4stroker Posted October 16, 2007 Report Posted October 16, 2007 on a trex motor, should the transfers and intakes be completely uncovered at BDC Quote
Bansh-eman Posted October 16, 2007 Report Posted October 16, 2007 i dont think they are completly open. but im not 100% maybe someone else can chim in that has used them .... Quote
4stroker Posted October 17, 2007 Author Report Posted October 17, 2007 yeah its a 7mm stroke, 72mm bore Trex. was purchased from DASA about 3 years ago and assembled here in australia. it seems that the transfers and even the exhaust port are partially covered by the piston at BDC. its almost like the cylinder is meant for a 10mm crank, however at TDC the piston is flush with the deck.... who is a reputable source we can talk to about this particular style of motor (TREX)? we rang DASA but they werent much help, they were very vague and pretty much said "yeah thats how it should be" we are having reliabilty issues with this engine and things like this arent instilling much confidence in us to gt it sorted! can anyone point us in the direction of a "t rex guru"? any help much appreciated! thanks, mark Quote
moneybags Posted October 17, 2007 Report Posted October 17, 2007 My new 4 mill motor is like that. At BDC. The pistion sits above the bottom of the exhost port. When I first saw that I was like WTF. but dident question it after I road it. With my 421 motor. At BDS the pistion sits flush with the pistion. Dont know I am even more confused now. I think that K&T porformance it a big T-rex builder. They should beable to help. Quote
06BaNsHeE Posted October 17, 2007 Report Posted October 17, 2007 Give K&T a call.There good with trexes Quote
06BaNsHeE Posted October 17, 2007 Report Posted October 17, 2007 Why dont you just sell the motor and go with a 7mm Cub? Quote
locogato11283 Posted October 17, 2007 Report Posted October 17, 2007 call k and t. they prolly have more experience with t rex than anyone. also, i do believe that almost every motor ive had the pistons are just a little above the exhaust.. Quote
4stroker Posted October 17, 2007 Author Report Posted October 17, 2007 Why dont you just sell the motor and go with a 7mm Cub? this engine is used for flat track and oval track speedway, short and long circuit have no interest whatsoever in a non pv cub also want to learn something and sort this thing out rather than giving up and going with something else... thanx everyone else for your input will give k&t a ring today and see if they can help Quote
Bansheeman11 Posted October 17, 2007 Report Posted October 17, 2007 I think that the piston should just come flush with the bottom of the exhaust port (doesnt really matter though) but surely the transfers cause this will interfere with flow. We run a 4mm and 16mm T Rex for flat track racing and are very pleased with the set-up once you get it dialed in. These issues should not be causing reliabilty issues though. What problems are you haveing, we might be able to help. Maybe you could put a thicker base spacer in and machine off the top of the cylinder. but remember this will raise the exhaust port duration! Quote
4stroker Posted October 17, 2007 Author Report Posted October 17, 2007 what exactly have you had to do to get it dialled in... pm if you like! this thing we are running the top end doesnt last more than a few hours (if that) we are running way rich jetting (39mm keihins, eek needles on the 2nd highest clip, 180 main jets) and it still nipped up the right side doing a plug chop on a fresh top end it is running 3.5 thou bore clearance, and an 8mm squish with 32thou clearance. we are thinking of increasing bore clearance to 4.5 thou and squish clearance to 45 thou... what do you run the port openings is just something we noticed while having it apart and thought it may contribute to finicky jetting requirements what does your t rex motors rev to. this one revved to 10200 when it died... also do you cut the window on the pistons to match the intake ports. coz on this particular motor the piston skirt covers up half of the outside intake ports.. if you know what i mean.. Quote
4stroker Posted October 19, 2007 Author Report Posted October 19, 2007 what should the exhaust and transfer port durations be on a trex? (roughly) this one only has 182 degrees exhaust and 120 degrees transfer, which seems very mild to me? Quote
Bansheeman11 Posted October 23, 2007 Report Posted October 23, 2007 Yeah 182 degrees is well low for the exhaust port, we dont go as high as the drag racers do but i would recommend 198 duration for your engine size and application. also i wouls take the transfers to 126 degrees, maybe more, but not over 130 degrees. The big thing we find with these motors is getting them to run cooler, i hope you have a high capacity rad and high flow impeller for a start, but we also run an extra rad on the 16mm and some in-line coolers. we run the squish at 1.1mm clearance. As for bore clearance, you sound a little tight, we run about 6.5 thou to be safe, there is just no point being too tight with the Trex. How is it nipping, aroung the top or bottom of piston, exhaust side or all round? Also what is the outlet size of your stinger pipe. Sorry for the slow responce but i do not log on all the time, you just gotta be patient!! Any Q's please ask. Quote
4stroker Posted October 23, 2007 Author Report Posted October 23, 2007 thanx for your reply man it is nipping up al around the piston... some more bore clearance should fix the problem though we are worried that we have the wrong cylinders for the 7mm crank, as none of the port timings make any sense.. also like i said none of the port floors are flush with the piston at BDC, they are all below... but the piston is flush with the deck at TDC. base gasket surface to head gasket surface is 108.5mm... does this sound right? do you cut the windows of your pistons to fully uncover the intake? thanks again, mark Quote
Bansheeman11 Posted December 11, 2007 Report Posted December 11, 2007 thanx for your reply man it is nipping up al around the piston... some more bore clearance should fix the problem though we are worried that we have the wrong cylinders for the 7mm crank, as none of the port timings make any sense.. also like i said none of the port floors are flush with the piston at BDC, they are all below... but the piston is flush with the deck at TDC. base gasket surface to head gasket surface is 108.5mm... does this sound right? do you cut the windows of your pistons to fully uncover the intake? thanks again, mark Hi Mark, sorry it has been so long for me to reply, unless you have already sorted your problem, i think i might have a solution, if you give me the measurement from the top of the cylinder to the bottom of the exhaust port and also the overall height of the piston at the edge. you can email me on [email protected] for a quicker responce! Quote
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