Im new to the world of nitro, iv always run electric, had a HPI Rush roller laying around for ages and finally got round to rebuilding it, which i finished today. heres the problem part-

After finally getting the engine running i noticed it was getting pretty messy (fuel everywhere) so i stopped it.. i then realised the problem.. as i pulled the pullstarter slowly and looked closely fuel was leaking out between the engine block and cooling head, i removed the head, cleaned up the mess and put the glow plug back in place then screwed the cooling head back in in the proper way (top left screw, bottom right and so on so the preassure was equal) now iv dont this no leakes but the pressure seems too much, its hard to make the engine turn, like the pressure is too much for it to turn propperly.. if i loosen the cooling head it turns fine but then ofcourse there would be a gap again.. what do i do?

That is the pinch on a regular ABC engine. Some engines are really tight.

You can put another gasket on the glowplug to reduce compression a bit and heat the engine with a heat gun prior to running. After a few tanks the engine will be run-in and you won't feel such a tight pinch.

its not a new engine so its already been run in

Take the plug out and then see if it will turn over. If so, then it is just is a high compression engine. If not, either you left out a head shim causing the piston to hit something, or the screws were not tightenbed equally cocking the cylinder and jamming the piston.

Quote:

ORIGINAL: Patxipt

You can put another gasket on the glow-plug to reduce compression a bit and heat the engine with a heat gun prior to running. After a few tanks the engine will be broken-in and you won't feel such a tight pinch.

Pat,


Adding a plug gasket to the one already there, will reduce the compression by very little...
The effect may be a reduction of the outward expansion of the sleeve, as a result of compression, possibly making the TDC pinch even tighter...

However, it will also reduce the engagement ('bite') of the glow-plug's thread in the head's thread, by about one complete turn.

This may not actually cause direct damage. But if you tighten the glow-plug to the same degree as you did before, it will potentially pull the remaining threads out of the plug's bore... It may even allow the plug to 'shoot' out of the head, while the engine is under full-throttle...

This may require Clarence F. Lee's help; installing a Heli-Coil. Or it may require a new head...


I would consider doing this, a negative advice.

Also, break-in does reduce the pinch somewhat, but a good measure should remain, since the differential heating of the sleeve is 'a feature' of all tapered-bore engines; not just of new ones. It should never be too loose.

More than likely you've simply fixed the compression leak and now it's as it should be but to ease your mind I agree with what spaceworm said. Take the plug out and see how it feels. I'm presuming it's a pull start car engine and these can feel hard to spin over because of the very small leverage acting directly on the crankpin. It's not a pinch problem because you can spin it over easily when there's a compression leak. One trick some people do is to loosen the plug just a little to give a small compression leak then, once it's running, tighten the plug but I don't really recommend this.

And sorry Dar, but that bit about an extra plug washer and reducing outward expansion of the sleeve because of less compression......well, what can I say ?

Nothing should be loose, Arkz, because something will break sooner or later.

You could easily try reducing the nitromethane percentage and reducing the glow plug heat range.

If your engine has high compression and improper cooling and/or lubrication, it may be suffering pre-ignition (an advanced ignition point).
That pre-ignition interferes with the proper functioning, making it look like the pressure is too much, when it is just the right pressure but happening too soon (before the piston reaches the top position).

Read this article:

http://www.flyrc.com/articles/tune_your_engine_1.html

Welcome to the forums!

ArkZ,

The compression your experiencing is very desirable. If you are new to nitros, it will take some time to learn about them.

However, there's an easy way to start these. I don't know what kind of glowstarter you have. There's a company out there call Sonic Tronics that makes a "McDaniel Ni-Starter"
The bottom of this igniter that goes onto your glow flug is hex shaped, like a socket. You can use this glow starter to loosen the plug a 1/2 to 1 turn while you're starting it.

I imagine you're yanking the cord, and it's kicking and probably pissing you off. Loosen the plug, it will relieve compression, but it will start. Once it's running, use your Ni-Starter to firmly tighten it down. Do it somewhat quickly, as the more time you wait, the more fuel and gasses will leak through the threads making a mess of the head.

If you don't have a McDaniel igniter....then you can use a 4 way wrench before and after you start it. It's just another step and another thing to grab while you try and fire it up.

Once the engine is broken in, and you're accustomed to how much you need to "prime" this engine for cold starts, you won't need to trick of loosening the plug. It's easy to over prime these, and get too much fuel in the case, and have trouble pulling the string, kicking back, etc.

Run this thing rich until it's broken in. When you're driving it around, you want to see a nice belch of smoke when you advance the throttle.

