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Post by Header on Oct 21, 2019 13:50:21 GMT 1
www.flickr.com/photos/183837880@N04/48935595476/in/dateposted-public/www.flickr.com/photos/183837880@N04/48935506601/in/dateposted-public/folks looks like im in trouble again, bike has 500 miles on complete rebuild motor,crank,pistons the lot,carbs,wiring the lot,all new carb kits,new coils,pretty much every thing was done to the bike timing was set correctly,carbs running 240 mains,standard plugs,standard airbox,micron full system like new, what caused this to go,air mixture set normal both sides, was running sweet,took her for a 50 mile spin heavy rain and going up hill in 4th at 65mph she locked the back wheel for split second i pulled the clutch quickly and shut her down,still kicking with plenty of compression,the whole motor was fully rebuilt.left hand side plug seems perfect.
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Post by Header on Oct 21, 2019 13:52:39 GMT 1
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Post by abar121 on Oct 21, 2019 14:29:51 GMT 1
Oh no, sorry to hear.
I would do a leak down test when you have it back together.
Also were they genuine jets? Japanese pistons?
Cheers.
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Post by Header on Oct 21, 2019 14:35:47 GMT 1
Oh no, sorry to hear. I would do a leak down test when you have it back together. Also were they genuine jets? Japanese pistons? Cheers. all parts were from Norbo here,mitaka pistons,240 jets off here also,all new rubbers,engine has only 500 miles correctly run in,standard air box
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Post by ianboom on Oct 21, 2019 14:49:02 GMT 1
That looks like it has been running really weak and the piston has started to melt. Have you checked the float height in the carb? May be worth removing the pipe and looking up the exhaust port to see what the top of the piston looks like.
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Post by russpuss on Oct 21, 2019 20:15:43 GMT 1
I had this happen on my X7, turned out that I'd run it for a couple of hundred miles then should have torqued the head back down, I didn't and it leaked and blew.
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Post by Yogi on Oct 21, 2019 20:25:38 GMT 1
Might help get more replies if the pics up Matt
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Post by hoist1 on Oct 21, 2019 20:45:39 GMT 1
Are the plugs 8s ? Offending plug washer doesn’t look very compressed, was it tight enough?
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Post by tacky1 on Oct 21, 2019 21:19:06 GMT 1
Are the plugs 8s ? Offending plug washer doesn’t look very compressed, was it tight enough? Well spotted, That could be the problem right there
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Post by steeley on Oct 22, 2019 6:47:52 GMT 1
Oh no, sorry to hear. I would do a leak down test when you have it back together. Also were they genuine jets? Japanese pistons? Cheers. Had that happen some years ago . Turned out to be a wrong size main jet in the one carb .So it was a simple fix . New piston cleaned cylinder up by scraping smeared ali off cylinder wall and gave it a whizz round with some p120 and washed it out and built it back up. I would make sure the head is flat, also check that the base gaskets are not over lapped.
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Post by hoist1 on Oct 22, 2019 7:25:11 GMT 1
Could be so many things, 2 strokes are a bit like carbs, very simple but can be sensitive to small differences. Do whatever needs doing to that cylinder and get the bike on a dyno .
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Post by Header on Oct 22, 2019 8:53:18 GMT 1
www.flickr.com/photos/183837880@N04/48940488306/in/dateposted-public/www.flickr.com/photos/183837880@N04/48940678157/in/dateposted-public/update folks, pulled the piston last night it was well shot,but didnt break up, crank looks good, still no closer to why it happened, they are mitaka pistons 2mm over from Norbo, new inlet rubbers new reeds, 240 main jets standard pilots all new and clear carbs had full rebuild kits from norbo new plugs b8es new headgasket from Norbo, full system microns new also,new standard airbox and filter, Brand new crank from norbo probably 500 miles on it since complete rebuild with new crank seals the lot, folks this bike is mint in every way we are baffled to why this happened,we were not in band when back wheel locked but she did free herself just as quick,so was lucky the way the piston went no debri down the crank,as for jetting the left side piston looks perfect,some say the r/h side plug was loose as the washer was not squeezed, we spent hours last night and still no closer to why this happened
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Post by headcoats on Oct 22, 2019 9:19:29 GMT 1
Intake leak around the inlet manifolds ?
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Post by midlifecrisisrd on Oct 22, 2019 9:45:56 GMT 1
You need to build it back up and do 2 things
1 - pressure check it for leaks. As you say left looks fine so something is wrong on the right
2 - check when left is on BDC that the right is on TDC and vice versa. A twist in the crank will throw out the timing on the right
Also with microns the partial throttle midrange is the usual problem spot for them. Usually rich causing a stutter but yours may be lean there.
