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So I'm getting ready to start my 88 250R resto/ultimate duner project. I'm looking for advice on what motor you think is the best all around duner and leisure dirt racer. I will mostly be duning and all that comes with that, climbing, racing, general riding. I dont really need the biggest badest on the hill I want something reliable, nimble, good power from bottom to top. I was thinkin the esr 370 power valve but have been out of the R scene for a few years so I'm not sure whats all out there. Also what pipe to go with the motor.
 

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if your looking for a casual, reliable dunning, riding, racing, motor i would think 310 or 330 both are very reliable and offer a broad power range. the esr trx5 centermount is used by a lot of dune guys here for a play pipe. esr and ct are probably the two most well knows big bore guys. i recommend Neil (c-leigh racing) he's the site favorite and i dont think anyone has had a bad experience with him.
 

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I'd go with a 330 or 350. If you go with a PV, I would get the CT. Theirs works better than ESRs. If you have the extra cash, you should also have Neil port it for you. I've ran two 330s for several years now and the reliability has been great. We have a 350 now too and it has also been good so far. For an all around duner, the ESR trx5 is a good pipe. They have actually revised it so its even better now.
 

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the 370 is a good setup but for what it sounds like you want to do, I wouldn't rule out say a stock jug, 69 mm bore, 4 mil stroke setup. This motor set up with a dune port, ESR TRX 5 pipe, 40-41 mm carb, CR 250r ignition setup. This will get you approx 285 cc's but they flat rip if done right. I built one if these (okay so I have had a ton of motors over the years) they can out run a 310 and really perform as well as a 330, not quite as torquey but have a nice broad power band with the TRX 5 pipe.

Seems like everyone forgets about the stock cylinder but honesty that little 4 mil stock jug stroker was the funnest motor I have ever built and rode. These are a nice running and economical on the pocket book motor.
 

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So whats the difference in the trx5 and trx7 pipes?

They call the trx5 and "all around pipe". I would say it is like a TT pipe. More top end than an mx, but more low and mid than a rev or drag pipe.

The trx7 is the replacement for the trx6 which is for woods and mx. They also have a trx7 centermount, which Eddie strongly recommended to me. You get the same low and mid range power, but much better top end performance.
 

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i agree with atvcrazy, the oem jugs with a 4mm are a very nice little motor, and are cheap to build... Im going to build a oem 72 bore with a 4mm crank for my ole lady next.....
 

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Funny you mention the 72 mm bore, 4 mil stroke stock jug because my wife's bike has that exact same setup as we speak. I had a 1989 stock jug that I had an aluminum sleeve installed in so I could have the bore nikisiled. The combo that it uses is a 4 mil stroke with a YZ 490 rod and a very light weight KTM 300 72 mm flat top piston. uses a .040 thick gasket that I had cometic gaskets make for me. Piranha Pete did a dune port for it and it runs real good. I used the stock head and had it recut so it looks factory without the spacer plate.
 

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Funny you mention the 72 mm bore, 4 mil stroke stock jug because my wife's bike has that exact same setup as we speak. I had a 1989 stock jug that I had an aluminum sleeve installed in so I could have the bore nikisiled. The combo that it uses is a 4 mil stroke with a YZ 490 rod and a very light weight KTM 300 72 mm flat top piston. uses a .040 thick gasket that I had cometic gaskets make for me. Piranha Pete did a dune port for it and it runs real good. I used the stock head and had it recut so it looks factory without the spacer plate.

this sounds like what I'm going to do. Why not use the ktm300 rod? just curious, that would give the same ratio as the CR motors. Who did the crank? where did you get the sleeve?
I'm very familiar with flat top or 2 degree pistons. Thanks...
 

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this 4 mil stock jug sounds interesting, i was considering buying one of the new ESR 310 jugs for 600 bucks. How much would it cost me to build one of these 4 mill stockers, and would the power be comparible to the 310 Right now my motor is completely stock except for a pipe, is the 600 dollar 310 gonna be worth it power wise.
 

