sezian Posted April 16, 2009 Share Posted April 16, 2009 Following my unfortunate seized engine I've had the barrel honed and ordered a new piston and rings. Unfortunately the new piston has arrived with only 2 piston rings - No oil scraper ring. My original piston had an oil scraper ring fitted, do I need to fit a new one? or just the normal 2 piston rings ??? To be perfectly honest I'm not sure what the oil scraper ring does, it's not shown in any of the manuals I have or any of the DT diagrams of piston and rings !!! Link to comment Share on other sites More sharing options...
Moderator Airhead Posted April 16, 2009 Moderator Share Posted April 16, 2009 How many grooves were in your old piston, there should be only two. Are you referring to the expander ring that sits under the second ring; If so re-use the old one. Link to comment Share on other sites More sharing options...
sezian Posted April 16, 2009 Author Share Posted April 16, 2009 Yes normal 2 grooves in piston. Please explain what this ring (expander ring) does ? I thought the piston rings expanded to fill the bore, why is there no mention of this ring in any of the manuals or the Yamaha exploded diagrams ??? Not sure if I can get the old ring out as the heat has welded the rings in on one side of piston !!!! Do I need to fit an expander ring ??? I'm guessing a lot of people would just go ahead and fit a new piston and rings if the new piston didn't come with one, it's only by chance that I found this ring on the old piston when I was cleaning things up, I've never before seen one. What's the point of it ??? I'm sure the answer isn't to expand the piston ring as there's enough spring in normal rings to expand themselves. Link to comment Share on other sites More sharing options...
Moderator Airhead Posted April 16, 2009 Moderator Share Posted April 16, 2009 Youre right, this expander ring is only supplied with genuine yamaha rings, thats why i would say re-use it, if you cant...then thats that! i dunno what its purpose is but obviously Yamaha thought it was a good idea. so you havent got an "oil scraper" ring, just two rings...thats good, what are you going to do to prevent a recurrance of the last disaster? Link to comment Share on other sites More sharing options...
sezian Posted April 16, 2009 Author Share Posted April 16, 2009 I'm still not quite sure what caused the seized engine, having examined all the evidence I can only put it down to being on full throttle for approx 3-4 miles, the bike obviously didn't like this and eventually overheated, causing the piston to melt some alloy and deposit this in the ring grooves and on the barrel. I've checked the 2 stroke oil pump and feed, which seems fine, when I took the engine apart there was evidence of 2 stroke oil in the inlet duct of the barrel, so I'm as confident as I can be that there was enough lubrication. The only other thing that could possibly have caused a fault was the mixture screw was 1 3/4 turns out and not 1 1/4 as it should be, I guess this could have caused slightly to much air to pass giving a slightly week fuel / air mixture. Other than that I have no idea what else could have caused the seizure. The one thing that I am slightly confused about is why the main fuse blew? Again I can only put this down to the bike overheating and the heat causing the fuse to let go ??? Link to comment Share on other sites More sharing options...
Moderator Cynic Posted April 16, 2009 Moderator Share Posted April 16, 2009 The only other thing that could possibly have caused a fault was the mixture screw was 1 3/4 turns out and not 1 1/4 as it should be, I guess this could have caused slightly to much air to pass giving a slightly week fuel / air mixture. Other than that I have no idea what else could have caused the seizure. The mixture screw doesent do much if anything at full chat its all on the main jet. Old strokers like these are not designed to be held flat out for long periods. Mind if you held your car flat out at max rpm how long would that last? Link to comment Share on other sites More sharing options...
Moderator Airhead Posted April 16, 2009 Moderator Share Posted April 16, 2009 The mixture screw doesent do much if anything at full chat its all on the main jet. Old strokers like these are not designed to be held flat out for long periods. Mind if you held your car flat out at max rpm how long would that last? Thats right if full chat is also full throttle, but could be full speed on 1/2 throttle on a flat road with a tailwind...worth considering? Link to comment Share on other sites More sharing options...
Moderator Cynic Posted April 16, 2009 Moderator Share Posted April 16, 2009 Thats right if full chat is also full throttle, but could be full speed on 1/2 throttle on a flat road with a tailwind...worth considering? Yep 'full chat' is full throttle, he said he was on full throttle for 3-4 miles and in the other thread he said he was on a DC. I would have said that will knacker ANY stroker. Link to comment Share on other sites More sharing options...
Moderator Airhead Posted April 16, 2009 Moderator Share Posted April 16, 2009 Ooerr, i didnt read the thread properly, full throttle for 3 - 4 miles, I find that when I do that it doesnt go any faster...just makes more noise!!, as you say the mixture screw is out of the equation at WOT ...so it just cruelty to elderly DT's then Link to comment Share on other sites More sharing options...
Moderator Cynic Posted April 16, 2009 Moderator Share Posted April 16, 2009 ...so it just cruelty to elderly DT's then Dispicable, shouldnt be allowed in a modern honest and upstanding society........ Link to comment Share on other sites More sharing options...
wild foamy Posted April 16, 2009 Share Posted April 16, 2009 Dispicable, shouldnt be allowed in a modern honest and upstanding society........ you really dont want to hear about what i've put my DT through then... im surprised it hasn't completely died and gone to the scrapheap in the sky... or maybe in a previous life it was a very bad bike, and now its punishment is to spend eternity being ridden by one 16 year-old after another, each adding their own "modification" and thrashing the bollocks off it to try and catch up with their mates TZR50 Link to comment Share on other sites More sharing options...
Moderator Cynic Posted April 16, 2009 Moderator Share Posted April 16, 2009 you really dont want to hear about what i've put my DT through then... im surprised it hasn't completely died and gone to the scrapheap in the sky... or maybe in a previous life it was a very bad bike, and now its punishment is to spend eternity being ridden by one 16 year-old after another, each adding their own "modification" and thrashing the bollocks off it to try and catch up with their mates TZR50 WF as far as DT punishment goes i'm pretty high on the list myself, i had a DT50m the one before yours on a w plate and on a good day she would crack 70mph. Recorded officially by a plod at 64 on a speed gun. (points mean prizes) On a ok day it would be an unridable pain in the arse and on a bad day bits of expensive ally generally got spat out the pipe............. Link to comment Share on other sites More sharing options...
sezian Posted April 17, 2009 Author Share Posted April 17, 2009 When I was a kid I’m sure I would have been full chat everywhere on my Garelli Tiger Cross and AP50. There was no other way to ride these bikes, it was always a race, especially when all you’re mates wanted to have the fastest moped on the bloc. I thought these old stroker’s were made for abuse !!! Having said that I’ve obviously learnt a lesson, no more duel carriageways and no more prolonged full throttle !!! Link to comment Share on other sites More sharing options...
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