Check the other 2 points first as there is deffo a difference between those cylinders
Steve
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Post by hoist1 on Oct 22, 2019 11:12:02 GMT 1
Just running through a few things, the last piston I saw like that ( rd 350b ) the bike was going down a big hill ! Not sure if going up one is more likely to cause this but I did hole a piston on a Honda cbx 750 on the m1 up a long uphill drag at high speed 2 up , I replaced the piston and had no further trouble but there was nothing to be found as to the cause. Assuming your right hand carb is delivering identical to the left at the main jet, either float height or tap flow bias related, though the other side is ok could it have happened the other side if it hadn’t done this first. Could it need more miles on ? So 4th gear at 65 but out the power ?
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Post by reedpete on Oct 22, 2019 14:18:17 GMT 1
To collect particles on the plug tip like that is symptomatic of pre ignition... I appreciate its only done it on one side but few things jump out at me ...you are using B8ES....I’ve never run less than a 9, and 10s in hot summer. Also as you are on 66mm bore , have you reset combustion volume or squish? Compression ratio will be on or past the limit with std. fuel and std. ignition timing if you have same head volume as stock. It’s effected a 375cc engine running ‘high’ compression...not that surprised it might turn a B8ES into a glow plug !
small differences, minor leaks might push things over the edge on one side. If a plug overheats then it’s a run away situation as it just gets hotter and hotter as the preignition develops.
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Post by Header on Oct 22, 2019 14:51:12 GMT 1
To collect particles on the plug tip like that is symptomatic of pre ignition... I appreciate its only done it on one side but few things jump out at me ...you are using B8ES....I’ve never run less than a 9, and 10s in hot summer. Also as you are on 66mm bore , have you reset combustion volume or squish? Compression ratio will be on or past the limit with std. fuel and std. ignition timing if you have same head volume as stock. It’s effected a 375cc engine running ‘high’ compression...not that surprised it might turn a B8ES into a glow plug ! small differences, minor leaks might push things over the edge on one side. If a plug overheats then it’s a run away situation as it just gets hotter and hotter as the preignition develops. it was not in the band, few miles before this it spluttered and was down on power,i reckon it was the start of it, i have new piston on the way will put dial guage on crank will probably set timing to 1.8 tdc as its got more cc than standard, will run competition plugs which im told are better,will come up a size or 2 on main jets
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Post by midlifecrisisrd on Oct 22, 2019 14:58:29 GMT 1
I'd message 4l04ever and get a slightly thicker base gasket to play safe on squish/head volume with the 66mm bore
Steve
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Post by reedpete on Oct 22, 2019 15:19:39 GMT 1
To collect particles on the plug tip like that is symptomatic of pre ignition... I appreciate its only done it on one side but few things jump out at me ...you are using B8ES....I’ve never run less than a 9, and 10s in hot summer. Also as you are on 66mm bore , have you reset combustion volume or squish? Compression ratio will be on or past the limit with std. fuel and std. ignition timing if you have same head volume as stock. It’s effected a 375cc engine running ‘high’ compression...not that surprised it might turn a B8ES into a glow plug ! small differences, minor leaks might push things over the edge on one side. If a plug overheats then it’s a run away situation as it just gets hotter and hotter as the preignition develops. it was not in the band, few miles before this it spluttered and was down on power,i reckon it was the start of it, i have new piston on the way will put dial guage on crank will probably set timing to 1.8 tdc as its got more cc than standard, will run competition plugs which im told are better,will come up a size or 2 on main jets Quite possibly found the lean conditions off the power, but everything you now said is making sense. Essentially without adjustments 66m bore on std. timing and tolerance, 8 plugs , stock head profile ....defo recipe for unhappiness! as steve said raise the barrels a tad with a thicker base gasket is minimal solution but large squish can take you to good conditions for detonation, so ideally you need a little volume added to the chamber. Also be mindful of what fuel you are putting in it...regular 95 pump petrol formulation is getting worse and worse for a LCs needs. Nothing wrong is going safety rich on the main jet but don’t just assume that means anything without some WOT plug chops or ideally a little Dyno time.
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Post by cb250g5 on Oct 22, 2019 16:16:00 GMT 1
What pipes are you on? If that's the front of the piston, I'd check you don't have a partial blockage of the exhaust pipe on that side.
I did a pair of pistons like that, due to too small stingers.
As you have 1 good side, I'd be looking for a fault, rather than a set-up issue that would affect both sides.
