OzVMX Forum
Clubroom => Tech Talk => Topic started by: 2T on December 24, 2024, 06:07:15 pm
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Hi all,
I am about to replace my OEM ignition system with an analogue PVL system on an air-cooled 500cc motocrosser (Yamaha WR500).
PVL recommend timing start at 2.2-2.4mm BTDC for open class machines, however standard OEM setting for my bike is 1.7mm BTDC.
Should I set to OEM or PVL measurements?
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Suck it and see. Gazetted settings are good for a starting point though i bet your final settings will have a few adjustments from both those numbers.
You know the process. Choose either , id start with 2.4BTC and give the bike a few runs then try the stock settings with small incremental changes either way to see what the bike likes. Every engine is different and every rider wants something different. Plug chops.
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Thanks for the help pokey.
The bike gets a lot of WOT/high RPM and am a bit concerned about detonation and overheating if going higher than OEM setting.
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Pokey is on the money. The different systems and manufacturers of aftremarket ignitions have different advance and retard values. Some have user programmable advanve/ retard curves. I suggest a softly/softly approach with the testing.
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I love this Forum. :)
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I love this Forum. :)
Me too, I don't know why more people don't contribute with either questions or answers.
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I love this Forum. :)
Me too, I don't know why more people don't contribute with either questions or answers.
It's a shame forums are not as popular as they once were. The good ones have been such a great source of accurate information that's not available elsewhere.
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I love this Forum. :)
Me too, I don't know why more people don't contribute with either questions or answers.
probably because its virtually inactive these days, i used to check it out daily sometimes twice a day, now its every week or 2. as its slow with activity this is the reason not many check it out i reckon.
long gone are the days of the infamouse suzuki footpeg never ending story and the long threads on bikes like the sprite / american eagle / alron saga etc.
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Hoony , just start a thread about to start a CR 500. :)
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Hoony , just start a thread about to start a CR 500. :)
::) yep, that's going to Haunt me forever ;D
in my defense on that Day at Ravenswood Victoria in the middle of winter, when we got to the track there was a thin layer of ice on top of the puddles as they were frozen overnight...very cold indeed.
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You are not the only one , Hoony. I broke at least 3 kickstarter gears on my CR 500 , before I learned to be more gentle. Unlike the 540 KTM , the Honda gears are more fragile.Most of the times we push started the Honda , problem solved. While riding ,keep it singing and have one finger on the clutch leaver ,so you can fang it out of the corner.
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You are not the only one , Hoony. I broke at least 3 kickstarter gears on my CR 500 , before I learned to be more gentle. Unlike the 540 KTM , the Honda gears are more fragile.Most of the times we push started the Honda , problem solved. While riding ,keep it singing and have one finger on the clutch leaver ,so you can fang it out of the corner.
My problem kick starting my CR500 was, splitting the teflon cup in my titanium knee.
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Just had both my knees replaced over the last few months . I will take good care of them from now on. The pain over the last few years has thought me a good lesson.No more kick starting and no more crashing.I just push the starter button from now on , cruise and enjoy the trip.
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And what is the reason for replacing OEM ignition? It was designed and tuned for that motor. PVL, Vape etc are generic ignition systems that can be fitted to many bikes but not always work better than oem. I would use PVL or so if had no other choice. You may end up putin oem ignition back if there is nothing wrong with it.
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And what is the reason for replacing OEM ignition? It was designed and tuned for that motor. PVL, Vape etc are generic ignition systems that can be fitted to many bikes but not always work better than oem. I would use PVL or so if had no other choice. You may end up putin oem ignition back if there is nothing wrong with it.
I have damaging heat related issues. Operating temps (read from temp sensor on spark plug) go up and stay up when bike is used aggressively. Also, temps spike at high rpm. The old OEM ignition is the first thing on my list searching for a cause.
I already had the PVL unit, so no extra outlay just to see if it solves the problem.
I also used the following article from the Rex's-speedshop.com website as a reference (see page three).
https://rexs-speedshop.com/wp-content/uploads/2023/12/Rexs-Capacitor-Discharge-Ignition-Fault-Finding-V2.2.pdf
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id leave the ignition alone. Heat issues are mainly fuel issues and you've said you have fuel issues. Fuel cools the crown so at a very rough guess your a bit lean on the main. Fix the carb issues first so you dont confuse the issue and i wager your heat issues will be no more. As for reading heat try it on the pipe as its far more accurate.
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I've tried the largest main jet available, and the problem persists. Also, I have done a leak down test with no issues evident.
