Symptoms of a used up nitro engine??

[Mickstix]

What are some symptoms of a used up engine? I've got an .18 SH in an 1/10 4x4 buggy, and it ran fine for a gallon of fuel, but then started dieing randomly when I'd let off the throttle. (this was when it was tuned near perfect, as far as I could tell).. There's other stuff goin on too, but I'd like to hear what some symtoms are of a worn out motor. (then I'll give a detailed report of what mines doing) Thanks!

 

[Racer 1966]

The main symptoms are :

Very low compression - you can easily turn the flywheel a complete revolution with little resistance

Hard starting - will usually start cold but nearly impossible when hot.

Randomly dies not tracable to other problems.

 

[Mickstix]

Crap, that sounds awefully familiar.. :\ Thanks for the info!! As I said, mine started shutting off for no apparent reason, then it wouldnt start at all so I rebuilt (ie: cleaned) the carb and needles and put everything back to stock settings. It fired right up then, but was hard to tune, and once I got it tuned again it started with the random shut offs again, mainly as soon as I'd come off the throttle.. And it wouldnt idle at normal rpms.. I had to turn up the idle to where it almost moves on its own.. And, after it shuts off I have to pull my arm off to get it refired, if it'll refire at all.. It'll be tryin to start, but wont.. I did the air leak test, fuel system leak test, new plug, etc.. I'm gonna pull the motor and tear it down and see what I can see.. I'm sure the culprit is gonna be sand that came in through the aircleaner.. (It used to fall off all the time, under the body so I couldnt tell) and here in Fl. there's sand everywhere, especuially in the sand traps I drive through on the golf course.. DOH!!! Too bad I didnt even get a full gallon through the thing.. And its a shame I didnt fix the air filter problem when it first happened.. Being new to nitro I just didnt take the risk as seriously as I should have.. Live and learn.. Oh well, I'm rambling AGAIN... Thanks again for your help!

 

[MotoGod]

If you still have compression, you may want to check for air leaks on the engine. An air leak will throw off your tune in a hurry, and make it run very erratic. Typical sign of low compression/no compression is the motor will die when it reaches operating temp and the sleeve expands a little.

If you can pull it apart see how far up into the sleeve you can push the piston when it's out of the engine. If you can make it within 1/6th - 1/8th of an inch to the top or less....it's probably too worn to run properly. If the piston gets no where near the top of the sleeve easily...then the pinch is probably OK still. When I tore down my LRP I could push the piston all the way to the top and the piston crown was above the upper portion of the sleeve. No pinch left....and hence my flameout problems when it got warm.

Nitro is fun ain't it? hehe

 

[Mickstix]

I'll take some pix when I get it pulled apart and see how the piston fits the sleeve.. Thanks for the info! ANd yea, nitro is tooo much fun, especially when they aint running properly..

 

[Mickstix]

Well, it seems to have a little pinch left? The compression isnt the best though.. I dunno, I'm still going to seal it back up and see what happens before making any decisions.. If it's still a mess I'm go the "motor exchange" route, and get a new one for like 50-55$ But here's the pix I promised.. What do you think? 1st image is where the piston first feels resistance, and the 2nd is how far I could push it in w/o useing excess force.. Thanks for your help!

 

[olds97_lss]

Also, you may want to give your clutch and cb bearings a look. If they are dragging, it makes an engine not want to idle as well.

Considering how bad mine looked prior to getting them pinched, I'd say you may want to check for air leaks or a dragging clutch issue. When I had mine pinched, they gave some of the symptoms yours did, but the pinch was way worse.

You can see mine here pre and post pinch:
https://www.rcnitrotalk.com/forum/showthread.php?t=56420&highlight=pinch

The only one that had weird tuning issues and the pinch wasn't that bad was the XTM. Once it was re-pinched, it ran a lot better. The other two engines though ran better than the XTM did prior to pinching!

 

[Mickstix]

Clutch checked out ok.. What are the CB bearings? Any idea how to remove a crankshaft from one of these engines? Are they pressed in or something? I can't see any obvious nuts or pins or anything holding it in? (I'm not planning on removing it, just wondering for curiosity sake) Thanks! (Note we posted at the same time before.. Did you see the pix I posted of the piston/sleeve? opinions?) Thanks again!!

 

[olds97_lss]

Yeah, that's why I added the link to my P/S pinch thread. While yours isn't "great", it's not real bad though either. I would maybe seal the engine up with RTV and check the tank/lines for holes and try it again.

