Sport_Pilot

Well that explains why some Pro 40's preform like a .46 and some don't! Or at least some have claimed so, and other say this is not so! This is to say that maybe this has happened before, but nobody noticed.

THRL-CKER

My thinking is that Hobico / Tower may be getting ready to discontinue the TT 40 Pro and are using up extra parts.

dphill2

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Could it be that they are selling the 40s and not selling the 46 !! so this is a way to get rid of the 46 inventory[:@]

Dave..

BarryReade

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I am the only one at my club that has PRO 40's.  Everyone else has PRO .46's and there are lots as my club has upwards of 200 members and I am the only pylon racer that I know of.  Why buy a 40 when for $10 more you can get a 46.  I really think it is the other way around Dave.  Not that I am happy with my assessment but the sport fliers want the 46 and there are a lot more of them than racers.

dphill2

My Feedback: (1)

Barry,
We have 125 members in our club And I could count the 46s on one hand !! As a matter of fact I don't know of a member that is flying a TT46. There may be some but very few, I know several flying 40s and every one of them Fly Club-40.
Just between my son and I, we have 7 TT40s, and Almost every person that has a Club-40 racer has at least 2 motors if not more...

Dave..

BarryReade

My Feedback: (1)

Wow, that is the difference between clubs as we don't have any racing at our club yet.  I did see an Enya 40 the other day it I was surprised at how strong it ran.

BarryReade

My Feedback: (1)

Well, Crapola!! Just when things seem to be stable now we have to deal with this.

Noff

So far from what I see in this thread nobody has offered any evidence that there's been a mix-up at the manufacturer or distributor and .46 parts have been installed into .40 engines. This is possible but highly improbable since the crankcase, piston, cylinder, and crankshaft are all different between the .40 and .46 engines.

The difference between the .40 and .46 engines that are related to displacement are the bores and strokes of the engines. The .40 has a 20.9mm bore and a 19.0mm stroke where the .46 has a 21.8mm bore and a 20.0mm stroke. We're talking around 1mm difference for each.

Measuring stroke through the glow plug hole is highly inaccurate - there is no solid 'footing' for calipers to rest on with the fins on the top of the head and no way to tell if your calipers are perpindicular to the top of the piston. I tried this myself on an engine and got wildly different measurements after doing the same measurement three times. In addition to get a stroke measurement, you have to get a measurements at bottom dead center (BDC) and top dead center (TDC) and then subtract to get the stroke. With the head on, you cant really see where BDC and TDC is further adding to the inaccuracy of a stroke measurement. The only way to do this properly is to remove the cylinder head, which incidentally allows you to check the bore of the engine as well.

I removed the head from a brand new Thunder Tiger Pro .40 and this is what I found:
piston at BDC to top of cylinder sleeve: 23.08mm
piston at TDC to top of cylinder sleeve: 4.22mm
This gives a measured stroke of 18.86mm. Thunder Tiger says the stroke is 19.0mm. Measurement error and manufacturing tolerance would account for the difference between spec and my measurement easily.
I measured the bore and got 20.89mm which is almost identical to the 20.9mm bore spec. This is all measured with $40-ish digital calipers. I wouldn't expect the accuracy to be great with these calipers (measurement error due to equipment) but this all jives pretty closely to the specs at http://www.ttamerica.com/engines/ttrg1140.htm

Just for fun, I calculated displacement using my measurements.
The formula for the volume of a cylinder is Pi * Radius squared * height.
Converting my measurements to centimeters (to have a final answer in cc / cubic centimeters) and plugging in my measurements I get (3.14192654 * (2.089cm/2)^2 * 1.886cm=6.464195706), which after reasonable rounding is 6.46 cm^3 or 6.46cc, slightly lower than the 6.52cc spec and way lower than the .46 displacement of 7.47cc. I'm awful darn sure I have a .40 cubic inch displacement in hand.

As far as I can tell, looking at the gap between the head and the crankcase only gives you an indication of the compression ratio of the engine. I can stack 20 head shims under the head and the bore / stroke of the engine will not change - the bore is still the same and the distance the piston travels up (or down) in one rotation of the crankshaft (which of course is the stroke) does not change either. These things are built into the engine and independent of cylinder head height. Perhaps Thunder Tiger is machining more material away under the cylinder head or is making them from a little shorter billet aluminum which would account for the differences that some people have noticed earlier in this thread.

