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05-26-2016 04:31 PM  3 years ago
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gt48

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Kingston, Ontario - Canada

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Broke conrod
Well the connecting rod on my 91srx broke and seized inside the engine. Damage: took a piece out of the groove in the case, so ring, piston, sleeve, pin, clips, and case need to be replaced. I was 2 turns out on both needles and was just 10 seconds into a hover at start of flight. Had about 1/2 gallon through it. I'm not sure what if anything I might have done to cause this, but not asking why it happened. Just mulling over my options and looking for opinions from more those with more experience with some of these engines. I bought the engine from rcjapan and I'm in Canada so I don't think warranty works for me but I'd love to hear thoughts on this.

My options right now are
1) fix the damn thing
2) get a new 91srx
3) get a new 96srx
4) get an os105 (then I need a new pipe)
5) use an align 91 my buddy has for cheap for now

Options 2 and 3 I priced at rcjapan and option 1 I priced at grandrc. After shipping and taxes options 1, 2, and 3 are all about the same price. So option 1 seems to be out for me based on cost. The questions I have are

i) Does the hatori pipe for the 91srx (SB-19FH4) work on the 96srx?
ii) What would you do?

The last thing I want is to blow another engine. If I break another conrod or break a crankshaft (I've read both of these things happening on the 91srx) I think I will shelve the heli (trex 700n) for awhile. I guess my post comes down to asking whether you would get another Tareq engine or cut my losses and move to something else?
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05-26-2016 05:51 PM  3 years ago
Eury

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Dover NH USA

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I was in a similar place when The crank on my 91srx broke about a month ago. In my case, the engine had spun unloaded at full throttle for a couple minutes in a crash and then it broke a couple of flights later so I blame myself.

The 91SRX is a great engine. It runs well and holds a tune well (at least it did prior to me driving it into the ground). I was going to order a new one and fix mine to have as a spare until Tower sent me a great coupon and I found a ridiculous deal on a pipe and bought an OS105HZR.

Having run both, power is a wash, as is tuning. They are both great. The OS with Powerboost pipe sounds terrible, while my YS with Hatori sounded great. Fuel consumption is similar with the YS using a bit less. Vibration wise the OS feels a tiny bit smoother. The only real advantage in the OS in my experience is that Glow plugs last a long time where the YS would only like expensive Enya plugs and kill them every gallon or so.

If I could go back I probably wouldn't have bought the OS. I spent a lot more money for no real gain. If I were in your shoes I'd get another YS and keep yours for parts. 96 vs 91, personally I don't need the extra power so I'd go with the 91 and save some cash and have more parts that can interchange. I was never able to get a clear answer on my 91Srx Hatori going with the 96, my feeling is it'll work but not be ideal but I have no real data to back that up.
Nick Crego

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05-26-2016 06:53 PM  3 years ago
utahbob

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St. George Utah

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just a thought..
Is the anti-rotation pin (for the ring) seated to deep..letting the ring rotate?..it almost cost me a problem once.
I do a great decending funnel!
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05-26-2016 07:33 PM  3 years ago
gt48

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Kingston, Ontario - Canada

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Thank you, Nick. I'm tempted. If I could pinpoint something I did that led to the conrod breaking I'd go for another 91srx for sure since I'd know what not to do. Still mulling I guess. For now I think I'll run my buddy's align 91 and send an email to YS Japan. Utahbob, I don't know the answer to your question, but will be sure to check if I get a new one.
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05-27-2016 01:25 AM  3 years ago
payne1967

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uk

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did you use a crank locking tool when you fitted the fan hub/crank nut to the engine?
if you you may have bent the con rod and this may have caused the failure
I did it once on an os61sxhwc
www.alcesterhelicopterclub.bmfa.org
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05-27-2016 02:43 AM  3 years ago
gt48

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Kingston, Ontario - Canada

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Pretty sure I used a plastic toothbrush when I tightened the nut. I suppose it's possible that the conrod bent then. I'll be sure to watch for that in the future. I wouldn't have thought that could bend the conrod.
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05-27-2016 01:44 PM  3 years ago
JuanRodriguez

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The Villages, Florida

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did you use a crank locking tool when you fitted the fan hub/crank nut to the engine?
if you you may have bent the con rod and this may have caused the failure
I did it once on an os61sxhwc
Not sure I understand your comment.....

