foxfloat

OK so i just started to break in my hyper 7 i ran 2 tanks of gas through it just idling and on the second tank i just let it run out of gas and then 30 minutes i tried starting it again the pull start was locked up and i took apart and found out that my piston was seized up. dose anyone have any idea why? should i just turn it into my factory warranty?

youwish16

im guessing that when you turned it off, you didnt check to make sure the piston was at bdc? always makes sure its at bdc before you let it cool. the sleeve expands when in use and if you let it cool with the piston at the top of its stroke, when it contracts after cooling it will seize up

foxfloat

what dose bdc mean?

romax

Bottom Dead Center. When you shut off the engine always make sure the piston is at the bottom of it's travel. The sleeve the piston sits in is tapered at the top, making a tight fit. I would suggest getting a heat gun & heating the engine to around 200 degrees , the piston should hopefully move then. Whatever you do don't force it as it could cause damage.

ace9213

get a temp gun when breaking in the engine. that will help. your engine hasnt seized from the sounds of it. just has a ton of compression. loosen up your glow plug and try to pull the pull start

foxfloat

i took the glow plug out and the pull start still wont move so I'm going to try the heat gun and see if that works

foxfloat

i called the ofna tech support they said that since i ran it dry and the fly wheel is totally locked up that theirs nothing they can do for it. and i tried the heat gun. dose anyone else have any ideas.

ShoestringRacer

you said you took it apart, did you take the head off and see the piston stuck in the sleeve?

the heat gun should work, you need to heat the top of the case, not the cooling head, the case all around where the sleeve is - that will expand it and you should be able to free the piston.

if that doesnt work you can take a wood dowel ideally or some other item that you can use as a drift through the glow plug hole and gently tap it to push the piston down. wood dowel is best because you wont damage the piston but I have used a flat punch with gentle tapping is ok too.

you can also take the head off and try to use something to push the piston down. if you take off the head you can try to heat the case again and also use a drift and together you should be able to get the piston free.

djzachtyler

My Feedback: (4)

sounds to me like you have few available options...

here's some tricks I have used...

1) remove the clutchbell, shoes, and pull starter then get a socket wrench and try to gently turn the thing over using the added leverage. do not over torque things as you can easily snap the con rod. also make sure you have some penetrating oil on hand...

2) this is not the best idea as you can seriously damage the internals of you are not dead careful, but you put the engine in a vice (I use shop towels for padding) and gently make sure it is seated without being pinched. next take one of those flat ended ceter punch tools (or one of the deals that is used to pound a nail head into wood so you can finish it) and pad the end so you won't scratch the internals. remove the cooilng head clutch assembly, and pullstart. then using a rubber mallet or hardedned plastic mallet, gently tap the piston to see if you can get it to free up and move to BDC position.

Oh and use a heat gun to heat up the block and sleeve also..
I have to tell you these are your last ditch measures, and will either work, or break something... and cost you a new engine, but from the sounds of it you have a 50 50 chance of needing a new engine anyways.

Also just for future information, when you call for warranty support, give ABSOLUTELY NO information that could even hint at it being your fault. OFNA is notorious for fault finding and using it as a reason to deny you warranty repair services. Granted they make some most excellent budget vehicles IMO, but ther support is lacking to say the least...

romax

Did you heat it to at least 200 degrees F ? Be sure to heat it where the piston & sleeve are. I usually heat straight down on top of the glow plug also making sure it's up to temp on the side of the block. Some people use a hairdryer But it will not get the temp high enough. Yes be sure to remove glow plug & spray penetrating oil down the hole. If you get the engine to turn over be sure to clean out the oil before trying to start engine.

foxfloat

i used the heat gun and i got the piston to move down a little bit and the fly wheel also moved a little bit. but the pull start and the fly wheel is still locked up.

djzachtyler

My Feedback: (4)

I would say that your best bet is to remove the pullstart for now till you free the engine. if you rotate the engine backwards it will cause the pullstart to bind up on itself cause of the one way bearing...

