Question about pinch

[JessF]

hey guys,

just bought a used engine. The pinch is "good" but I'm not an expert yet. All of my other nitro engines are new, broken in by me, and the pinch is tight. I have yet to run an engine into the ground. So, if I can turn this used engine over by hand with only 3 fingers (i know it's a subjective measure of force) am I looking at weak pinch?

Secondly, at what point can you have a sleeve resized, and should you buy a new piston at the same time?

who does sleeve resizing?

 

[Extreme RC Mods]

It sounds well worn in, when you can start it easy when cool but dies and won't re-start when warm, then it's done or time for a pinch. You use the existing piston as it has been lapped to match the sleeve, send it to rayracing (google it) for $20 but it's also advisable to change the rod and bearings at the same time, they will most likely be worn out as well.

 

[Racer 1966]

Are your 3 fingers on the flywheel or just the crank stub? If just the crank stub,it's probably about done. With the flywheel,it's really hard to say. Does it at least have some resistance(with glow plug in) at tdc? Pinch doesn't help the engine run,that's compression. Pinch is the means for the engine to wear in and achieve good compression. A lot of engines you just have to run to really know.

 

[JessF]

3 fingers on the fly wheel. By the sounds of what you guys are saying, the engine probably has some life left in it.

With my other engine, you can lift the whole truck off the ground with the pull start.

I'll have to see what it's like when I stat it up and run it for a while. $20 US isn't bad to have a sleeve resized. If the engine runs I'll get a chance to see if it's leaking out the front bearing. If the front bearing is leaking I may just cut my losses.

 

[Extreme RC Mods]

The front bearing does not seal the engine, the seal is actually made just behind the front bearing and the induction opening below the carb. The tolerance is tight enough that oil creates the seal between the crank and block. The rubber seal on the bearing is not air tight even when new, they are a light contact seal that is meant to keep dirt out only. The "full contact" "air tight" bearings are not rated for the RPM's and the seal wears very quickly turning them into a light contact seals. Often the front bearing will also leak if the engine is running too rich, there is a little hole behind the front bearing that comes out just below the carb neck that often gets confused as a oil hole to lube the front bearing. In fact this hole is there to suck back oil into the engine that has made it's way past the sealing point between the crank and block. When running rich too much oil can pass through and the hole can not suck it back fast enough causing it to leak, leaning the engine will usually stop this from happening. If you have a leaky front bearing and replacing it solves the problem, what your doing is centering the crank in the block creating equal spacing around the crank which will slow the flow of oil, a worn bearing will let the crank wobble a little which almost forces oil towards the front, replacement will sometimes solve this as long as the crank hasn't worn into the block at which point the leak will always be there.

 

[JessF]

The front bearing does not seal the engine, the seal is actually made just behind the front bearing and the induction opening below the carb. The tolerance is tight enough that oil creates the seal between the crank and block. The rubber seal on the bearing is not air tight even when new, they are a light contact seal that is meant to keep dirt out only. The "full contact" "air tight" bearings are not rated for the RPM's and the seal wears very quickly turning them into a light contact seals. Often the front bearing will also leak if the engine is running too rich, there is a little hole behind the front bearing that comes out just below the carb neck that often gets confused as a oil hole to lube the front bearing. In fact this hole is there to suck back oil into the engine that has made it's way past the sealing point between the crank and block. When running rich too much oil can pass through and the hole can not suck it back fast enough causing it to leak, leaning the engine will usually stop this from happening. If you have a leaky front bearing and replacing it solves the problem, what your doing is centering the crank in the block creating equal spacing around the crank which will slow the flow of oil, a worn bearing will let the crank wobble a little which almost forces oil towards the front, replacement will sometimes solve this as long as the crank hasn't worn into the block at which point the leak will always be there.

hey thanks, very informative. i was under the wrong impression about oil splatter around the front bearing. If leaning out the engine won't fix it, then, and only then, should I consider replacing the bearing.

It's a losi 454 BTW.

if we'd stop getting rain, then snow, then freezing rain and perhaps start with the nice spring weather I may just get out to run it in a month or so.

 

[w bill]

If you take care of your engines properly why don't you just rebuild it then you know what you got no questions then.

 

[Extreme RC Mods]

You can change the front bearing whenever you like, I was just giving some information that I bet a lot of people didn't know either, there seems to be a lot of confusion when it comes to how the front end is actually sealed.

 

[JessF]

If you take care of your engines properly why don't you just rebuild it then you know what you got no questions then.

I've considered that. but when all is said and done I could have bought a new one for the same price. I was looking for a good place to start. If it runs for one season, I've made a wise investment, and I can retool next season. If I buy a used mill, I'd like have to do very little to it to get it running, new exhaust seal, carb seal etc. that's about it.

In the end, buying a used engine is hit or miss, especially when buying online.

 

[w bill]

I've considered that. but when all is said and done I could have bought a new one for the same price. I was looking for a good place to start. If it runs for one season, I've made a wise investment, and I can retool next season. If I buy a used mill, I'd like have to do very little to it to get it running, new exhaust seal, carb seal etc. that's about it.

In the end, buying a used engine is hit or miss, especially when buying online.

I personaly don't like buying used engines or radios it usally ends up costing you more than you save.