R/C Tech Forums

Go Back   R/C Tech Forums > General Forums > Nitro Off-Road

Reply
 
Thread Tools Search this Thread
Old 04-09-2009, 09:25 AM   #16
Tech Regular
 
markr04's Avatar
 
Join Date: Jan 2009
Location: TX
Posts: 421
Trader Rating: 1 (100%+)
Default

Quote:
Originally Posted by H4CK3D4L1F3 View Post
Okay so with a little searching i found out what pinch is and it sounds pretty plausible. Do i have to take it in somewhere to get it pinched or is this something i can do at home?
You need specialized tools to pinch a sleeve and they're expensive. You can send it off to a guy on this forum and he'll do it for $15 (I don't remember his name, it's just something I've seen in his forum sig). There are other people also on this forum that you can send it off to.

One of my local hobby shops has a modding and pinching service - they have the good tools for it. It's $20 there. Maybe call your local hobby shop and ask if they can do it.
__________________
Xray 808 2010 Spec - O.S. V-Spec Speed - Airtronics M11-DSSS
Losi 8ight-T 2.0 - RB Killer 9 - Airtronics M11-FHSS-2
Losi XXX-CR - Tekin RS / Novak Ballistic 13.5 - Airtronics M11-FHSS-2
markr04 is offline   Reply With Quote
Old 04-09-2009, 09:29 AM   #17
Tech Adept
 
Join Date: May 2008
Posts: 223
Default

Quote:
Originally Posted by Jasonguy View Post
At lower RPMs the engine has more time to charge and discharge the cylinder and it is under less demand. At higher RPM the leakage by the piston is too great and creates a premature exhaust port. In a multi cylinder engine this would be indicated by a skip or dead miss in the powerband.
I am not disagreeing with you, because honestly I am not qualified to comment, however wouldn't an engine create more compression the higher the rpm was? If that piston is moving faster and faster wouldn't there be LESS time for air to escape, building MORE pressure (compression)? Assuming the leak is the same size at low rpm vs high rpm, trying to move a fluid (air) through it faster would create more psi. (I would think)

Again, I am anticipating you have great evidence/explanations to argue me wrong. I am just trying to learn something.
Larks is offline   Reply With Quote
Old 04-09-2009, 09:31 AM   #18
Tech Regular
 
markr04's Avatar
 
Join Date: Jan 2009
Location: TX
Posts: 421
Trader Rating: 1 (100%+)
Default

Quote:
Originally Posted by H4CK3D4L1F3 View Post
Another thing is, is that it happens at the same rpm everytime. It's very very consistant. There's no variation when it dies.

Im not sure if this is relevant or not. im just throwing it out there.
I didn't see anything saying you tried to richen it more. Try that if you haven't already.

Also, with the engine cold, turn the flywheel to see if it's hard to turn past TDC (Top Dead Center). Try doing this with the glow plug out of the engine. With the glow plug out, you're feeling only pinch and that's the better test. When it's in place, you're feeling pinch + whatever compression it may have and that's not the better test.
__________________
Xray 808 2010 Spec - O.S. V-Spec Speed - Airtronics M11-DSSS
Losi 8ight-T 2.0 - RB Killer 9 - Airtronics M11-FHSS-2
Losi XXX-CR - Tekin RS / Novak Ballistic 13.5 - Airtronics M11-FHSS-2
markr04 is offline   Reply With Quote
Old 04-09-2009, 09:35 AM   #19
Tech Adept
 
Join Date: May 2008
Posts: 223
Default

Quote:
Originally Posted by markr04 View Post
I didn't see anything saying you tried to richen it more. Try that if you haven't already.

Also, with the engine cold, turn the flywheel to see if it's hard to turn past TDC (Top Dead Center). Try doing this with the glow plug out of the engine. With the glow plug out, you're feeling only pinch and that's the better test. When it's in place, you're feeling pinch + whatever compression it may have and that's not the better test.
How much 'pinch' should you feel on a good engine? I have wondered this for awhile because I have noticed that mine doesn't have much resistance to turning the flywheel without a glow plug in. You can feel it get just a bit snug but nothing like the amount of compression you feel when the plug is in place.
Larks is offline   Reply With Quote
Old 04-09-2009, 09:38 AM   #20
Tech Rookie
 
Join Date: Apr 2009
Posts: 12
Default

Quote:
Originally Posted by markr04 View Post
I didn't see anything saying you tried to richen it more. Try that if you haven't already.