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Post by Header on Oct 22, 2019 16:21:04 GMT 1
What pipes are you on? If that's the front of the piston, I'd check you don't have a partial blockage of the exhaust pipe on that side. I did a pair of pistons like that, due to too small stingers. As you have 1 good side, I'd be looking for a fault, rather than a set-up issue that would affect both sides. full set of microns like new but will check for blockage later this evening, what plugs do u think ?,and will i go up on main jets have 240 now have new 250s and 260s at home ,will i time her to less than 2mm ?
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Post by tsa on Oct 22, 2019 16:40:14 GMT 1
Only buy genuine main jets too as some pattern ones do not flow as much fuel even though they have the same number on.
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Post by marrcel on Oct 22, 2019 18:07:54 GMT 1
When you did 65mph in 4th how much throttle did you have? My pv pistons melted at 1/4 open throttle. 3clip on the needle was to lean for my setup.
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Post by jon on Oct 22, 2019 18:08:45 GMT 1
Are the plugs 8s ? Offending plug washer doesn’t look very compressed, was it tight enough? +1 When I recently built my YPVS engine, I just nipped the plugs up during rebuild so as not to crush the washers as I was going to do a squish band clearance when I got some solder. Just wanted to stop debris entering before I got round to it. Did a leak down test in between, and lost pressure very quickly. Soapy water showed it was leaking from the plugs. After the squish test and tightening to the correct torque there were no leaks. That’s not to say as others have suggested it’s the only problem. Jon
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Post by reedpete on Oct 22, 2019 19:03:19 GMT 1
What pipes are you on? If that's the front of the piston, I'd check you don't have a partial blockage of the exhaust pipe on that side. I did a pair of pistons like that, due to too small stingers. As you have 1 good side, I'd be looking for a fault, rather than a set-up issue that would affect both sides. Don’t think you can say there is a ‘good’ side...all you can say is that one side melted first . Unconstrained preignition will result in thermal runway on the first affected side. there will be enough variance in setup on this motor given it hasn’t been blue printed that one side is bound to have more compression, run leaner etc..the dominant effect will have just done that side first. but for sure, running 2.0 of timing, nominal jetting on 375cc with microns is a recipe for trouble. there are those with much more setup experience than me on here but I’d be running timing at 1.7mm, squish set to 0.9, 9 or 10 heat ratting plugs. CR is going to be high but what action depends on fuel you want to generally use etc.
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Post by Header on Oct 23, 2019 13:53:27 GMT 1
update folks, looks like a skimmed head,and motor ported savage power in band, bored to 66mm, so wrong timing at 2mm btdc should be 1.8mm, wrong plugs using be8 should be 9s,240 main jets should be 260 or more all this together is the issue i am being told
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Post by tacky1 on Oct 24, 2019 1:12:10 GMT 1
I dunno, I run B8s in mine and 2mm timing and it is heavily ported and machined down head, 28mm carbs and it runs friggin class, right into the red in every gear... Did you look at what Hoist1 pointed out about the plug in the earlier picture, That blown plug doesn't look like it was tightened and that would definitely do the damage that happened, Massive air leak!!!
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Post by Header on Oct 24, 2019 11:47:21 GMT 1
I dunno, I run B8s in mine and 2mm timing and it is heavily ported and machined down head, 28mm carbs and it runs friggin class, right into the red in every gear... Did you look at what Hoist1 pointed out about the plug in the earlier picture, That blown plug doesn't look like it was tightened and that would definitely do the damage that happened, Massive air leak!!! we are defo thinking the plug was not down fully as the washer was not closed at all
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Post by hoist1 on Oct 25, 2019 19:48:15 GMT 1
I dunno, I run B8s in mine and 2mm timing and it is heavily ported and machined down head, 28mm carbs and it runs friggin class, right into the red in every gear... Did you look at what Hoist1 pointed out about the plug in the earlier picture, That blown plug doesn't look like it was tightened and that would definitely do the damage that happened, Massive air leak!!! we are defo thinking the plug was not down fully as the washer was not closed at all I didn’t like to also point out that the tight one was over tightened , I hadn’t seen other pics but now I have it’s looking like many things had a bearing. Still wondered if the bores wanted a bit more bedding in, its not so much the mileage but the progression of working it a bit more. Rightly or wrongly a mate would run his rd’s in by what he called thrashing them in, it seemed to work for him.thanks tacky and header.
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Post by 4l04ever on Oct 26, 2019 17:15:05 GMT 1
If you have the TUV approved Microns, the cans are very restrictive as they have a baffle plate inside. These can cause issues. You could replace them with Tyga cans or other free flowing cans, with a large enough ID to allow the gases to get out.
Measure squish and volumes if the head has been skimmed. The squish may be okay, but the volume may be too small.
Do a leak down test when rebuilding.
I have Siamese base gaskets available too, so you cannot get an overlap then.
Good luck!
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