When removing it be careful!!! don't just yank it off or youy could release the spring and jack up the pullstart... What you do is remove the 4 screws, then start to pull the pulstart off, only enough to get a precision flat tip screwdriver in there and under the OWB. then using the screwdriver as a lever pry the whole assembly off slowly...

By doing this you will eliminate the issue of the PS binding up and als allow yourself the ability to turn the flywheel whatever direction you need to to get the piston free...

shankdog626

here's another one, remove the engine from the buggy (if not already done) find a stack of papers
you don't want to get away and use it as a paper weight and just buy a new motor.

Just kidding but all ideas have seemed to be good ones.

But I have one question as to those people that commented on TDC and BDC when shutting it down.
The piston truly never leaves the sleeve so what does it really matter where it is when it cools off?
Does it come down to pushing or pulling the piston in the sleeve when restarting or what?

djzachtyler

My Feedback: (4)

at the top of the sleeve there is a "pinch" where the top is ever so slightly tapered in, not noticeable to the eye but it is there. this is to cause a solid seal so no combutive gasses and fuel can escape during the firing cycle of the combustion. when breaking in the pinch is UBER tight, and will ease after a few heat cycles. the reason for wanting the piston at BDC while cooling is as physics dictate "heat expands, cool contracts" if the piston is TDC on a new mill, and during cooling the sleeve contracts it can seize the piston up. it is good to keep your piston BDC even after break in so you do not lose pinch from the contracting sleeve not being able to contract due to a restriction (the piston)

foxfloat

hey it looks like i need a new piston dose dose anyone know were i can get a new piston or dose anyone have the part number to a new piston

romax

Not sure where you can find parts but if it's like most engines you will have to buy a piston w/ sleeve. It may cost more to repair the engine than it is worth. Hate to break that to you . If that is the case you can buy a better engine for around 150 dollars. Hope you can find the parts for your engine. What's wrong w/ the piston. If it's just scratched a little bit you may be able to run it some. I had a rb engine that the air filter fell off & sucked dirt , scratching piston. I cleaned it put it back together & it ran for 2 gallons. Sorry to be the bearer of bad news.

djzachtyler

My Feedback: (4)

piston and sleeve will run you about half the price of a new engine... you can find a new hyper .21 on ebay fror around 80 bucks.

ShoestringRacer

Foxfloat, why do you think you need a new piston?

What engine does the Hyper 7 come with? The Hyper 21 4 port, or 8 port?



Shankdog, about the piston placement, Djzach answered your question nicely but I'll just add the reason for the taper or pinch in the engine is because the piston does not have a compression ring to seal the chamber, so it needs a pinch seal to seal to keep combustion gasses from escaping. (there are some nitro 2 stroke airplane engines that have a ringed piston as well as most nitro 4 stroke engines have piston ring, but these ABC type car engines all have ringless pistons)

This and general engine operating theory came up in another thread with some extensive discussion. If you have additional interest I would check out the following thread and begin with my post #7. Also read the last post by DarZeelon which is very extensive as well.

http://www.rcuniverse.com/forum/m_8854176/tm.htm

djzachtyler

My Feedback: (4)

thanks for filling in the blanks shoestring! and the Hyper 7 RTRs usually comes with the Hyper .21 3 port, or the Hyper .21 3 port turbo engine. The 7 & 8 port models are "recommended" hop ups...

mp7

just buy an Axial 1S for $110. Comes with new pullstart. It will have more power than any .28 rtr engine except maybe the losi 454.

foxfloat

here's some pics of the piston when i took it apart i found most of the metal from the piston but i think their might still be some in the motor so I'm definitely going to need a new motor. but do you think that I'm entitled to a new motor from ofna. cause this really shouldn't really happen with only running 2 tanks of gas through it idling.

romax

Did you buy it from a local hobby shop or online ? You would have to talk to ofna customer support to see about warranty. It looks like something was on top of piston while it was running & finnaly broke a hole in it. Do you have a picture of the button head ? The piece that bolts on top of the block.

foxfloat

more pics

foxfloat

i bought it from a local hobby shop. and I've called ofna they said theirs only a 30 day warranty and it's been over 30 days. and i'll get a picture of the button head tonight.

foxfloat

pics