Also, with the engine cold, turn the flywheel to see if it's hard to turn past TDC (Top Dead Center). Try doing this with the glow plug out of the engine. With the glow plug out, you're feeling only pinch and that's the better test. When it's in place, you're feeling pinch + whatever compression it may have and that's not the better test.
I tryed richening it and leaning of out. It made a difference but it still died at high rpm
H4CK3D4L1F3 is offline   Reply With Quote
Old 04-09-2009, 09:41 AM   #21
Tech Adept
 
Join Date: May 2008
Posts: 223
Default

Quote:
Originally Posted by H4CK3D4L1F3 View Post
I tryed richening it and leaning of out. It made a difference but it still died at high rpm
It sounds like you have tried this, but I was having very similar problems and had changed my glow plug twice. I tried just about everything else then discovered that I had a bad batch (as in about 6 consecutive) of RB plugs. I finally got to some better plugs and haven't had the trouble since. I have since determined that turbo plugs are kind of finicky and I always doubt them first.
Larks is offline   Reply With Quote
Old 04-09-2009, 09:57 AM   #22
Tech Regular
 
markr04's Avatar
 
Join Date: Jan 2009
Location: TX
Posts: 421
Trader Rating: 1 (100%+)
Default

Quote:
Originally Posted by Larks View Post
How much 'pinch' should you feel on a good engine? I have wondered this for awhile because I have noticed that mine doesn't have much resistance to turning the flywheel without a glow plug in. You can feel it get just a bit snug but nothing like the amount of compression you feel when the plug is in place.
An amount of acceptable pinch is hard to describe in text. But what I think from your description:

Your pinch is pretty much gone. Considering that, the compression you described with the plug in place is gone when the engine is hot.

When your engine heats up, the sleeve expands. The pinch is kind of a preemptive measure which makes a cold engine hard to turn, but when hot (running temp) the expanded sleeve offers good compression. When your pinch is gone, the sleeve expands beyond the circumference of the piston and you lose compression.

I'm not a pro, though.
__________________
Xray 808 2010 Spec - O.S. V-Spec Speed - Airtronics M11-DSSS
Losi 8ight-T 2.0 - RB Killer 9 - Airtronics M11-FHSS-2
Losi XXX-CR - Tekin RS / Novak Ballistic 13.5 - Airtronics M11-FHSS-2
markr04 is offline   Reply With Quote
Old 04-09-2009, 10:03 AM   #23
Tech Adept
 
Join Date: May 2008
Posts: 223
Default

Quote:
Originally Posted by markr04 View Post
An amount of acceptable pinch is hard to describe in text. But what I think from your description:

Your pinch is pretty much gone. Considering that, the compression you described with the plug in place is gone when the engine is hot.

When your engine heats up, the sleeve expands. The pinch is kind of a preemptive measure which makes a cold engine hard to turn, but when hot (running temp) the expanded sleeve offers good compression. When your pinch is gone, the sleeve expands beyond the circumference of the piston and you lose compression.

I'm not a pro, though.
But in your opinion, being that it seems I still have good compression (no serious air leaks) this would be a good engine to either replace the pis/sleeve or get a pinch?
Larks is offline   Reply With Quote
Old 04-09-2009, 11:00 AM   #24
Tech Regular
 
markr04's Avatar
 
Join Date: Jan 2009
Location: TX
Posts: 421
Trader Rating: 1 (100%+)
Default

Quote:
Originally Posted by Larks View Post
But in your opinion, being that it seems I still have good compression (no serious air leaks) this would be a good engine to either replace the pis/sleeve or get a pinch?
A pinch can give you another 6-10 gallons, from what I understand, and it should run almost like new (assuming the other components are good). And you can have a sleeve re-pinched once or twice. After that, get a piston/sleeve (and probably rod and bearings, too).

Eventually other parts will fail... crank, carb, case. But until then, you can theoretically keep an engine going for a long time with pinches and piston/sleeve/rod replacement.
__________________
Xray 808 2010 Spec - O.S. V-Spec Speed - Airtronics M11-DSSS
Losi 8ight-T 2.0 - RB Killer 9 - Airtronics M11-FHSS-2
Losi XXX-CR - Tekin RS / Novak Ballistic 13.5 - Airtronics M11-FHSS-2
markr04 is offline   Reply With Quote
Old 04-09-2009, 11:11 AM   #25
Tech Elite
 
Join Date: Mar 2009
Location: Aurora, Colorado
Posts: 3,644
Default

Quote:
Originally Posted by markr04 View Post
A pinch can give you another 6-10 gallons, from what I understand, and it should run almost like new (assuming the other components are good). And you can have a sleeve re-pinched once or twice. After that, get a piston/sleeve (and probably rod and bearings, too).