To take the crank out, you take the sleeve out, piston/con-rod, then just gently whack the tip of the crank on a block of wood and it should pop loose and go up in the engine.

To get the bearings out, take everything off/out of the crank case. Carb, back plate, piston/sleeve/con-rod, crankshaft. Then you heat the engine in the oven up to around 250F, then whack the back down flat on a piece of wood and the front near the carb hole on the wood to get the front one to pop out. Works like a charm.

 

[Mickstix]

Thanks for the link and crank/bb removal tips!! Yea, mine resembles your XTM pre pinch.. I'm going to reseal it and see how she does.. Only thing now is, I dont have an exhaust manifold gasket? Tore up the original when I took the manifold off.. Do I need to find a new gasket, or can I get away with using the "Ultra Copper" RTV silicone only?? Thanks again for the info and help!!

 

[MotoGod]

Like olds said...your pinch isn't great, but it should be plenty to keep on running for another gallon or so I'm sure..maybe even longer. Seal it up tight and see what it does. He's given you the info ya need on that topic.

As far as gaskets go....I'm sure you could use some RTV, but the gaskets are like $2 for a 2 pack typically at your LHS. I would just go get some to make sure you get a nice seal out of it.

 

[Mickstix]

Thanks! I didnt even think about the lhs for a gasket. I guess alot of these motors have similar exhaust manifolds? Cause I'm sure they dont carry anything for Redcat or SH.. But I'll definitley check and see!

 

[ohsnap]

Most rear exhaust engines of a similar size can share exhaust gaskets with no sealing issues. The gaskets are usually sized small block or big block - depends upon the size of your exhaust port. Not sure where the SH .18 fits in the scheme of things. Picco being an exception as their exhaust port is smaller than average - so you sometimes have to play around to get theirs to seal.


Ofna makes two sizes of affordable bearing pullers.
http://www.ofna.com/images/parts-images/10797.jpg
http://www.ofna.com/images/parts-images/10798.jpg

I used to use a 1/4 inch Dasco Pro punch to push (hammer) out the front bearings and the method works well. The punch is small enough to fit through the center of most front bearings and then it's taper catches the bearing so that you can push it out without damaging anything.
I never figured out how to remove the rear bearing, so I finally broke down an bought the Ofna kits.

 

[Mickstix]

Those are some nice looking tools!! Definitely be nice to have, but probably out of my price range for just tinkering with the one or two motors I have.. On a side note, I was able to get new exhaust gaskets (For my SH .18) from my LSH.. They were an "Associated" part, made for "side exhaust" engines.. Got 3 of em' for $2.00 Now I just need it to warm up a little around here and I'll find out what I've got left in this engine.. Unfortunately it's lookin like next Tues or Wed will the 1st day it gets to the 50* mark... Dang cold for Central Fl.!!! Callin for flurries in the morning.. Yikees!!

 

[ohsnap]

Pushing out the front bearing using a punch always worked and I didn't break down for years until I needed to replace a rear (internal) bearing.
Each OFNA kit runs about fifty bucks.
Besides pulling out the bearing, the tool also helps when you go to install one too.

My previous comments on exhaust gaskets - I assumed that your .18 was rear exhaust. Ignore my comments concerning the Picco. Glad you found what you needed.

 

[Mickstix]

As promised, I'm here with my report.. I ran it yesterday.. Fired right up, idled fine, bogged a little off the line.. (needed tuning) Once warm, I got it tuned up and did one full pull down the driveway and it cut off.. Pulled and pulled and finally got it restarted, did another pass and it shut off again.. Pulled until my arm fell off and it wouldnt start again. So, it's officially toast.. Let this be a reminder to any newbies who just get into nitro.. Make darn sure the aircleaner is properly secured to the carb, and if you happen to notice it has falled off, stop the motor immediately!! When the buggy was new, I'd be running it on a golf course here in FL, and the aircleaner would fall off (under the body w.o me knowing) and I would keep running it until it was out of fuel.. It did this probablay 3 or 4 times before I finally got the aircleaner attached properly, so it'd stay on in a rollover.. Anyway, it was run through the sand traps and obviously ingested some sand and as a result, the pinch is gone with not even a full gallon of fuel run through it.. So, be careful in sand or harsh environments, keep your air filter clean and oiled properly, and again make sure the aircleaner housing is properly secured to the carb!!