08-30-2005, 12:20 AM
Here's a great article on how to mod the 2.5r. I'm going to try it cuz I think it's a good idea to have a spare motor with less power than a TZ for loose/tight tracks. Check it out:
Introduction
The TRX 2.5 is a well designed powerplant that doesn't need much porting to develop phenominal power, in fact it does quite well without any added port work. Being the Power Hungry folk that we are there is always a desire to try to pull more ponies out of our powerplants and that's where your trusty dusty dremel comes into play. Along with a steady hand and a ton of patience . I figure pictures are worth a thousand words so for the most part I will let them speak for themselves.
Bits I used to do this Job
http://www.rcpics.net/view_single.php?medid=10748
Before disassembling your mill, make sure that the engines exterior is completely free of debris. You can do this by blowing it off with compressed air and spraying it down with denatured alchohol. I also like to use a toothbrush to get the crust off and follow it all up with another blast of compressed air. When you are confident that no grit or sand will make it into your case and perhaps your bearings when breaking down your engine you are free to proceed. I remove the clutch assembly and the nut and flywheel first, followed by the head backlate and finally the carb.
I always look into the carb case bore after removing the carb to see if the crank window matches up flush with the carb case bore on the front and rear edges (not side to side). I also look for scratches on the crankshaft that wrap around the crank, clear signals that Dirt or debris has entered through the air filter. Look at the base of the carb, is the throat lip thickness equal to the matching lip inside the case? If not you will have to match these two surfaces either by coning the inside diameter of the carb bore or grinding away some material from the case bore. In the TRX 2.5 you have to do neither, the stock 2.5 carb is already portmatched to the case and needs no work whatsoever. The carb inlet is also tapered and requires no work, a welcome sight!
Next peer into the Exhaust port... Does the sleeve port line up perfectly with the case exhaust port? Do you see any Brass sleeve showing? On the TRX 2.5 this is also portmatched and needs no work. Now remove the sleeve rod and piston, followed by the crankshaft.
Time to remove the bearings from the case, this can be a real pain on stubborn engines! You will need to bake the engine in the Oven or toaster oven... Most recommend 350degrees for ten minutes, I find that they don't release at this temp most of the time. I just set my oven on the maximum setting and wait about five minutes. Pull the engine out wearing your oven mitt or pot holder and rap the engine on the countertop backplate down until the inner bearing drops out, if it won't budge heat it again for a few more minutes. After removing the inner bearing, turn the engine over insert the crank into the front bearing and give it a wiggle as you slide the bearing out of the case. Let all parts cool to room temp, bag your bearings in a ziplock bag to keep them free from particle contamination. Now you are ready to get down to business!
WARNING: Before you work on the crankshaft put a small peice of fuel tubing onto the rod Journal to protect it's surface from accidental slips with your tool!
I always start on the crankshaft. The TRX 2.5 crank is probably the only part that holds back the 2.5 from achieving maximum RPM and power. You will notice that the bore is very small but has a nice slope at the induction window. We want to bore out the crank considerably(bits 2+1 then 6+7), When I'm done boreing out the crank port, I usually knife edge the inside of the induction window on the crank that sits below the carb(bits 5+, you can see that on the 2.5 there is alot of material to remove, try to keep the integrity of the slope into the crank bore so the mixture enters as smooth as possible!
http://www.rcpics.net/view_single.php?medid=10750
Typically, I will then chamfer the area leading out into the crankcase (bits 4+7) before finally adding the scallop to the left side of the opening(bits 3+7)...
http://www.rcpics.net/view_single.php?medid=10749
If you choose to, you can follow up all your cuts with a polishing bit (like bit 9) and some metal polish such as Mothers or the ilk.