That has to be the first time I've ever heard someone be advised to loosen a glow plug to make the engine turn over easier. I'm curious what having all that combustion pressure bearing on the loose plug does to the threads. Nothing good I'm sure.

If you can't crank the engine over as it is, then use a heat gun to warm the head before you start it. If you can crank it over and it's just difficult, then don't worry because you don't have a problem.

A loose glow plug will loosen on up and blow out.

A friend has a OS 160 and his loose plug didn't blow out. But it got so hot that the Silver OS #8 plug turned blue-black.

Quote:

ORIGINAL: downunder

...Take the plug out and see how it feels. I'm presuming it's a pull start car engine and these can feel hard to spin over because of the very small leverage acting directly on the crank-pin. It's not a pinch problem because you can spin it over easily when there's a compression leak. One trick some people do is to loosen the plug just a little to give a small compression leak then, once it's running, tighten the plug but I don't really recommend this.

Sorry, Brian, but if as you wrote, you don't really recommend this; then why did you bother write it?

From reading subsequent posts, it seems no-one recommends this.


I remember an old cement mixer, powered by a single-cylinder Diesel, that had a special technique for starting.

It had a heavy flywheel and a decompression valve.
Decompressed, it was spun to a respectable RPM with a hand-crank, then the decompression was undone...

The engine started immediately every time.

That's hot

Loosening the glow plug to start a high compression inboard boat engine was common once. In fact there were companies selling special long reach ni starters using a nut driver specifically to loosen the plug and engerize it and then start the engine and then tighten the plug back up. It may been have because the inboard boat engines had to be started with a belt around their flywheel which made it hard to start them. But I knew someone with a Mazda GLC that blew out (stripped) all of its fouir plugs when the engine was started and driven before the plugs were tightened down fully; gas blowby may have contributed to erosion of the threads and the plugs blowing out. The GLC engine had the plug threads trapped directly into the aluminum heads, not unlike some of our glow engines

The loose glow plug trick works, I had to do this occasionally when I was running a pull start on my RC10GT, but was only needed when the engine became flooded. Try tightening the plug and turning it over without any fuel, but make sure the engine and tank are completely drained.

High compression motor cycle engines which employ a kick start, as well as high compression snowmobile motors which emply a pull start, also use decompression valves much like the cement mixer motor Dar remembers.


Granted, these are built for that specific purpose. Glow plugs, on the other hand weren't designed for this, but can be used for this purpose. It's not a bad idea for someone who's new and doesn't have a good feel for how to prime...or flood...their engine. Once there's a familiarity with starting the motor, it won't be necessary to relieve any compression.

In the meatime, for someone who's just starting..it sure is a lot easier, and a lot less discouraging than breaking pull cords, and fighting the thing like crazy with the thing when there's a little too much fuel in the case. I've heard dozens of folks new to nitro have a lot of trouble with this...it's more enjoyable when you can get the thing started and run a little bit...then learn to tune it..which is another learning curve in itself.

iv managed to get it running, seems to be ok now except quite a bit of unspent fuel seems to be coming out of the exhaust, and when i try and rev it be it sudden or gentle it seems to take a few seconds before it will actually rev up.. any advice?

It is getting too much fuel.

Turn the needle valve in a little

rightyho, so the needle valve limits how much fuel it gets? what about the screw i can adjust where the fuel pipe connects? i thought that would let me modify more air/more fuel but if the needle valve does that.. damn its so simple with electronics lol

The screw down inside the tube where the fuel goes in is the needle valve

http://www3.towerhobbies.com/cgi-bin...LXPZG9&P=Z

Ah ok, what's the other one then? on the side of the carb, if i take the air filter off i can see it and if i adjust it it moves in and out towards a point in the middle

The screw on the front of the carburetor has noting to do with the mixture. It is just to adjust the minimum closed position of the throttle. (Idle speed)

Typically this screw is adjusted out of the way of the throttle and your throttle position is adjusted by the radio servo

That sounds like you are describing the low speed mixture needle. If there is a screw slot in in a recessed area in the center of the carb's throttle arm, then it's prob. the low speed adj. screw/needle.

That adjustment, if too rich, will contribute to the difficulties you describe.

Can you post a picture?

Edit: Yeah...it's hard to tell just exactly which screw you might be talking about? One might be the idle speed stop screw...the other, if it's in the center of the carbs throttle arm (where the servo's pushrod attaches ) then it's the low speed mixture.

i didnt mean that, the idle one is a little black screw next to the throttle with a spring on it in the case of this carb, when i adjust it it limits how low the throttle goes, but theres another bigger screw that has a needle on the end when i look down the air hole... could this be a high speed needle?

Which engine do you have?

HPIT-15