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09-15-2009 03:37 PM  11 years ago
pgkevet

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Wales

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I don't think it is about trueness. I think it is about balance with the piston. Since the piston and crank counterweight are rotating, the point at which they balance is dependent on engine rpm.
I assume that interesting idea is dynamic balance with the g-force of the piston to reduce harmincs?
Crank can be considerably untrue. It is just pressed together. Mine was out .007 inch before I sent it to Hanson. It came back less than .0005. He also did other things to it and it is very smooth runing now.
Where are you measuring this 'trueness'?.. just rotation with a gauge to the side of the tip at slow handspeed? Because I can unserstand that as a selling point but it doesn't equate necessarily to trueness across the bearings and side-flutter. I accept that it's a starting point.

I'm not having a dig here ..just trying to get an understanding of what is rally offered and how much benefit it really has..

I knw that when i checked the runout of my crank then the crank itself was near perfection on the stock engine .. but getting the fan on without runout was another matter..either an offset of the centre drilling or the fan itself..
pgk
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09-15-2009 05:09 PM  11 years ago
chilibean

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cape may,n.j.usa

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trueness
I'm not sure what you mean by across the bearings but the crank is held in place by the bearings at each end so the trueness shows up at the ends of the crank. I measured at the fan end at the tip of the taper. My fan also was not true but after much fiddling I got that to less than.0005 inch also. I think what you are paying for is experience. I tried to straighten one myself. I spent two days on it but did get it in the end. Al at hanson told me he does it in 15 nimutes or less.
I'm still having issues with the heli but don't think they are engine related.
Paul
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09-15-2009 05:20 PM  11 years ago
pgkevet

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I'm not sure what you mean by across the bearings but the crank is held in place by the bearings at each end so the trueness shows up at the ends of the crank.
My stock crank had no runout at the fan end taper top.. (that my dial guage recognised anyway)..so it must have been maginal it at all. But I was also able to move the crank within it's bearings with gentle side-forces.

What I was trying to suggest is that trueness should be attention to the concentricity of the centre thread and the taper and the bearing points...The way the crank goes each side of the centre casting makes me wonder about both ends of the crank being in alignment as well.

So a really balanced and trued crank would be cnc machined in one hit once the basic block was assembled. If you start taking metal off the assembly as provided then that has to include altering the bearing points?

(I'm just sorta thinking about this while I doodle here)
pgk
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09-15-2009 05:38 PM  11 years ago
carpman

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Spain

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Wow seems every problem at the moment turns into a scientific exploration, so I get lost very early on...

..time to go fly....
KEVIN
Trex 500ESP | Trex 600NSP | Trex 700 Gasser | MA Spectra G
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09-15-2009 05:46 PM  11 years ago
AceBird

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Utica, NY USA

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the point at which they balance is dependent on engine rpm.
Because the crank is rotating the engine will never be in perfect balance but will be best at specific RPM’s. Even a twin cylinder is not perfectly balanced but gets damn close.
Ace
What could be more fun?
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09-15-2009 05:47 PM  11 years ago
AceBird

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Utica, NY USA

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but getting the fan on without runout was another matter..either an offset of the centre drilling or the fan itself..
I don’t see how the crank could be out either because I am sure the taper is ground on centers after the crank is assembled but that is an assumption on my part. I do agree that the mounting of the Century fan is the issue for two reasons. I don’t have experience with other makes. 1) The fan is aluminum and being soft it can be distorted in the first attempt to assemble it to the crank. 2) The taper doesn’t go on far enough. The length of purchase should be 25% greater then the diameter of the small end of the taper to prevent cocking during assembly.

As some of you know I machined a tapered hub out of steel so the contact is steel on steel for a longer distance (almost the full length of the taper on the crank). This gave me a face plate where I could shift the fan x and y through oversize holes in the fan to get it concentric without beating it. It would be a great part for smallplanes to mass produce if he wanted to. The only problem is you have to modify the fan hub also to use it.

Ace
What could be more fun?
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09-15-2009 06:05 PM  11 years ago
pgkevet

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I don’t see how the crank could be out either because I am sure the taper is ground on centers after the crank is assembled but that is an assumption on my part.
..which leads right back to the question...if being sold a modded engine on grounds of a trued crank (as well as ported etc).. then what is really being trued?
pgk
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09-15-2009 07:09 PM  11 years ago
shawmcky

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Isle of Wight,United Kingdom

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Truing
Usually refers to the exact alignment of a two part crankshaft around the centre pin .Most singles are two halves pressed together.Most two stroke tuners make this one of the first jobs on the list of corrections if necessary.
Team- unbiased opinion.K.I.S.S principle upheld here
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09-15-2009 07:16 PM  11 years ago
pgkevet

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Wales

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A meter on the engine

Finally got around to it..

EDIT
I cannot pick up any voltage across the spark boot to engine when cranking. I can't get any significant voltage across the red wire from the red coil to the engine block when cranking. I did think a coupe fo tiems i was picking up about a volt.. but that may have just been vibration through the bench when I was cranking.