Next I do the sleeve, remember the order is up to you. Make sure you make your cuts to direct the mixture flow away from the exhaust port on the transfer ports! I always use the tarnish on the sleeve as a guideline to where I run the channels on the transfer ports...you don't want to make them so they are past the area where the case meets the sleeve, that would be useless! On engines where the transfer case ports are perfectly vertical I will sometimes remove some material in the case along the exhaust side to angle the port wall and direct the flow away from the exhaust port, but on the 2.5 there is just no need.(bits 4+5, 7+8, 9)
Sleeve before and after pics
(These sleeve pics are from a previous port job but are basically identicle)
Left transfer port
http://www.rcpics.net/view_single.php?medid=11279
Boost port
http://www.rcpics.net/view_single.php?medid=11280
Right transfer port
http://www.rcpics.net/view_single.php?medid=11281
Now for the case.... there really isn't much to do here because, the carb bore is already matched and the transfer ports continue directly down into the galley...the only thing I do to the 2.5 case is remove the material between the boost port and the transfer ports below the sleeve, this mod is usually seen in modified RB's and ensures maximum flow to the boost port since it is obstructed by the rear bearing and crankshaft counterweight. Make them so they are on and upswept angle toward the boost port. For this I use the Coarse Round bit (#1) followed by the Fine round bit (#6) going through the cylinder from the top and observing my progress through the backplate hole. Be carefull not to marr up the sleeve seating surface with the dremel chuck.
http://www.rcpics.net/view_single.php?medid=10752
http://www.rcpics.net/view_single.php?medid=10751
Ok...now you can polish what you feel needs it and clean everything twice or more before putting your mill back together. I usually will used warm soap and water with a small brush like an old toothbrush then rinse everything thoroughly and blow them off with compressed air. I don't recommend drying them with paper towel as you run the risk of fibers getting caught in your engine. When they are sterile and dry install your bearings in the case by heating the case just like before. Lay the outerbearing open side up on a clean workspace, take your hot engine and put it over the bearing and press down, it should slide right into the case without too much effort if it is straght and true. Then Slide the inner bearing open side to the crank onto the crankshaft and slide it into the case. I use a clean driver to press the crank and bearing into place, make sure the bearing is inserted all the way and let the engine cool. Well, you know the rest.
What to expect from your ported engine
If done correctly your ported engine should provide you with greater top RPM and a significant boost in power from the mids through maximum RPM. Coupled with a good low end pipe the engines broad powerband is awesome!
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Attachment 1: icon_wink.gif (image/gif)
Attachment 2: icon_cool.gif (image/gif)
Introduction
The TRX 2.5 is a well designed powerplant that doesn't need much porting to develop phenominal power, in fact it does quite well without any added port work. Being the Power Hungry folk that we are there is always a desire to try to pull more ponies out of our powerplants and that's where your trusty dusty dremel comes into play. Along with a steady hand and a ton of patience . I figure pictures are worth a thousand words so for the most part I will let them speak for themselves.
Bits I used to do this Job
http://www.rcpics.net/view_single.php?medid=10748
Before disassembling your mill, make sure that the engines exterior is completely free of debris. You can do this by blowing it off with compressed air and spraying it down with denatured alchohol. I also like to use a toothbrush to get the crust off and follow it all up with another blast of compressed air. When you are confident that no grit or sand will make it into your case and perhaps your bearings when breaking down your engine you are free to proceed. I remove the clutch assembly and the nut and flywheel first, followed by the head backlate and finally the carb.
I always look into the carb case bore after removing the carb to see if the crank window matches up flush with the carb case bore on the front and rear edges (not side to side). I also look for scratches on the crankshaft that wrap around the crank, clear signals that Dirt or debris has entered through the air filter. Look at the base of the carb, is the throat lip thickness equal to the matching lip inside the case? If not you will have to match these two surfaces either by coning the inside diameter of the carb bore or grinding away some material from the case bore. In the TRX 2.5 you have to do neither, the stock 2.5 carb is already portmatched to the case and needs no work whatsoever. The carb inlet is also tapered and requires no work, a welcome sight!
Next peer into the Exhaust port... Does the sleeve port line up perfectly with the case exhaust port? Do you see any Brass sleeve showing? On the TRX 2.5 this is also portmatched and needs no work. Now remove the sleeve rod and piston, followed by the crankshaft.