If someone has a new engine that really does have the wrong parts inside, then I'm sure that Hobby Services (the warranty center for Thunder Tiger) or the distributor will take care of you. Just truly be sure that you're sure that it really is a .46 in a .40 box. Looking at the box, head clearance, etc does not definitively determine that something is wrong. You have to look inside and check with a reasonably accurate set of calipers.

bjr_93tz

I think the point is that they're not trying to accurately measure the displacement, but identify if the wrong size part has been installed.

Think of the calipers as being used like a go-nogo guage. Close to 19mm stroke (+-.25mm) and it's probably a .40 sized crank, measure closer to 20mm and it warrants a closer look.

THRL-CKER

Noff, this is not a accurate measurement, but it is close enough to see that there is a problem 1mm is approximately 1/32 of an inch and can easily be seen with the naked eye.

as the engine that I looked at it was new in the box at the LHS and we did not want to tear it down. The engine Tim bought in DFW area was torn down and compared to a known TT40 that was also torn down. They did not have measuring equipment to check it against the specs, but they said the 40 piston would rattle around in the 46 sleeve.

As this is a tapered bore I don't know where they are measuring the bore from or how much of a taper it is. If it is an even taper I suppose you could measure it at the BDC and again at TDC and average the bore dimension.

This was not meant to be anaccurate measurement, but something that could be checked at a race with minimum equipment. Something in the line of the gage used to measure tread depth on tires will work if it is long enough.

Oldbob

Noff using a dial caliper to accurately measure the stroke is the wrong tool. This tool will give you only a close approximation, but close enough to tell the difference of 1 mm. Use the dial caliper to measure the bore and it will give you an accurate reading of the bore. You need a dial depth gauge to accurately measure the stroke. This is a different tool, go get one and you will be able to accurately measure the stroke through the glow plug hole. With these two tools I can measure the stroke and bore to within .001 inch. Close enough to accurately determine the engine displacement.
Bob

dphill2

My Feedback: (1)

Guy's
I could not stand it, I took both motors apart and checked them against each other !! the only thing I found was one had more pinch than the other and they had different rods . One had a very small lite weight rod and the other had a very heavy rod that had oil holes drilled in the crank end ! I'm going to take both to a buddy machine shop (he is a modeler also) to check both.
Dave..

Oldbob

"Well, Crapola!! Just when things seem to be stable now we have to deal with this.

Of course we can always blame it on Old Bob!! Or Jim, Dave, Tim, etc. You are all guilty and you know it!!!"

Berry, I’m getting too old for this kind of distraction in the sport I love. The only reason I race is for the 1:30 minutes of adrenalin during the actual race. Win, lose or draw I am having a ball during the race. However, distractions like this engine crap have me wondering if it’s worth it. We will have to wait and see what effect this engine situation will have on Club 40. See you in T-Town
Bob

BarryReade

My Feedback: (1)

Bob, I understand completely. I felt the thread was just getting to uptight and added the levity to try and loosen things up.

The old saying "what is, is, so deal with it" is what we have to do. If we get lemons I want to make lemonade.

Dave the rod on top is the new design that has been out for a couple of years or more. the lower solid rod without the flutes or oil holes is a really old design. I seen motors that really ran strong and lasted a long time with both style rods.

dphill2

My Feedback: (1)

Hey I'm Happy with what I found !! Both motors seem to be the same, as far as I can tell !!

Dave..

Tbatt

My Feedback: (4)

I checked my NIB engine last night and it is a 40, whew!

Lets put our heads together and see if we can come up with a simple way of checking the engines at not only tech inspection, but at home before the race.

We need to be careful here so we don't scare anyone away from Club 40 because the engine supplier has gone whacky....

Tim

BarryReade

My Feedback: (1)

Measuring the bore and stroke is the only way as i see it.  A dial caliper for the bore and a Dial indicator with a 1" travel would do the stroke.  It would involve removing the head but, there would be no doubt in anyone's mind if the motor was a legal .40 displacement.  It would seem that for $50-75 for the two instruments would be sufficient to purchase both unless someone already has them.  The major issue is determining the actual measured dimensions so as to make it uniform throughout the community.

