sezian

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 !!!

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 ???

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.

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 !!!

Hi Paul, thanks for the reply. I had just completed the rebuild although I used the old piston and rings, maybe this was a mistake? I did also manage to remove the oil bleed screw on the pump and get shot of any air, the oil pump was fully bled and had full 2 stroke oil right through the tube as you had previously advised. I'm not sure what caused the bike to seize, perhaps it was to much full throttle for an extended period, although I did think these bike were fairly indestructible ??? I only mention the weak spark theory as it was mentioned to me as a possible cause, although the engineering shop did say after I picked up the barrel that he thought it was probably a fuelling fault ? I did have the mixture screw on the carb turned out 1 and 3/4 turns from fully in. Having gone through the manual I now read the screw should only be turned out 1 and 1/4 turns, was this a possible cause ??? Any thoughts, suggestions, what should I check before re-buid ??? Thanks.

Just got my bike MOT'd and on the way home (flat out down the duel carriageway) she feels like she’s about to seize, so quickly in with the clutch and coast to a stop !!! No ignition lights? Checked the main fuse and that’s blown, put the spare in, I now have ignition lights back, but when trying to kick the bike over there’s very little compression !!! Wait for the nice RAC man who has a quick look, we remove the spark plug and kick it over, he say’s there’s a spark but a week one. Eventually I get loaded on a trailer with the bike and get home after a couple of hours sitting by the side of the road. So off with the head and barrel, the rings have welded themselves in the groves and the piston has some lovely scars, the barrel looks marked although according to my local engineering shop it only needs honing out, but he does say something has obviously caused the problem ??? So what was the cause? The engineering chap said a week spark could cause it? Is there a way to test the ignition coil? Having looked on the web (wemoto.com) my coil looks different from the replacement part, in fact it looks more like an early version DT coil ??? I’m now pretty confused, is there anyone who can possibly shed some light on why the bike seized and what the difference is with these ignition coils. Many thanks.

Unfortunately I couldn’t undo the screw and this turned into a bit of a nightmare. I decided to pull the oil feed pipe off that’s connected to the pump and bleed it that way, after all the pipe is right next to the screw, when the oil was flowing freely I went to put the pipe back on but noticed a small slit in the back of the pipe. So I cut a very small length off, now trying to pull the pipe a little to get it back on the whole thing came away in my hand !!! You can imagine I was not amused, oil pi**ing out and there’s no way you can get to the other end without taking the side casing off. Anyway after a few hours work and much swearing it all went back together. The screw is still fixed so I can’t bleed from that and I know there’s good flow from the oil tank to the pump, the pump is aligned correctly and working fine I guess it’s just a bit of patients and running the engine slowly until it’s all bled through.

I did try this but it didn’t have much effect. I will work on this method again (unless you can offer any other suggestion) and try to disperse all the air. But just to confirm should I see a completely full oil pipe all the time ?

Can someone tell me if I should see a constant flow of 2 stroke oil from the oil pump to the carb, ie should the small clear plastic pipe be full of oil all when the bike is running ??? Having just got the bike up and going I’ve noticed the oil pipe appears to be sending oil in small slugs with lots of air pockets between oil delivery. I’m not exactly sure how the oil is fed, the pump is working but is the oil drawn via some vacuum from the carb ?

Many thanks for the info. The Image Works (www.bike-stickers.com) have been great, new exactly what I wanted and were cheaper than others. Should get the full set of decals in about a week, so will post what I think of quality etc.

Thanks Ron, I just checked the web site and unfortunately it would seem they don't do the "Hockey Stick" type graphics for the DT175MX. This may be because these decals were for the Uk / Europe ??? Anyone else able to offer any help ???

It would appear my fuel tap is weeping fuel when turned on, only a very slight leak and doesn’t seem to cause any running problems however I obviously want to fix it. Is there anyone selling fuel tap repair kits for a DT175MX ???

Not sure what bike you are refering to but it could be: 1) Turn singnals / flashers may only work when the engine is running especially if it's a 6 volt system. 2) Again headlight may only work when the bike is running, the side light should come on with the ignition but headlight will only work when the engine is started. Have you tried anything after you've started the bike ???

Can anyone send me correct sizes for a decal set. I'm looking to fit the "Hockey stick" type decals to the tank and the small flash and ENDURO 175 logo to the side panels. Sunrise Graphics want a lot of money for the complete set but I have found a graphics company that will manufacture a complete set for £16. I have a photo of the set but need all the sizes, can you help ??? Thanks.

Many thanks, have just sent him an e-mail with picture of what I'm after, hopefully the price won't be to high. If you have the Hockey stick design on the tank and the side panel decals as per your picture I would be interested to know how much they cost, what the quality is like and if you are able to lacquer over the tank decals ???