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Found 23 results

  1. Hi folks, I recently purchased a Honda CR80 from a friend. It was sitting in a shed for 3 years and was beat pretty hard in the past I believe. I took the opportunity to get my first bike for cheap knowing I would have to fork out some cash on it. The main issue I found was that the crankshaft seal on the clutch case side was shot so I replaced it the bike started to run ( did not even idle when I got it). The issue I am having now is that when at WOT it revs high but then start to bog down it only happens on WOT. The lower RPM range is fairly clean and responsive but if i go WOT it goes up and then falls off hard. I have check the main jet, primary jet and float bowl height as well. Any ideas you guys can come up with will be much appreciated !
  2. Hi all, I've recently purchased a kx80 for my son's first geared bike, was told it's a 1994 but the frame number turns out to be a 1998 I think, after 1 hour of riding it started spitting water out the over flow and leaking from the cylinder head, upon inspection after taking off the head, the previous owner has wedged screwdrivers between them to split and has botched the bike together, now the top of the barrel and head is absolutely knackered. The engine is a 1989 4 stud top end, could i possibly change it to a newer 5 stud top end and would I need to change anything else with it. Thanks in advance. Bristol, UK
  3. Hey guys. Im rebuilding the too end in my 2017 TC 250. Should I hone the nikasil cylinder or not. There's no scratches really just a couple of tiny scuffs. Can't feel anything with my finger. Can still seem some cross eteching at the bottom.of the cylinder. There was about 70 hrs on the last piston ? Also should I take the power valve off and clean it out? Thanks
  4. Hello. Rebuilding my top end as the valves have stretched and need to be replaced. I need some confirmation of a few things: Are both the intake and exhaust valves titanium? Or just the intakes? Which piston should I go with for maximum longevity? OEM or aftermarket? Thank you
  5. Rebuilding the top end on my 1999 YZ125, what is the best method of honing to bring back the cross hatches? What color Scotch-Brite? Green or red? Also anything that would help out a first top end rebuild, I see all these threads about people rebuilding the top end & it blows in a few hours. I do not want that to be my case, it seems so simple why are people running into complications? Thanks!
  6. I am rebuilding the top end on my 1993 kx250 dirt bike. Ive never done a top end before, and i was wondering how much it would cost. Also, how can i tell if i need my cylinder re plated? Does anybody have any piston kit brands for me to consider? TIA
  7. Hi I have a 97 cr250 and I'm wanting to order a new top end complete or "kit". I wanted to get the s-3 racing kit. But it says it's for 99 and up. Can't find any big bore cylinder for it . What makes the 99 motor so different from the 97.
  8. Hi there! I have an 86 xt350. It was blowing air and fuel into the air box. It wasnt running when i got it. I knew the guy before me had installed a new piston. I adjusted valve clearance and still was getting air and fuel in the air box. Thought maybe, timing was set to overlap instead of tdc. So i turned the crank 360 degrees and set the cams to match the timing marks on the caps and tried again. Still blowing air/fuel into air box. Took head apart. Both intake valves bent. Missing all 4 spring seats and oil seals. Now for the question. (Im new to this and learning) How do i find tdc without the head installed. I would hate to get new valves and bend them again. Can i just put the cams in with timing marks oriented with marks on the cam caps and the mark on the rotor oriented with the timing mark on the case and call it good or will i need to ensure its at tdc as opposed to overlap. In my mind it seems like i would have to ensure im at tdc. Otherwise the spark plug would be be firing at top of exhaust stroke as opposed to compression stroke. Thanks for your time!
  9. Hi, I am doing the top end on my ‘19 Yz125x. The cylinder has the letter C at the back so do I put a C piston in it? I just ordered 2 C size pistons for the next two top ends. Will it be fine? Thanks!
  10. Hi, I am replacing my piston and it’s bearings and rings and the top end gadgets. So a top end I guess 🙂. It’s a ktm 250 2stroke (2016) and it’s has 300 hours. The piston has been changed before but not by me so I don’t know if any work was done to the cylinder. Now the bike didn’t blow up and I can’t feel or it see any horizontal scratches so I am good in that department. But do I have to hone or deglaze my cylinder? I hear a lot of people saying not to touch it like less is more and other people say you have to deglaze them or get them honed? What should I do? Or use scotch bright to make more criss cross hatching for the rings to seat better I guess that’s deglazing as well. Or just keep running it as is since there are no scratches. Don’t know what to do. Any ideas? What do u guys do?