Oldbob

Barry the booklet that comes with the PRO Series engine has all the dimensions on page 3 for each PRO Series engine, from their .25 up to the 1.20. My three engines measure to within .001 inch of the dimensions given for the 40. We should use the dimensions given in this booklet.
Bob

airraptor

My Feedback: (66)

For you guys i know you have been doing this for a long time but why not just change the rule to all 46 size engines. you will not see that much gain in speed maybe 3-5 mph. doing this will allow you have a 46 size engine and will open up other venues like the T-34 races that allow a 46 size engine. just a thought. the rule change would be a sore subject for guys running the "40" but i think it would be the best route to go. there are not many other "40" size engines out there. you can make it where the guy running a 46 engine to limit prop size or something like say a 11x5 prop to keep it in the same power range as the 40.

skull1971

I like this idea, something to think about.

BarryReade

My Feedback: (1)

Bob, bring it up to Ken and the rest of the RCPRO Club 40 Rules committee. I think that would be best.

Tim, we need your input on that from your guys also.

dasintex

My Feedback: (10)

I had suggested this very proposal previously in a heated and lengthy discussion here on RCU last year or the year before, when we were talking about Tweaking -vs- Cheating and my decision to get out of racing because both were going on, if you went to 46 size eliminates some issues and it creates more choices for engines: Magnum, TT Pro, OS, etc. However, opens the door to more manipulating: Magnum 52 parts into a 46; OS 55 parts into their 46, not sure if either is possibe.

Another quick question, do you think the change in engines by Thunder Tiger occurred at the same time they changed the Muffler Baffles?

Oldbob

Barry this is not a rules issue and I don’t think the rules committee needs to spend time dealing with it. This is a “verification” of an existing rule which needs to be handled by the CD of an event. We will have a race in Hico Texas this Saturday and the CD, Gary Fisher, will have all engines in the A-MAIN inspected by removing the Head. I will provide the Dial Caliper and Depth Gauge. And we will be using the dimensions that are published in the TT PRO booklet. If anyone wishes to have their engine looked at before the race I will do that for them.

As for running the two engines in the same race I think we need some volunteers to do some racing with the 40 and 46 in the same heat. According to the numbers published in the TT booklet, the 46 has 17% more horsepower than the 40. IMHO this is significant and I don’t think the 40’s can keep up with the 46’s. But we need to test this before we jump into a boiling kettle on fish.

Bob

THRL-CKER

Bob, I remember that Fred French had a dial indicator with an adapter on it to fit the glow plug hole, and I think it gave one to someone else but I do not know who has it. At the time Fred was suggesting this to be used to check head shim thickness, and I did not see how that would work because changing head shims does not change the stroke measurement. It would work however to check the stroke I could probably make one, I have two dial indicators that could be used. This could be done at the pre-race inspection and wont take long. If you want to remove heads you better have a drill because some head bolts will strip out the head ( of the bolt ) if they have been on for a long time.

Another solution is to do what I suggested a few years ago when cheating was suspected. And change the whole set up and go by break out times. Having a Gold, Silver, and Bronze class.
After establishing what the 100 MPH break out time is for the 400 foot course anyone going under that time is disqualified for that heat. Then taking the total times for the heats break the entrants into Gold, Silver, and Bronze class.

In doing this everonewill get to run in a main event and can fly a plane of the speed they are comfertroble with.

This could even open it up to additional airframes and engine types and sizes.

This would totally eliminate the "Cheating " issue no matter if you are talking engines airframes or what ever.

I know this is a drastic change, but give it some thought.

Tbatt

My Feedback: (4)

I agree with OldBob. All we need to do is figure out how (we know that) and then enforce the rules. Going to a 46 size engine will really set some of our guys off. I myself have five engines that would be obsolete if we went to a 46. That would be expensive!

Harbor Freight has some very low cost measuring tools. I picked up one of their digital calipers for less than $20 and it is every bit as accurate as my $200 Brown and Sharp (Swiss) calipers. They have dial gages too.