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Post by dangerousal on Nov 9, 2017 22:20:47 GMT 1
On stripping down my ypvs 350 there was fuel in the right exhaust pipe....I am assuming this is a bad float needle or similar and I had left the tap on prime.....so anyway yesterday I drained the gearbox oil...which was also badly contaminated with fuel...the only path I can think.of for the fuel to take was through the right hand crank seal....does this mean the crank seal has failed....and should I pull the crank and get it rebuilt if the seal has gone then maybe so have the bearings...anyone's thoughts would be gratefully received!
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Post by Tobyjugs on Nov 9, 2017 22:24:00 GMT 1
Wow thats strange,read the last two comments made on the head scratching thread.
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Post by dusty350 on Nov 9, 2017 22:29:21 GMT 1
How weird is that !! Usually a good indication if you can smell fuel in the gearbox oil. Also could be smokier on the right side when running as the engine will pull in and burn gear oil. If crank seals are gone then its an engine strip to change them.
Dusty
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Post by kostas on Nov 9, 2017 22:48:32 GMT 1
Might not be the seal, it may be leaking thru the crankcase parting joint into the gearbox area..
Does not change much as you will still need to split the engine. I would vacuum test it before spliting it.
Kostas
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Post by dangerousal on Nov 9, 2017 23:52:59 GMT 1
So what is the procedure for a crank leak down test please?
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Post by dangerousal on Nov 9, 2017 23:59:16 GMT 1
Lol...never mind I just read the head scratching thread! Leak down test kit? Is there such a thing ? Do you have to do not barrels at the same time?
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Post by kostas on Nov 10, 2017 7:05:55 GMT 1
Leak test kit is available thru a member on here.. not sure who but someone will confirm. Both cylinders at the same time
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Post by dusty350 on Nov 10, 2017 10:29:02 GMT 1
Hi I bought my basic kit through the forum, but it has since been added to, thanks greatly to Yamark I bought the bungs ages ago and never used them. Then when I did my 350lc engine build thread, members asked if I was intending to do a pressure test on the rebuilt engine. Thanks to input on "how to" from other members, and Yamark popping over with his gauge, I did a test on my engine. The kit I have now, again, thanks to Mark, can be used on both Lc and Ypvs engines, and he also made up some adaptors so the coolant circuit can be tested too ; 20171110_085955 by David Miller, on Flickr The blue parts blank off the exhaust ports. The 2 white bungs clamp in your inlet rubbers, the gauge uses one of the adaptors, depending on Lc or pv, to push into the cross over tube port on one side and you blank the other side; 20170315_100644_zpso9haz4yz by David Miller, on Flickr 20170315_100650 by David Miller, on Flickr Make sure you tighten all bolts and clamps. I initially left off the cross over tube clips as they are brand new Yamaha reed block rubbers and felt tight, but the soapy water showed a leak once the system was pressurised. You can see it bubbling on the right side; 20170315_100438_zpsyp5qretb by David Miller, on Flickr You pressure the system up to 6psi and leave it for about 10 mins, looking for a drop in pressure. Any suspect areas are brushed with the soapy water solution which should show any air escaping. I pressurised using a bicycle pump. You are pressurising the cylinders and crank part of the case so it's testing head and base gaskets, crank seals and integrity of the case joints. There are other methods of doing it - the inlet bungs have shraeder valves fitted as standard so you can pressurise through them, but you will need a gauge to measure how much air you introduce, and of course, may be losing. Don't over pressurise as you can damage seals. Mark's gauge came from a plumbers merchants, as did all the fittings Hth Dusty
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Post by dusty350 on Nov 10, 2017 10:57:25 GMT 1
Hi I would add that you can do the test with the engine in the bike. Obviously it will not be possible to brush the seals with soapy water unless you remove everything from the ends of the crank, so do your basic test first. If you get a big drop that you cant find a reason for (top end), then you are going to have to delve further down. Crank seals are designed to keep oil and air out of the combustion chamber, and the fuel mixture in. If petrol is leaking past it into the box then the seal is failing. If one side is U/S, expect the other side to be dodgy too as they are usually fitted as pairs. Has the bike stood for a long time ? When was it last rebuilt ? Were genuine Yam seals used ? Did the builder know what he was doing ? All questions that will help you make a decision on which route to go, but ultimately the pressure test will decide it. And if you do think the seals are the culprit, it's an engine split to change them as they are ribbed, and only use genuine Yamaha - £20 a pair normally. Plus you can check crank and everything else whilst you're at it Dusty
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Post by dangerousal on Apr 4, 2018 9:09:32 GMT 1
Thank you for this extremely thorough explanation and instructions...and apologies that I haven't responded sooner...