Eventually other parts will fail... crank, carb, case. But until then, you can theoretically keep an engine going for a long time with pinches and piston/sleeve/rod replacement.
depends on the quality of the sleeve - and how hard you run it. for me and my OS engines - a pinch will only last maybe two days of racing.

I would strongly suggest just buying a new motor or at very lease a new piston and sleve - if you going to go that far break in the new piston and sleve with you old conrod and after it is broken in - replace it with a new conrod.

but IMO - just get a new motor
__________________
TLR - Spektrum - Horizon - TLR 8ight 4.0 - TLR 8ight-T 4.0 - TLR 22 4.0 - Orion
token is offline   Reply With Quote
Old 04-09-2009, 12:08 PM   #26
Tech Rookie
 
Join Date: Apr 2009
Posts: 12
Default

Does anybody know the details on traxxas motor exchange program. I read on their website but I wasn't sure If you have to purchase the warrenty at the time you buy your car or is just $90 no matter what?

Anybody tried this?
H4CK3D4L1F3 is offline   Reply With Quote
Old 04-09-2009, 12:15 PM   #27
Tech Rookie
 
Join Date: Apr 2009
Posts: 12
Default

Quote:
Originally Posted by Larks View Post
It sounds like you have tried this, but I was having very similar problems and had changed my glow plug twice. I tried just about everything else then discovered that I had a bad batch (as in about 6 consecutive) of RB plugs. I finally got to some better plugs and haven't had the trouble since. I have since determined that turbo plugs are kind of finicky and I always doubt them first.
So your car was doing the same thing? That's reassuring. I'm going to try new plugs when I get home from work.
H4CK3D4L1F3 is offline   Reply With Quote
Old 04-09-2009, 12:45 PM   #28
Tech Adept
 
Join Date: May 2008
Posts: 223
Default

Just some background, the motor is an RB concepts c6 BB l2g. It is about 7 months old and has only about 1.5 gallons through it. I broke it in properly and it gives great power. It did overheat once, I temped it coming off of the track (out of gas) at about 285F (normally it runs at a consistent 240F). I quickly put it BDC and didn't have any noticeable problems until it started dying at high rpm (after it got up to temp). I went through different tuning/air leak checks and finally determined (thanks to Houston on these forums) that I had not only a bad plug, but about 6 bad plugs in a row. I changed to an O'donnel t plug and it runs great now. I will say that when reading the concern about noticing pinch without a plug in the head I have noticed there is very little. This was my interest in the comment. I am kind of a "not broke, don't fix it" guy, but I was trying to learn something as well.
Larks is offline   Reply With Quote
Old 04-09-2009, 02:46 PM   #29
Tech Initiate
R/C Tech Elite Subscriber
 
Join Date: Feb 2009
Posts: 44
Trader Rating: 4 (100%+)
Default

Quote:
Originally Posted by Larks View Post
I am not disagreeing with you, because honestly I am not qualified to comment, however wouldn't an engine create more compression the higher the rpm was? If that piston is moving faster and faster wouldn't there be LESS time for air to escape, building MORE pressure (compression)? Assuming the leak is the same size at low rpm vs high rpm, trying to move a fluid (air) through it faster would create more psi. (I would think)

Again, I am anticipating you have great evidence/explanations to argue me wrong. I am just trying to learn something.
Again, I am anticipating you have great evidence/explanations to argue me wrong. I am just trying to learn something.[/QUOTE]


Well in one of these engines the compression ratio is ideally pretty constant. it is determined by cylinder bore, piston stroke,and the volume of the combustion chamber. Engine wear is the only thing that really changes it. The effect that was suggested is due to you losing an acceptable seal between the piston and the sleeve it in-effect changes the volume of the combustion chamber when that happens.

When this happens as your engine revs up and begins to take in more and more fuel and air. It will reach a point that as the piston trys to compress the mixture it will simply squeeze too much air by the piston and cause it to go rich and die. Once you reach that point it will do it consistantly at that rpm.
Jasonguy is offline   Reply With Quote
Reply

Similar Threads
Thread Thread Starter Forum Replies Last Post
"the tuning bible" houston Onroad Nitro Engine Zone 311 04-24-2017 11:18 PM
Team Orion CRF Wasp Rev X-Dyno results Nano Onroad Nitro Engine Zone 1531 11-07-2010 01:43 AM
Yay Dvx400Rider Nitro Off-Road 7 02-27-2009 08:25 PM
Please Help Muah! Speedjunkyz Nitro On-Road 36 09-05-2008 07:13 AM



Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are Off



All times are GMT -7. It is currently 05:08 PM.


Powered By: vBulletin v3.9.2.1
Privacy Policy | Terms of Use | Advertise Content © 2001-2011 RCTech.net