  11. We know this is technically 'Thumper'Talk, but we also know a lot of you have 2-strokes in your garage. We want to share some tips we put together that will help you prevent and diagnose potential problems with your 2-stroke engine. Bookmark this maintenance guide to help keep your bike on the track or trail and off the bench! Article by Paul Olesen. Two-stroke engines have a storied history of being finicky beasts. If you’ve been around two-strokes for any length of time, you’ve probably heard stories that start and end to this effect: “It was running amazing...then the next thing you know - it blew”. We find these stories interesting, and empathize with the unfortunate owners or riders who tell them. At the same time, however, it is often wondered if there were any signs that could have predicted the fateful date with destruction. Photo: Steve Cox We're going to discuss and share a number of observations and diagnostic tests that can be performed to help identify whether or not your engine is going to leave you in the unfortunate role of the broken engine storyteller. While many operators are insistent that their engine gave up without warning, this is often not the case. We’ll start by going over observations that can be made with the engine running, and progress into diagnostic tests that can be routinely made to assess engine health. Recognizing Symptoms Startability Does the engine struggle to start when kicked, but is more prone to coming to life when the electric start is used or when the machine is bump started? Poor starting under normal conditions is not an inclusive sign that the engine is doomed to a spectacular failure, but it is a sign that something is amiss. Carburetion or injection issues are possible, but the bigger potential issue to be aware of resides within the cylinder. Worn piston rings can cause incomplete sealing, resulting in lower compression and more difficulty in starting. Worn piston rings or reed valves that are no longer sealing properly may be the cause of the poor startability characteristic. When the piston rings don’t seal properly, the engine doesn’t build good compression, so when kicked, the engine struggles to come to life. Similarly, if the reed petals are damaged or broken, less air will be trapped in the cylinder. Push the machine or use electric start, and the compression event is shortened via faster rotational speeds, which may be just enough to bring the engine to life. Damaged or worn out reed petals will allow air to leak out, creating less cylinder pressure and starting/running difficulties. Inconsistent Performance Does the engine struggle to hold a tune, or seem like the jetting constantly needs attention, despite relatively stable atmospheric conditions? Sporadic running is not always a death sentence, but should be investigated further. A dirty carburetor or worn spark plug can contribute to this behavior, but the problems that can lead to catastrophe are worn engine seals or gaskets. Stator side crank seals, leaking base gaskets, or intake manifold gaskets are all examples of seals that will result in air leaks which can lean out the air fuel ratio. Lean air/fuel ratios when running at full power can result in excessive combustion temperatures, which can melt a hole in the piston or seize them in the cylinder bore. Ignoring the possibility of a bad gasket or seal isn't worth the potential damage, especially with the affordability of OEM quality gasket kits from ProX. Gearbox Oil Consumption Loss of gearbox oil is abnormal, and in all cases should be able to be traced back to leaking seals or gaskets. In the unlikely event the bike tipped over or cartwheeled, gearbox oil can occasionally exit via the gearbox/crankcase breather. If the gearbox is losing oil but the leak path cannot be identified externally, there is a good chance the drive side crankshaft seal is leaking and allowing the gearbox oil to migrate into the crankcase. During the scavenging process the oil is transferred up into the combustion chamber and burned. Tracking down a leak like this and finding you need new crankshaft seals will commonly turn into a bottom end rebuild job. If you're going to tear into the bottom end to replace seals, that same amount of wear the seal experienced could be evident in other components as well, including your crankshaft and bearings. Not only does ProX make it easier to tackle a bottom end rebuild with our rebuild guide (10 Tips for a Dirt Bike Bottom End Rebuild), but one of the most recent additions to the OEM-quality replacements parts lineup are complete crankshafts. Dropping in a complete ProX crankshaft paired with a main bearing and seal kit is an affordable option for reliable performance. ProX crankshafts are assembled with double-forged, Japanese steel connecting rods, as well as Japanese big-end bearings, crank pins, and thrust washers, all manufactured by OEM suppliers. Excessive Smoke After Warm Up Since the engine is burning pre-mix oil we have to be careful here, because blueish-white smoke is a normal occurrence of two-stroke engine operation. However, excessive smoke after warm up can be an indicator of a couple problems. Blue smoke exiting the exhaust pipe after the engine has warmed may be a sign that gearbox oil is burning in the combustion chamber. While I would never encouraging sniffing your exhaust, combusted gearbox oil will have a different odor than the normal pre-mix oil the engine is using. White smoke exiting the exhaust pipe after the engine has warmed may be a sign that coolant is burning in the combustion chamber. The root of this problem is typically a leaking cylinder head gasket or o-rings. Excessive Coolant Exiting the Overflow Tube While it is common for coolant to exit the overflow tube when the bike has been tipped over or when it has overheated, it should not occur regularly. Coolant blowing out the overflow tube is another good indicator of a leaking head gasket. Note where your coolant overflow line runs, so you can keep an eye out for overheating issues. Coolant Weepage Dribbles of coolant exiting the engine around the coolant pump are indicative of a faulty water pump seal. If left unattended, the entire cooling system will eventually empty, causing overheating