill or ream the opening slightly so it sits against the drive hub before bothering with a wrench.

treedog

yes im using original nut and washer its just that when im trying to start a cold engine and it floods for whatever reason and kicks back loosening the nut 4 or 5 times it just wears my patience out having to hold all that stuff together and retighten before ive even got it off the ground some times i'd just like to back the car over it and go home maybe i need a vallium or 2 lol

Montague

In theory, you could machine a flat on the prop hub. On some (but not all) engines this is keyed to the crankshaft. Then you could grab the hub behind the prop.

But it's not necessary. Really, grabbing the prop as the other guys have said is just fine, and it's what we've all been doing for years and years.

Once in a while I'll end up grabbing the hub with pliers if something happens like the prop blades get sheared off and the prop wasn't properly reamed out before hand.

treedog

theres an idea 2 flat spots on the hub then a skinney wrench might work montague or maybe a small hole drilled some where on the hub to stick a hex wrench into temporaily?

David Cutler

In decades of tightening nuts on engines I have never had to resort to grinding flats on the drive hub and certainly not on the shaft. My guess is that others have not had to either.

Holding the prop is a perfectly successful way to tighten the nut, and probably ends up with a lot more torque on it than relying on two flats on the aluminum of the drive hub, or weakening the shaft with large enough flats to be able to grip it tightly.

If the nut keeps coming undone, just tighten it tighter.

-David C.

treedog

thx all i guess ill end this now but i swear some day ill be accused of damaging a perfectly good plane with a caddilac and spend a nite in the box!

BasinBum

My Feedback: (2)

It sounds like your problem is with running the engine and not tightening the prop nut. You are looking to fix the sympton and not the cause. Having the engine backfire enough to back the nut isn't normal on a regular basis. If it is a four stroke you are probably leaning it out to much.

Montague

Personally, I wouldn't bother. Like the other guys here, I think you're fixing a non-problem.

I'm just saying it might be possible. Of course, on some planes, you can't see the hub anyway, it's often hidden by the cowl and spinner.

If you do decide to cut the prop hub or drill holes, be sure not to alter the crankshaft. And be sure to balance the parts if you remove much material. And make sure you don't reduce the contact surface between the hub and prop.

ctshepherd

My Feedback: (34)

If you want to get really fancy you can use one of these...


http://www2.towerhobbies.com/cgi-bin...?&I=LXKTM7&P=7

remove your glowplug and thread this tool in, it will contact the top of the piston and allow you to tighten the nut without anything else moving. Don't tighten too much as I've seen others punch a hole right through the top of the piston!

piper_chuck

My Feedback: (12)

I would NEVER subject the piston or conrod of one of my engines to the type of stresses this kind of thing is likely to cause.

ctshepherd

My Feedback: (34)

I suppose each person's mileage will vary! Properly used, they will not cause a problem.

Piper, what would be your solution to the original poster's question?

David Cutler

If you jam the piston in any way, and get anywhere near the torque on the prop nut that can be applied by just holding the prop and tightening it, my guess is you are well on your way to bending the con rod.

If you can't get the torque on the prop nut that's required then something else is causing the problem, like BB's suggestion that the prop is jamming on the thread and isn't seating properly on the drive hub.

-David C.

piper_chuck

My Feedback: (12)

Holding the prop with one hand and a wrench in the other hand has always worked for me.

BasinBum

My Feedback: (2)

That tool is a really bad idea for an airplane engine. It's a car tool from a car company and if you can't crank on it very hard without punching a hole in the piston than how would it solve the guys problem anyway?

Oh yes...nobody else seemed to notice that he's needing to get it really tight and redo it a lot because HE"S GETTING 4 OR 5 BACKFIRES PER START.

This is a classic case of putting a big band aid on the problem instead of curing the cause of the problem. Tune the engine so it doesn't back fire, problem solved.

piper_chuck

My Feedback: (12)

Actually, he said the engine "kicks back", not backfires. A prop that is adequately tightened should not be coming loose when an engine kicks back. It sounds like he's just not getting the nut tight enough.

BasinBum

My Feedback: (2)

If he wants to grind on the crank shaft I don't think he knows the differance.

gbzflyer

My Feedback: (2)

Treedog,

If you're using a wood prop, try a APC or Master Air Screw nylon prop.
I've seen the wood props loosen a lot more than the nylon.

Mike

stomper

My Feedback: (20)

If this is a four stroke engine, you will need a second nut called a jam nut on top of the first nut.