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I got the aluminum sleeve installed by Millenium tech, the place that does all the nickasil liners. This was a 89 cylinder and they just happened to have the sleeve in stock. I don't know if they make these anymore or not. But honestly, the 284 cc (69 mm bore, 76 mm stroke) that I had would run neck to neck with this 72 mm bore motor and the beauty of the 284 cc is you can get a hot rods 4 mil stroker crank, a 69 mm wiesco piston, and have your stock jug ported all for a pretty fair price. It's easier to buy a 310 or a 330 and slap it on but I think it's cool to run the stock stuff and it's pretty amazing what kind of HP you can make out of the stock stuff and keep some good reliability.

If you are still interested in the big bore, I know that NW sleeve in Gresham, Or will install a 72 mm bore steel sleeve for about 150.00, then you will have it ported after this. I bought a hot rods 4 mil crank and had the YZ rod put on it by Hybrid Engineering in Camas, Wa. Total cost of the crank was $480.00 after purchase price and rod install. You can also have Crankworks do the same crank. You can run the KTM rod but I just like the YZ 490 rod/stroke ratio better. With a 4 mil crank it puts it back to 1.80, the same as a stock stroke long rod 250r. I also got the port timings I wanted with the KTM piston without having to deck the bottom of the cylinder to make the cylinder shorter due to the pin height of the KTM 300 piston.
 

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Based on your comments the +4mm crank, KTM 132mm rod and KTM piston the piston will be WAY low to the top of the deck? The YZ rod is like 5.5mm(?) longer than the KTM rod.

Do you know the distance from the c/l of the piston to the timing edge of the KTM 300 piston?

I like the shorter rod ratio of the CR motors especially with a PV

1.8 to 1.82 is great for mid range no doubt about it!
 

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KTM 300 pin to crown measurement .710

I have the stock gasket in my wifes stock jug 4 mil stroke 137.5 mm rod length motor and it's port timing is about 188-190 degrees on the exhuast port. You might get away with it with the KTM rod but it's going to be close. My guess you will have to deck the bottom of the cylinder
 

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KTM 300 pin to crown measurement .710

I have the stock gasket in my wifes stock jug 4 mil stroke 137.5 mm rod length motor and it's port timing is about 188-190 degrees on the exhuast port. You might get away with it with the KTM rod but it's going to be close. My guess you will have to deck the bottom of the cylinder
Which KTM 300 piston?

91-94 300 pro-lite PK1635 631M07200
96-03 300 pro-lite PK1636 712M07200
04-07 300 pro-lite PK1408/9 858M07200
 

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Just curious, are these OEM KTM pistons that you guys are using
 

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I am running the 858MO7200 and yes these are OEM KTM pistons. This piston was feather light at one time but I don't know now because Wiesco seems to have quit machining pistons all the way anymore for some reason.
 

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I am running the 858MO7200 and yes these are OEM KTM pistons. This piston was feather light at one time but I don't know now because Wiesco seems to have quit machining pistons all the way anymore for some reason.
Thanks - I called WISECO today and they gave me the dimensions. The one you have is the best one but it's still only 76mm long....just long enough if at BDC your piston goes just under flush.
I was hoping that piston was 77 or 78mm long.

I'm on the fence on which piston to use. Probably the KTM.

Thanks again.
 

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in combination with the 137.5 mm rod it was the best one. I believe another one of these KTM pistons is a flat top that has the same basic piston pin placement as the 86 ATC/TRX piston at 1.142". I can't remember if it's a flat top or not, I believe it is. This might be a better combo with the KTM 132 mm long rod. Will be a slightly taller spacer plate than what you would put in for the long rod conversion of the short TRX rod vs the longer rod.

I don't know what stock cylinder you are thinking of using but depending on the porting you do, it's harder to get the exhuast port raised with the 86 cylinder vs the 87-89 cylinders with a stroked crank. Seemed like when we were doing these the 86 cylinders water jacket was actually bigger and lower in the cylinder compared to the newer models. Honda must have revised the port timings and actually raised them after 86 so they had to make the depth of the water jacket shallower to compensate for this. All motor builders have differing opinions on which model year cylinder they like the most. I like the 86 cylinders because it has a better intake port but the transfer tunnels aren't the best. Some like the 87 the best, and some like 88-89 the best.
 
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