and an incredible amount of damage. Excessive Top End Noise Isolating top end noise in a two-stroke is easy since the only moving component is the piston assembly. Discerning what is normal takes a trained ear and familiarity with the particular engine in question. However, audible cues often present themselves when components wear or clearances loosen up. The most common noise associated with a two-stroke top end is a “metallic slap”. This is commonly referred to as piston slap, and is a result of the piston rocking back and forth in the cylinder bore as it reciprocates. This phenomena is normal, but the intensity of the slap will increase as the piston skirt and cylinder bore wear. Left unattended, excessive piston slap can result in failure of the piston skirt. Check out our complete 2-stroke top end rebuild guide here. Excessive piston slap can cause damage to the piston and weaken the skirts. It's important to check piston-to-wall clearance when installing a new piston to ensure a long operating life. 2-Stroke pistons fitted with skirt coatings also help reduce friction and operating noise. Diagnostic Checks & Tests Engine Coolant Coolant contaminated with black specks can often be traced back to a leaking head gasket or o-rings. Combustion byproducts are forced into the coolant system due to the high pressures in the combustion chamber during the combustion event. These black specks will often float and show themselves as soon as the radiator cap is removed. Gearbox Oil The composition of the gearbox oil can provide a lot of clues as to what is happening within the engine. For starters, what color is it and what is in it? Oil that appears milky is a good indicator that moisture is finding its way into the gearbox oil. The most common culprit is a faulty oil side water pump seal. A keen eye can spot various metallic particles within the oil itself. Aluminum will appear silvery gray. Bronze particles will have a gold shine. Ferrous particles will be dull and are often more discernable by dragging a magnet through the oil. Accumulation of all of these aforementioned particles will be normal in small quantities, but excessive amounts of any of them could be cause for concern. Fortunately, since gearbox and power cylinder lubrication are separate the number of causes for problems is limited and more easily pinpointed. Other than changing your gearbox oil regularly, keep an eye out for metallic particles, as those can be a sign of accelerated wear on internal parts. Cylinder Leak Down Testing While less commonly prescribed on two-stroke engines, performing a cylinder leak down test is by far one of the most definitive diagnostic procedures that can be performed to determine the health of the piston rings, cylinder bore, and cylinder head seal, whether gasket or o-rings. If any of the previously mentioned symptoms are observed, a leak down test is almost always a great next step. A leak down test pressurizes the engine’s combustion chamber and compares the amount of pressure going into the combustion chamber to the pressure that is retained. Pressurized air is administered via the spark plug hole and two pressure gauges are used to make the comparison. The piston is positioned at top dead center. Air exiting the combustion chamber can then be traced back to the piston rings or cylinder head seal. Compression Testing A compression test can be an tell-tale indicator of the health of your top end components. Be sure to compare your reading the manufacturer's recommended compression measurment. A compression test aims to quantify how much pressure builds during the compression event. A compression tester which is connected to the spark plug hole consists of a pressure gauge and a one way check valve. The engine is kicked repeatedly or turned over a number of times using the starter. The resulting pressure that is recorded can then be used to assess the health of the cylinder bore. Low pressure readings can then be attributed to problematic piston rings or leaking cylinder head seals. Crankcase Leak Down Testing A crankcase leak down test is utilized in order to assess the sealing integrity of the crankcase and cylinder. Personally, this is one of my favorite tests to perform because of its ability to isolate a number of potentially problematic seals and gaskets all at once. Components such as crank seals, base gasket, and power valve seals can all be checked to determine if they’re leaking. In summary, a crankcase leak down test is performed by sealing the intake manifold, exhaust outlet, and any power valve breathers. Then the crankcase is pressurized under low pressure. Typically, the goal is to retain the pressure in the crankcase over a set length of time. Loss of pressure is indicative of leaks, which can then be traced to their cause. Preemptively replacing components before the engine suffers a major failure is both safer and more affordable than dealing with the problem after the engine has stopped working entirely. Most problems that can occur within the two-stroke engine can be mitigated by servicing components such as pistons, rods, rings, bearings, seals, and crankshafts. Many riders dread the thought of having to service these items due to the excessively high costs associated with OEM or premium aftermarket parts. Fortunately, brands such as ProX offer a comprehensive lineup of OEM-quality components at reasonable prices, many of which are produced by OEM suppliers. Depending on what you need to service, components such as piston kits, connecting rods, crankshafts, bearings, gaskets, and seals can all be found in the ProX catalog. Replacing components as part of preventative maintenance can save time and money, especially with the availability of affordable, OEM quality parts. Find ProX parts for your machine here. Discussing specific time intervals in regards to when things should be replaced is futile. The reason is simple: different engines, maintenance practices, and applications will all have different intervals. Installing an hour meter on your engine so that you can log the number of hours the engine has run can be one of the most insightful ways to establish maintenance and replacement intervals specific to your engine, riding, and maintenance habits.
