Sticking piston

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js78

js78

Member
Messages
24
Location
Canada
Hey guys/gals, I finally got to fire up my savage SS today and things were going well for the 1st tank (good temp, decent idle, etc), but when the fuel ran out the piston got stuck at the top of the cylinder. Jester gave me some quick help via the chat (thanks again) and I pulled the engine off and rotated the piston down by the flywheel.

But heres my problem, whenever I turn over the engine with the flywheel it gets stuck again at TDC and then the flywheel starts slipping! I took apart the clutch and noticed that the nut that holds the flywheel down screws on clockwise but the engine turns counterclockwise so when the piston get stuck at TDC and I try to rotate the flywheel it ends up unscrewing the nut because the tension in the cylinder is so high. Is that how tight these engines are until the brake-in is over? The pull start wont even cycle the engine once fully because the piston keeps getting stuck.

I cant wait to get this thing running, all I want is to see my truck soaring gracefully..... over my roof that is.....
 
I would say you need to tighten the nut down more .. when you shut down the engine .. make sure you put the piston at Bottom dead center .. especially during break in .. when the piston is at bottom dead center Mark the flywheel so you know where to have the piston ..
 
if mines been sitting for a fairly long time i always use a bit of after run oil so the first start isnt a dry start "no lubrication" and i do it first start on my new engines as well, don't know if its any better to do it this way but thats how i do it!! because i figure nitro engines depend on the fuel to lubricate it so until the fuel reaches the cylinder its pretty much metal on metal this might help a bit preventing it from sticking at the "pinch" point I'm not sure
 
hmmmm, ive put a good amount of AR oil in the engine to let it soak for a bit. I'm prety sure the bolt is fully tightened. I just don't understand why the engine is so tight that i cant even pull the pull start. I even took off the pull start to make sure it works properly.
 
so ive had the motor by a heater for a little while, its at 130F, and I can actually turn it over by hand now with the flywheel. I think you might be right Jester, so I'm gonna grab a heat gun and try to fire her up tom. Thanks for the help!
 
A heat gun works wonders!!! After run oil is a good lubricant but I wouldnt recomend it on a new engine as it may cause a hydrolock and end up getting stuck again!! Or even worse causing stress on your con rod and pull start if ur yanking on it!!Loosening the glow plug is a great idea as long as the head is clean especially around the plug!! Good Luck Bud!!
 
One thing to add. Use red locktite on that nut. Not alot or it is a bear to get off, but if you use blue the heat from the motor makes it pointless. Red will hold up better to the temps. Also useing a heat gun to heat the motor while at bdc is a very good idea during breakin. If I remember right most people heat to about 200 degrees before they start.
 
Well i had some mixed results today. I managed to heat up the engine nice an warm with the heat gun and fired up the engine. While its on the box the wheels spin quite a bit, I'm guessing the factory idle is set quite high? Strangely, have to give it a tiny bit of gas otherwise the engine cuts out. So i went to do some circular >1/2 throttle driving but every time i press the brakes the engine dies. I'm trying to follow the manual but i think i must be missing something here.

Heres a pic just for fun:
IMG_1146.jpg
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I had the same problems. Mine was a combo of the linkage being out of adjustment and the stock clutch shoes being crap. I changed the shoes to nova ones and adjusted the linkage. You want to set it so that when you hit the brakes it does not push on the carb.
 
mine did that as well and what i had to do was take the air filter off to inspect the gap in the carb, which i found out there wasnt one lol so u adjust the idle screw till theres about a 1mm gap when brakes are applied this will help keep it running while braking
 
Disconnect you linkage and apply slight pressure to the end of the carb slide to make sure it is up against the idle screw. Then adjust your idle gap by looking down the intake with the filter removed. Approx .75 - 1.0mm will be fine. Now you can reconnect your linkage. So now even if your linkage is not set quite right, it still can't close your carb. You still need to make sure you set it up properly though, so your not over stressing the servo when it should be at rest.
Hope this helps.
 
Thanks for the help guys. Things went well today, the sticking piston problems seems to have been resolved. I had the truck out for a while doing some figure eights in a local parking lot. I checked the carb and their is a 1mm gap so i think thats ok, but I'm a bit confused here. My wheels spin b/c the idle is set to high, but the truck dies when I stop completely meaning the idle is to low?
 
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I think ive diagnosed my idle problems as being a clutch problem, it seems as though its grabbing all the time, I'm gonna pull it off and have a look tonight.
 
That is what I was talking about. Mine did it too. The stock shoes are garbage. Replace them with some nova clutch shoes and you will be totally satisfied.
 
Ya thatnks CrawlinClodKiller, you were right. My clutch shoes were really tight so i to the clutch apart and made sure everything was installed correctly. The clutch bell is looser now. But should it be loose enough to spin freely (a couple of revolutions) or just loose enough to turn by hand?
 
It should be loose enough to spin VERY freely like a bike tire when bike is upside down. You should feel a bit of clearance fore and aft kinda like a proper spur gear mesh and ring and pinion backlash.

Dave
 
Hi,


As the motor gets broke in the problem with the shoes will go away, they wear. I just used the stock shoes then bought some Nova shoes later.

If you get Nova shoes you can ask ][op about getting them and get a discount (I beleive thats still offered). The forum has quite a few vendors, some offer nice discounts and other deals to the members here.

Here's a link to the vendor's sub forum. https://www.hpisavageforum.com/forums/forumdisplay.php?f=95

Oh another thing about the Nova shoes (BTW most people love them) when you go to buy them you will be best to buy different springs and pilot nut, you can the part numbers and other great info about them in Jesters Nova shoes review it is a very detailed review, heres a link

https://www.hpisavageforum.com/forums/showthread.php?t=3319

the tightness at the top of the piston is called the pinch if I am not mistaken, it will get much better after it is broken in properly, it takes a little time but not too bad, you will also see the power increase as the motor comes to life.

One last thing, Welcome to HPISF!!
 
ShiftPoint said:
the tightness at the top of the piston is called the pinch if I am not mistaken, it will get much better after it is broken in properly, it takes a little time but not too bad, you will also see the power increase as the motor comes to life.
Click to expand...

Some people do call that the "pinch". These cylinders are not like ordinary car cylinders. They actually reduce in diameter at the top. So it's shaped more like a cone. The "pinch" spot is where you'll have the highest compression. Breaking in the motor correctly will provide a good clean pinch spot for longer run time of the motor. Improper break-in can actually cause premature wear on this spot causing less compression from the engine. This can cause a loss in power and life of the motor. This is why breaking a motor in with a rich setting is so important. The less wear you put on the pinch in the beginning, the better off you are! :)


Welcome to the forums js78!!! You're sure to have fun with that new truck too! :)
 
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Thanks guys ive had the truck out a couple of times since the break-in and I was amazed the whole time (Its my first nitro). This truck is awesome, great forum by the way!
 
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