Using a "crank lock tool" (the one inserted through the back plate) takes all of the pressure off the connecting rod when tightening the nut as it locks the crank.....

I may be misunderstanding what you said, though......Did you mean to say "if you did not, you may have bent......"

Using a toothbrush to lock the crank through the back plate accomplishes the same thing.... If that was done, no pressure is placed on the rod itself.....
Been there, done that and old enough to know better.....
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05-27-2016 05:21 PM  3 years ago
Four Stroker

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Atlanta

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The usual reason for breaking a crank later after the fact is trying to crank a flooded engine with a mongo starter - say a Dynatron on 4S or more.

All crank lock tools put stress on the rod. That's how they lock.
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05-28-2016 12:20 AM  3 years ago
payne1967

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uk

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Using a "crank lock tool" (the one inserted through the back plate) takes all of the pressure off the connecting rod when tightening the nut as it locks the crank.....

I may be misunderstanding what you said, though......Did you mean to say "if you did not, you may have bent......"

Using a toothbrush to lock the crank through the back plate accomplishes the same thing.... If that was done, no pressure is placed on the rod itself.....
Been there, done that and old enough to know better.....

if you have the piston at bottom dead centre then the crank locking tool
can put pressure on the con-rod
at top dead centre only the big end of the con rod is in contact with the tool
www.alcesterhelicopterclub.bmfa.org
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05-28-2016 12:38 AM  3 years ago
JuanRodriguez

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The Villages, Florida

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Sorry but I don't see how using the crank locking tool puts any pressure on the connecting rod at all . The tool locks the crank and does not come into play with the rod at all . That is the purpose of the tool . Been using one for a long time but maybe I'm missing something. I've never had a con rod get damaged while using the tool.../Been there, done that and old enough to know better.....
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05-28-2016 01:46 AM  3 years ago
Eury

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Dover NH USA

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That's been my experience as well. I've had an OS crank lock tool for probably 20 years and it's never damaged anything. The rod has 0 pressure on it with the tool.

Regardless, The question I have is how would you hold the crank still while tightening the nut if you don't use a crank lock tool, especially if you don't like the toothbrush trick?
Nick Crego

Citizen #0168
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05-28-2016 01:08 PM  3 years ago
wjvail

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Meridian, Mississippi

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Hummm... Using a backplate crank locking tool does put some pressure on the rod. I use these tools all the time and recommend them but there is some force transferred to the rod.

If you don't believe me, trying using one without the rod installed. I've made the mistake of removing the sleeve/piston/rod before breaking the fan nut loose leaving only the crank installed and I can tell you, this tool is rendered useless! Try using one with the rod installed but no piston on top of it.

There is some force being applied to the rod.

Bill
"Well, nothing bad can happen now."
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05-28-2016 01:28 PM  3 years ago
wjvail

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Meridian, Mississippi

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One more thing - before I forget - be very careful using a crank locking tool on an OS 1.05.

The skirt of this piston is very thin and extends a long way into the case at BDC. The skirt will hit the locking tool first and applying torque to the fan nut will transfer the forces to the piston distorting the skirt. I had to take my locking tool to the belt sander and remove material to avoid damage.

I can't speak to other engines but I'm certain the OS 1.05 can be damaged.

Bill
"Well, nothing bad can happen now."
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05-28-2016 05:07 PM  3 years ago
gt48

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Kingston, Ontario - Canada

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Does anybody know if the 3ds and srx crankcases are the same?
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