I can;t show continuity through the coils.. but thinking about this there has to be two coils inside each if they are upping voltage so the wire in and wire out aren't continuous..they are from separate coils?

Anyway. I get circuit from red coil black wire to engine. No circuit from red coil red wire to engine. Circuit from red wire grey coil to engine but no circuit from boot wire to engine.

Is this high resistance in the seccnd stage coils or two dud coils?
pgk
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09-15-2009 07:19 PM  11 years ago
shawmcky

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Remember the argument
about using piston stoppers,it is quite easy if you are a bit of a gorilla to twist the halves out of true
Team- unbiased opinion.K.I.S.S principle upheld here
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09-15-2009 07:43 PM  11 years ago
pgkevet

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about using piston stoppers,it is quite easy if you are a bit of a gorilla to twist the halves out of true
OK I can see and understand that...
pgk
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09-16-2009 10:06 AM  11 years ago
pgkevet

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Wales

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Anyone got a proper method of testing the coils?pgk
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09-16-2009 10:57 AM  11 years ago
shawmcky

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pgkevet
if you look in your Zenoah manual under IGNITION SYSTEM it shows exactly how to test both source and ignition coils and the values you are looking for.Sometimes the spark is very hard to see in daylight try a dark area.The source coil resistance is either 185 or 255 ohms depending on the part number.
Team- unbiased opinion.K.I.S.S principle upheld here
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09-16-2009 01:41 PM  11 years ago
pgkevet

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D@mn - the old RTFM, eh?

As it happens I 'cheated' and chatted to my local Garage this morning and got told how to check....

But since I'm unhappy with the condition of the piston top.. and it really isn't worth the time and invetsment in parts to strip donw a stock engine and overhaul it with the costs of a source coil, possible gaskets and the rest..compared to a new stock engine.. I'm still swayed towards anew modded one..

Mind, with the wind gusting well into the mid 30's today (again)...It'd be nice to find somewhere that wasn't on top of a hill to fly!
pgk
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09-16-2009 01:49 PM  11 years ago
shawmcky

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pgkevet
Pull the cylinder off and make sure it is not just a sticky piston ring.Can be a common problem.
Team- unbiased opinion.K.I.S.S principle upheld here
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09-16-2009 03:21 PM  11 years ago
pgkevet

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Pull the cylinder off and make sure it is not just a sticky piston ring.Can be a common problem.
If it pulls happily and it looks fine through exhaust and carb ports - even if it was a sticky ring.. how would that affect spark? Surely if the flywheel goes round and has it's magnet then a current should be produced unless source coil is dud?
pgk
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09-16-2009 03:29 PM  11 years ago
Fixit

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UK

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PGK
Just buy a new one and send that one to me for a restoration project, you know I will put it to good use
I only like to fly gassed up
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09-16-2009 03:40 PM  11 years ago
shawmcky

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pgkevet
No bearing at all on your spark problem.Your talk of replacing the engine ,even though your piston/ring may look like new from the inlet,it could still have a sticky ring.Did i read that you had a lot of carbon build up or was that another postI recently popped a cylinder off a friends under performing gasser/hard starter the piston looked like new through the inlet port as did the ring,lo and behold when the cylinder was removed the piston and ring still looked like new but the ring was jammed solid,but it still ran reasonably well,this is not the first time i have seen this problem occur.
Team- unbiased opinion.K.I.S.S principle upheld here
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09-16-2009 04:31 PM  11 years ago
pgkevet

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Wales

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Carbon build up on the piston top... viewed through the pluhole. Why it seems pointless buying parts for this compared to a new stock engine.. the source coil is 1/4 the price of a new stock engine alone.

Fixit

Whatever i decide I'm going to end up taking this one apart.. just for the experience. Then it'll either be spare parts or in a bag to you since my spares bins are taking up rather a lot of room..
pgk
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10-12-2009 06:00 PM  11 years ago
pgkevet

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Wales

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I decided to go with a new engine.
Along my research I spoke to Ian Oddie..Oddified Motors. After 2 emails I got a reply.. enthusaistic and very promising with his claims for what he can do.. which apparently also involves some small mods to the carb to widen the RPM range for heli use.

Then it took him 4 days and 6 further emails before I got another answer and a promise that he would build the engine a week later.

2 weeks went by and then 4 days of emails with no response..So I wrote and pointed out that it doesn't matter if he has the best engine in the world.. he certainly has some of the worst customer response and support and we're through!

I had hoped that a supplier on the same landmass would be able to help hands on with stuff if necessary.. and he had claimed to build these, run them in, dyno them and send them carb set close to best usage. He also claimed to get close to 6HP with a tuned pipe...

However Al Hanson answers within a couple of hours and will be sending me an engine this week (which will then sit in customs for 2 weeks)...
pgk
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