Time to remove the bearings from the case, this can be a real pain on stubborn engines! You will need to bake the engine in the Oven or toaster oven... Most recommend 350degrees for ten minutes, I find that they don't release at this temp most of the time. I just set my oven on the maximum setting and wait about five minutes. Pull the engine out wearing your oven mitt or pot holder and rap the engine on the countertop backplate down until the inner bearing drops out, if it won't budge heat it again for a few more minutes. After removing the inner bearing, turn the engine over insert the crank into the front bearing and give it a wiggle as you slide the bearing out of the case. Let all parts cool to room temp, bag your bearings in a ziplock bag to keep them free from particle contamination. Now you are ready to get down to business!
WARNING: Before you work on the crankshaft put a small peice of fuel tubing onto the rod Journal to protect it's surface from accidental slips with your tool!
I always start on the crankshaft. The TRX 2.5 crank is probably the only part that holds back the 2.5 from achieving maximum RPM and power. You will notice that the bore is very small but has a nice slope at the induction window. We want to bore out the crank considerably(bits 2+1 then 6+7), When I'm done boreing out the crank port, I usually knife edge the inside of the induction window on the crank that sits below the carb(bits 5+, you can see that on the 2.5 there is alot of material to remove, try to keep the integrity of the slope into the crank bore so the mixture enters as smooth as possible!
http://www.rcpics.net/view_single.php?medid=10750
Typically, I will then chamfer the area leading out into the crankcase (bits 4+7) before finally adding the scallop to the left side of the opening(bits 3+7)...
http://www.rcpics.net/view_single.php?medid=10749
If you choose to, you can follow up all your cuts with a polishing bit (like bit 9) and some metal polish such as Mothers or the ilk.
Next I do the sleeve, remember the order is up to you. Make sure you make your cuts to direct the mixture flow away from the exhaust port on the transfer ports! I always use the tarnish on the sleeve as a guideline to where I run the channels on the transfer ports...you don't want to make them so they are past the area where the case meets the sleeve, that would be useless! On engines where the transfer case ports are perfectly vertical I will sometimes remove some material in the case along the exhaust side to angle the port wall and direct the flow away from the exhaust port, but on the 2.5 there is just no need.(bits 4+5, 7+8, 9)
Sleeve before and after pics
(These sleeve pics are from a previous port job but are basically identicle)
Left transfer port
http://www.rcpics.net/view_single.php?medid=11279
Boost port
http://www.rcpics.net/view_single.php?medid=11280
Right transfer port
http://www.rcpics.net/view_single.php?medid=11281
Now for the case.... there really isn't much to do here because, the carb bore is already matched and the transfer ports continue directly down into the galley...the only thing I do to the 2.5 case is remove the material between the boost port and the transfer ports below the sleeve, this mod is usually seen in modified RB's and ensures maximum flow to the boost port since it is obstructed by the rear bearing and crankshaft counterweight. Make them so they are on and upswept angle toward the boost port. For this I use the Coarse Round bit (#1) followed by the Fine round bit (#6) going through the cylinder from the top and observing my progress through the backplate hole. Be carefull not to marr up the sleeve seating surface with the dremel chuck.
http://www.rcpics.net/view_single.php?medid=10752
http://www.rcpics.net/view_single.php?medid=10751
Ok...now you can polish what you feel needs it and clean everything twice or more before putting your mill back together. I usually will used warm soap and water with a small brush like an old toothbrush then rinse everything thoroughly and blow them off with compressed air. I don't recommend drying them with paper towel as you run the risk of fibers getting caught in your engine. When they are sterile and dry install your bearings in the case by heating the case just like before. Lay the outerbearing open side up on a clean workspace, take your hot engine and put it over the bearing and press down, it should slide right into the case without too much effort if it is straght and true. Then Slide the inner bearing open side to the crank onto the crankshaft and slide it into the case. I use a clean driver to press the crank and bearing into place, make sure the bearing is inserted all the way and let the engine cool. Well, you know the rest.
What to expect from your ported engine
If done correctly your ported engine should provide you with greater top RPM and a significant boost in power from the mids through maximum RPM. Coupled with a good low end pipe the engines broad powerband is awesome!
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Attachment 1: icon_wink.gif (image/gif)
Attachment 2: icon_cool.gif (image/gif)
