O.S 21tm compression issues

Welcome to RCTalk

Come join other RC enthusiasts! You'll be able to discuss, share and private message with other members of our community.

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, and others.

Endeavour

RC Newbie
Messages
8
Reaction score
5
Hi all, this is my first post here, I bought an O.S 21tm two years ago when I was new to the hobby, I bought it to replace the TRX 3.3 in my Revo, I used the heat cycle method to break it in and it is still running great however I've notice that it is fairly easy to spin th flywheel over by hand, I've done every compression test: the liner test where you push the piston up through the sleeve and there was still about a centimetre of space between the top of the piston and the liner, I also cannot spin the engine over with my pinky finger, is my engine on its way out?
 
Hi all, this is my first post here, I bought an O.S 21tm two years ago when I was new to the hobby, I bought it to replace the TRX 3.3 in my Revo, I used the heat cycle method to break it in and it is still running great however I've notice that it is fairly easy to spin th flywheel over by hand, I've done every compression test: the liner test where you push the piston up through the sleeve and there was still about a centimetre of space between the top of the piston and the liner, I also cannot spin the engine over with my pinky finger, is my engine on its way out?

If you didnt run the piston down at the bottom of the block an out of the pinch area of the sleeve on cool down after
each run ,then it is possible!

If that is the case ,you could have the sleeve re pinched .here is the link!

http://www.rayaracing.com/
 
If you didnt run the piston down at the bottom of the block an out of the pinch area of the sleeve on cool down after
each run ,then it is possible!

If that is the case ,you could have the sleeve re pinched .here is the link!

http://www.rayaracing.com/

Thanks for the link!, I will definitely look into it, I always kept the piston at BDC after each run so is possible that the engine is still okay, it runs great, I was also thinking of getting a cheap replacement engine I could bash with while have my 21 rebuilt, any suggestions?
 
Thanks for the link!, I will definitely look into it, I always kept the piston at BDC after each run so is possible that the engine is still okay, it runs great, I was also thinking of getting a cheap replacement engine I could bash with while have my 21 rebuilt, any suggestions?

I think that the sight mentions that ,that it will lose some of its pinch after the piston settles in ,but is normal!
I have a Ofna hyper 21 engine that feels the same way an still runs well ,so you are probably ok!..:thumbs-up:
 
I think that the sight mentions that ,that it will lose some of its pinch after the piston settles in ,but is normal!
I have a Ofna hyper 21 engine that feels the same way an still runs well ,so you are probably ok!..:thumbs-up:

thanks!, I think I'm just paranoid, I'll keep running it and see what happens
 
Run it till it stops running well, then replace the piston and sleeve, or as said get it re-pinched. If it's running ok, I'd leave it alone for now.
 
good idea, I love this engine so much, tons of torque over the 3.3
While it's no true big block, it is a nice improvement over the 3.3.

If you do send to rayaracing, ask for a mild pinch. His non-mild is intended for bump starts and will break pull-starts and likely the ez-start won't touch it. I had him do a few engines for me in the past and even with cheap engines, it lets you get a few more gallons out of them.

If yours is still running fine, not flaming out for no reason or blowing glow plugs for no reason, your likely fine.

I've had a 21Tm in mine for 5 years. I probably only have 3 gallons through it. I don't run nitro nearly as much as I used to, but it's a very reliable engine after the first gallon or so was put through it, it was a bit fussy until then though. Sits for a year, then starts right up and runs perfect every time. I always use ARO in mine and run them completely dry before putting them on the shelf because they will likely sit for a long time.
 
While it's no true big block, it is a nice improvement over the 3.3.

If you do send to rayaracing, ask for a mild pinch. His non-mild is intended for bump starts and will break pull-starts and likely the ez-start won't touch it. I had him do a few engines for me in the past and even with cheap engines, it lets you get a few more gallons out of them.

If yours is still running fine, not flaming out for no reason or blowing glow plugs for no reason, your likely fine.

I've had a 21Tm in mine for 5 years. I probably only have 3 gallons through it. I don't run nitro nearly as much as I used to, but it's a very reliable engine after the first gallon or so was put through it, it was a bit fussy until then though. Sits for a year, then starts right up and runs perfect every time. I always use ARO in mine and run them completely dry before putting them on the shelf because they will likely sit for a long time.

Thanks for the heads up in regards to the pinch level, it's not flaming out or blowing glow plugs at all, it's got about 2 gallons through it and its really starting to wake up, I also wanted to say I saw your review a few years ago on the 21tm and it was one of the reasons I got one, would you recommend getting a new sleeve and piston for it when it goes or should I just buy a cheaper engine?
 
Compression and pinch are two different things. An engine has to have compression to run not pinch. Pinch is a mechanical interference between the piston and cylinder and is used the allow an engine to slightly wear-fit together to achieve compression. It's used because it's a cheaper/easier way to make the engine without having to make and install rings on the pistons. Some motors will retain some pinch in the cylinder while others will wear just right to maintain compression. Both usually feel the same with glow plug in but with it out, some will still have resistance when reaching TDC.

I personally say the only real test of the engine condition is how it runs and tunes. As long as it runs and tunes good, it's good.
 
Thanks for the heads up in regards to the pinch level, it's not flaming out or blowing glow plugs at all, it's got about 2 gallons through it and its really starting to wake up, I also wanted to say I saw your review a few years ago on the 21tm and it was one of the reasons I got one, would you recommend getting a new sleeve and piston for it when it goes or should I just buy a cheaper engine?
Odds are, if you take care of it and put the piston at BDC any time it's not running, it should last you many more gallons before it starts getting blow-by and having flameouts, loss of power. Once you have run the 21TM, you will likely not be content with anything less, so at the very least, I'd get the one you have pinched. With the lack of NewEra big block mounts, it kind of limits you on your options for something stronger. That's what I have in my BB revo with an LRP28 in it as well as a THS BB rear pipe that I modified the header to work with.

Even the cheaper OS engines I've had many years ago would get 8-10 gallons through them. I've had a few OS21RG's that lasted that long before I had them pinched. I have a 18TM that probably has that many gallons through it and it still runs like a top. That's what I had in my BB revo before I put a BB in it.
 
Odds are, if you take care of it and put the piston at BDC any time it's not running, it should last you many more gallons before it starts getting blow-by and having flameouts, loss of power. Once you have run the 21TM, you will likely not be content with anything less, so at the very least, I'd get the one you have pinched. With the lack of NewEra big block mounts, it kind of limits you on your options for something stronger. That's what I have in my BB revo with an LRP28 in it as well as a THS BB rear pipe that I modified the header to work with.

Even the cheaper OS engines I've had many years ago would get 8-10 gallons through them. I've had a few OS21RG's that lasted that long before I had them pinched. I have a 18TM that probably has that many gallons through it and it still runs like a top. That's what I had in my BB revo before I put a BB in it.


++:thumbs-up:
 
Back
Top