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      JUST IN!   04/24/2018

      HOW TO: 4-STROKE PISTON REPLACEMENT DONE RIGHT!

mrdsee

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About mrdsee

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  1. Yes the weight of the Eric Gorr piston being the same weight as stock keeps the crank/piston balance the same which keeps the over rev high as it's not fighting an out of balance situation. Plus it's a single ring so less bore resistance. Eric is also an excellent porter(included with 144 kit) and use to work for RPM. The piston is the secret weapon over other heavier piston 144 kits.
  2. I have a YZ125 with a Eric Gorr 144 kit with mid-top porting, his custom specced Weisco single ring piston(same weight as stock) with oil hole for exhaust bridge and skirt coatings, race gas head(needs straight VP110 or V12), 28-1 Yamalube-R, RB designs carb mod(Overbore, divider wing,etc) V-Force reeds, FMF Factory Fatty, and Titanium II Shorty silencer. It flat out hauls, good bottom end, flat midrange, wide band raped ape on top with almost unlimited over rev. That '06 with this set up would be sweet indeed.
  3. 70% rubbing alcohol not so good. 99% though works much better.
  4. "caused when the piston expands faster than the cylinder and the clearance between the piston and cylinder is reduced."
  5. "Problems with Wiseco pistons are almost always caused by one of these three issues: 1. Improper break-in-This can be a death sentence for a forged piston. 2. Improper warm-up-A great way to cold-seize the engine. This also kills crank and rod bearings, not just forged pistons. 3. Cylinder-to-piston tolerances too tight-You can't just slap a Wiseco piston into a brand new engine with no time on it. Forged pistons require about .002" more cold clearance than a cast piston. Once it's time for the first top-end job, a cylinder will usually have loosened up enough for the forged piston to have enough clearance. Most Japanese two-strokes spec .002"-.004" clearance for the OEM pistons. Wiseco specs .003"-.005" clearance. Another less common cause of problems with all pistons is when the person doing the top-end work doesn't drill the lube holes in the piston for an engine with a central exhaust bridge. A forged piston will actually tolerate this better than a cast piston. Anytime you rebuild the top-end, you have to measure the ring end-gap, and file the ring ends if neccessary. I rarely have a set of Wiseco rings that don't need to be relieved slightly. If the end-gap is too tight, the ring ends will hammer the locator pin right out of the piston, with devastating results. Wiseco specs .004" per inch of bore size for their ring end-gap clearance. All of these problems are caused by the mechanic that does the work, or the rider that's too lazy to perform a proper break-in or proper warm-up. You can't blame the product for your own incompetence (although that's usually what people do)."
  6. "To better understand why forged pistons are more seizure prone, you need to understand what makes a forged piston different than a cast piston. A cast piston is manufactured by pouring molten metal into a mold. The final shape is machined to it's final exacting tolerances. A forged piston is made by taking a chunk of metal, and beating it into shape with a die-press under enormous pressure. Like casting, the final shape is achieved through precise machine work. The main difference between a cast and forged piston is the grain structure. A forged piston is beaten into shape, and as a result the metal stretches and compresses as the piston takes shape. The varied, elongated grain structure is like fiber reinforcing, and it makes for a very strong piston. Microscopic cracks don't readily propogate through the structure of a forged piston due to the high density and the irregularly spaced and sized grains. A cast piston, on the other hand, is made up of grains that are all the same size, because it starts out as a liquid that, after being poured into a mold, undergoes a controlled cool-down process that allows the metal to reach a near-perfect equilibrium right out of the mold. The highly regular grain size and distribution makes them more prone to crack propogation and failure. The break-in of the two types is very different, because the metal properties are very different. The forging process produces a lot of internal stress from beating the metal into the intended shape. The stress is trapped in the metal of the finished part. A cast piston has lower internal stress, because it was able to seek it’s own internal equilibrium as the liquid metal flowed around inside the mold and then underwent a controlled cool-down. Since a cast piston has lower internal stress, it won’t distort nearly as much as a forged piston will when heated to a high temperature. The forged piston's propensity to distort when heated is the reason they require an elaborate break-in procedure. To relieve the internal stress, and maintain it's correct shape, the forged piston has to go through a series of heating and cooling cycles. As it heats up, the grain structure will re-distribute itself into alignment to relieve any trapped stress. As it cools, the cylinder will contain and restrain the piston, maintaining it's shape. After a few heat/cool cycles, the internal stress reaches equilibrium, and the piston will no longer distort when heated in the engine. It will maintain it's shape for the rest of it's life. Forging produces a higher grain density than casting, making the part much more durable under high-heat, high-load conditions. As long as you are patient enough to break a forged piston in correctly, you will have a piston that is more durable under extreme conditions."
  7. Higher octane fuel will tolerate a slightly leaner jetting if your jetting is on the leaner side currently. I have to run straight VP110 in my YZ144 since I have a high compression head. I also run a forged piston, so make sure you really warm the engine up prior to jumping on it with forged pistons as their expansion rates are different than cast pistons and will seize if not properly warmed up.
  8. Yep, good thing for the old dial indicator for finding out the correct timing. When one runs less oil the bike runs richer. Personally, I run Yamalube at 30-1 in 250's and have never had issues with oil or spooge, but the bikes are jetted correctly. Been riding YZ's since the '70's. At the altitudes your running, detonation is less of an issue than for those of us nearer sea level. If it were me I'd be running close to stock baselines, ie: timing, oil ratio, and jet for altitude and temperature.
  9. Also, was the rebuilt crank Weisco? I had a YZ250 and the rebuilt crank(Weisco) ended up being keyed 5 degrees off from stock.
  10. Why was the timing retarded? Was there detonation?
  11. Also, when you pull axles, put a light coating of grease on the shaft before reassemble to prevent them from seizing up in the future. Might also lube suspension linkage and swing arm pivot bearings. If the axles were seized, the suspension bearings are also likely to have been neglected. I'd also lube and adjust the steering stem and bearings also.
  12. High Temp RTV around the O-Rings
  13. Eric Gorr ported both of my YZ's (144,300) for Mid-Top. Plus did the head work, one for 91oct and one for straight VP110 or C12. Bikes flat out haul, and his work is stellar. Porting can in fact add HP. I would ask Eric, he has always been straight with me and very helpful.
  14. Exhaust tape, followed by a tin can strip, more tape, and then a couple of hose clamps. Should get you through a ride.
  15. Might also try running some Seafoam and/or Chevron Techron concentrate (Both available at Walmart) to clean out the fuel system. Has cured off idle and 1/4 throttle stumbles on some of my bikes that have sat for a while in the past. I found that running a tank with Seafoam followed by a tank with Techron worked best. Also try adjusting your fuel screw on you DRZ(I also have one of these) to see if it's set correctly. I like replacing the stock screw with one that can be adjusted easily on a ride when I'm doing high altitude rides since I'm normally near sea level. Half a turn or so in(leaner) and good to go in the mountains.