  12. Just curious on how many hours do you usually run a piston? Or just how hard you ride
  13. Hey everyone, I'm hoping some of y'all can help me out with some advice. I always liked reading threads like this one. Hope it's ok posting here in the Kawasaki forum even though it's an RM100. It's supposed to be the same bike right? My girlfriends 2003 RM100 started rattling one day while out riding. There was power loss and it stopped running but would still turn over. Fast forward to yesterday, we took the top end apart and checked the crank for play. The piston has some marks on it as well as the cylinder. I took some measurements and the piston and rings were at the service limit, but the cylinder was still in the acceptable range? This is my first two stroke rebuild and any advice would be great. If the bottom end needs a rebuild along with the top end, I'll probably take it to a mechanic ?.
  14. I have a 2015 kx250f with around 65-70 hours on it and I’m not sure whether I should rebuild the top end or not. It has been maintained very well, only ridden on trails, the valves were just adjusted, and there are no signs that indicate a worn top end. Is it ok to keep riding until it shows signs of needing a rebuild, or should I just rebuild it now because of the high number of hours? Apologies if this is a stupid question, I couldn’t find anything on the internet about it.
  15. I recently rebuilt top and bottom end. Heat cycled it, break in, ran fine. First ride, an hour in, it died and would not start again. Lost almost all compression. Has 15 psi on compression test. I have cylinder pulled off, piston and ring looks fine. Head gasket looks fine. Tightend head studs, they were a little loose. Head doesn't seem to be warped at all. I'm at a loss. Any ideas would be appreciated.
  16. Are there any go-to parts places for these old kdx's? Or anybody that you guys recommend I send my cylinder too? I traded my old kz550 for this kdx last week and the only reason I agreed to the trade was because the kdx supposedly had a brand new crank and top end with low hours on it. It ran good enough to make the trade and had great compression, just needed some carb tuning, it had a good knock to it but everywhere I researched said that its normal and it's only the kipps valves. As soon as I got the carb lined out, the con rod bearing went out, taking my piston and cylinder with it.. idk why it failed, con rod says "royal" on it but other than that, idk what brand any of the parts used are. Havent dug too deep yet. Just want to get it running as cheap as I can since I traded off a dang nice bike for this thing and now I'm kicking myself for doing so.. I have to many project bikes and I really didnt think I was getting another one.
  17. Recently just rebuild my 250 SX due to low compression. Slapped in a new forged Woessner and gotta break it in today. The old cast vertex really took a beating, it somehow looks like the bike is running too hot/lean? Main Jet is up a size already.
  18. I have an 2002 cr250 and the bottom end crank bearing seized. While taking the motor apart the top end looks to be in excellent shape and I just replaced it two rides before the bottom end locked up. Do I need to replace the top end as well? I already ordered all oem parts for the bottom end but am not sure if I need to replace the top end. I can post pics of the top end later today. Thanks ya'll
  19. Near the end of this season my klx125 started to smoke a bit. I just took apart the top end to find an excesive amount of carbon build up on the top of the piston and head. I was surprised as the bike runs fine besides the small amount of smoke. Bought the bike used last year and this is the first time I've had the top end apart. Any ideas of what could cause this build up???
  20. Just ordered a oem top end kit for my 1999 YZ125. The bike runs perfectly, I'm just rebuilding for preventative measures. Is my cylinder nikasil plated? I ordered a ball hone since my cylinder is glazed. After some research I discovered that honing a two stroke cylinder isn't a good idea because of the ports. I'm taking my cylinder to get measured to see if I'm still in spec. I also will be measuring the ring gap with a feeler gage. Anything I'm missing to make this top end rebuild go flawlessly?
  21. I was looking at putting a Prox Piston in my kx 250 for my next rebuild. Have other things to get don't really want to buy a wiseco. How durable would it be in my bike, how long would it Last. I ride Michigan trails. Usually pretty tight averaging 30 mph. Also, ride Hatfield McCoy. Dont usually get on it hard besides the occasional drag race with friends. Would this Piston last a summer in my bike I will rebuild every summer anyway. Probably put 50-60 hours on it a summer maybe closer to 40.
  22. Anyone on here that can assist? I have an 08 TTR 230 that was burning oil. I removed the top end, installed a new piston and rings, reinstalled everything. When I started it, it ran for 3-4mins with the choke on (no oil burn). When I turned off the choke it stalled with a clunk from the crankcase. I removed the cover for the cam chain sprocket and found that the bolt has dislodged and the sprocket popped off. I attribute it to the tensioner being too tight. When I reinstalled it it was fully extended ( I didn’t know to turn it in baggies installing. I replaced everything but it won’t start. Turns over nicely, has spark, good compression, but won’t start even with quick start. Wonder what else could have been damaged when the sprocket came off. Thx.
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