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Post by midlifecrisisrd on Apr 4, 2018 14:42:30 GMT 1
Doesn't mean the seals are knackered, just not fuel tight
I've had a couple of bikes that run perfectly well but when the float has stuck open when stored the fuel has filled the crankcase and exhaust and I have noticed weeping fuel out from the lh seal
If it can come out the left it can come out the right and into the gearbox
Also on the last 2 builds I did the source of the leak on the leak down test was actually through the primary gear which was slight and probably not affect the running of the engine but would let fuel through when flooded. (Aircooled motors had an o ring behind it)
Finally, if the engine has been rebuilt before and fuel resistant sealant was not used on the crankcase halves it can dissolve if left in a puddle of petrol
Steve
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phil38
Thrash Merchant
Posts: 426
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Post by phil38 on Apr 4, 2018 15:51:57 GMT 1
Doesn't mean the seals are knackered, just not fuel tight I've had a couple of bikes that run perfectly well but when the float has stuck open when stored the fuel has filled the crankcase and exhaust and I have noticed weeping fuel out from the lh seal If it can come out the left it can come out the right and into the gearbox Also on the last 2 builds I did the source of the leak on the leak down test was actually through the primary gear which was slight and probably not affect the running of the engine but would let fuel through when flooded. (Aircooled motors had an o ring behind it) Finally, if the engine has been rebuilt before and fuel resistant sealant was not used on the crankcase halves it can dissolve if left in a puddle of petrol Steve I'd agree with that. If it runs ok it probably is. The leak down test will probably tell you something but may not and it looks pretty involved!
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Post by dangerousal on Apr 4, 2018 18:18:42 GMT 1
When I tore down the engine it was a bit wierd....some crappy blue silicone had been used but not everywhere...it looked to me like the reason it had been split previously was to replace the output bearing...which had previously spun...and the flywheel which was a very unusual gold colour had been painted...when I pulled it and cleaned it up it had multiple 3 leg puller marks and loads of hammer marks....so someone has had a go who didn't know what they were doing...anyway it's back together and sealed with 3 bond with a new crank...though I haven't started it yet....I suspect it was leaking behind the crank where the silicon seemed very sticky and degraded.
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Post by dusty350 on Apr 4, 2018 18:40:53 GMT 1
A leak down test is pretty straightforward really, and well documented on the forum. Hardest part is getting all the kit, but once you have, you've got it for life. Dusty
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phil38
Thrash Merchant
Posts: 426
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Post by phil38 on Apr 4, 2018 18:43:16 GMT 1
When I tore down the engine it was a bit wierd....some crappy blue silicone had been used but not everywhere...it looked to me like the reason it had been split previously was to replace the output bearing...which had previously spun...and the flywheel which was a very unusual gold colour had been painted...when I pulled it and cleaned it up it had multiple 3 leg puller marks and loads of hammer marks....so someone has had a go who didn't know what they were doing...anyway it's back together and sealed with 3 bond with a new crank...though I haven't started it yet....I suspect it was leaking behind the crank where the silicon seemed very sticky and degraded. I guess that's a good argument for stripping an unknown engine fully before riding off. When I restored my YPVS I was adamant Inwasnt touching the engine, just tidying what was needed and getting it MOT''d. After I did that, first ride out it blew the cap off the header tank. I later found a snapped off head stud with the nut siliconed in! I ended up doing the job properly and found lots of other stuff like sticky rings, worn out PV bushes, output shaft bearing play. Took more time and effort, but I know it's been done properly and less likely to go bang!
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Post by dusty350 on Apr 4, 2018 18:52:01 GMT 1
We never did leak down tests back in the day - more likely we would stick them back together as quickly as we could and get straight back out !! As much as I enjoy building an engine, I don't want to do it regularly as it's too expensive !! I'm not saying a leakdown test is totally fool proof, but once you have the kit it's worth the effort on a new purchase or a rebuilt engine. Dusty
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Post by earthman on Apr 4, 2018 20:24:55 GMT 1
We never did leak down tests back in the day - more likely we would stick them back together as quickly as we could and get straight back out !! Dusty Aye, back then my LC were my daily transport, to get to work etc, couldn't have it off the road for long,...now most of us own something with four wheels and at least another bike at a guess.
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Post by dangerousal on Apr 4, 2018 22:17:30 GMT 1
We never did leak down tests back in the day - more likely we would stick them back together as quickly as we could and get straight back out !! As much as I enjoy building an engine, I don't want to do it regularly as it's too expensive !! I'm not saying a leakdown test is totally fool proof, but once you have the kit it's worth the effort on a new purchase or a rebuilt engine. Dusty yes that's basically the route I've gone...after getting it running I was getting bad clutch slip...on stripping the clutch I discovered the center boss had had one of the pillars repaired with a countesunk bolt from the back of the boss...gear box bearings we're flakey so I stripped completely and have just rebuilt...got it fired up tonight and now sounds tight and responsive...but I think I've buggered my fuel tap
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