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As you mentioned your problém apears when bike is riden aggressively. I am asuming that ignition works fine under load and higher temperature(aggressive riding). Otherwise you could not ride the bike hard. I would štart with oem jetting and go from there. Once you change main jet than you may need to adjust needl and so on. Please let us know when you fix this issue. Good luck
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Yes, ignition is not showing any signs of being faulty, however I've done so much experimenting with jetting and have seen no reduction or change from the high temps no matter how rich the jetting is. That's why I'm taking another direction and changing the ignition.
Some history of jetting/overheating/piston damage:
I had the bike on a dyno a while back. It had a 190 main jet in it at the time (largest available is 230). Dyno operator was concerned at operating temp and also that temp was jumping up higher. The dyno showed the main was extremely rich. Later that day I took it for a spirited back road blast and pulled up with a piston slap. Temps during that ride were the same as when it was on the dyno. Inspection showed mild detonation on the piston plus slight damage over the front of the piston causing the top ring to stick. The underside of the piston crown also showed it had been too hot.
With a new piston installed I had been working with richer needles and main jets. I had been trying the method of installing a much larger main jet to the point where it would be spluttering when trying to rev the bike out, then gradually moving to leaner jetting until it stopped sputtering, and fine tune from there. Problem was, I couldn't get it to splutter, and the high temps were still occurring at high rpm.
I then tried restricting the airbox and, starting with the richest main available, it would splutter quite a bit. I then changed down through the main jet sizes with the spluttering decreasing as I went, yet high temp problems were still there. I had got down to a 200 main and was about to go further when another problem occurred - Pressure had somehow been building in the gearbox and forced oil out the centre crankcase join and out the clutch cover gasket (see my other thread about spluttering). Investigating that is where I'm at the moment.
The current piston has no evidence of detonation (I'm no expert), but the crown and gudgeon pin have been very hot.
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Should the rabbit hole of cylinder head "Squish" be investigated. I was under the impression all Air Hammers neede work on the head to stop pinging/rattling and jetting issues?
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Should the rabbit hole of cylinder head "Squish" be investigated. I was under the impression all Air Hammers neede work on the head to stop pinging/rattling and jetting issues?
Am using a local mechanic/machinist's version of the common decomp mod but do intend to look at this again if other changes don't solve my problems.
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Any chance that your local mechanic/machinist increased compression ratio while modifiing head. Would this motor benefit from lowering compression ratio a bit?
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Hey Rob, can you post a pic of your head, and list the cc of the head only.
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Any chance that your local mechanic/machinist increased compression ratio while modifiing head. Would this motor benefit from lowering compression ratio a bit?
Pretty sure compression was reduced. Proof is in the ease of starting.
Could it benefit from being reduced more? If that would enable it to cope with mid to top end rpm use with road-going gearing, then yes. I don't know the answer to that though.
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Hi John,
I've never cc'd the head.
Head photo includes an epoxy casting cross-section of the head. Angle of the squish is approximately 28 degrees. Original factory squish angle is (I think) 14.5 degrees. Combustion chamber has not been touched. Let me know if photo isn't visible and I'll try again.
(https://i.postimg.cc/c1D4V1WG/IMG-20250219-122830096-002.jpg)
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Also, squish gap has shown to have no effect on reducing heat issues. Squish gap was 1.65mm when original issues showed, and I have been running 1.2mm since then with similar issues.
Having said that, although the heat issues are still there, I haven't had the detonation damage to the piston with the tighter squish gap.
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I take it you havnt cleaned up that head and its showing quite a lot of burnt oil on the EX side and that's all. You also mention the heat and you mention you HAD Det issues before changing the squish. Difficulty in jetting ….. All those points lead to a bad seal even though you have mentioned a leak down test. The gearbox issue also mentioned adds to the air leak argument being the root cause despite the leak down test. Nothing else will cause all those issues apart from an air leak. Changing to a lower octane fuel can have results but that's only done after the jetting is correct and its not plus it could mask other symptoms. Swapping out the ignition wont do much unless its faulty. If it was my engine Id have the engine pulled down on the bench and reseal the centre gasket and throw a new pair of good quality seals in so I knew it was good before trying anything more in the top end or electrical. best of luck with it.
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Good pics Rob, thanks. You say the "squish angle is 28 degrees", what is the angle of the piston crown? I'm thinking that if the 'head squish angle' does not match the piston crown angle closely ( I think an increase in clearance of .5mm towards the centre of the bore, is good), the benefits of 'squish' would not be realized?
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The piston crown angle is approximately 11 degrees.
Geez that's a good point you make, John. With the squish angle being so large it borders on eliminating it as a squish and becoming an extension of the combustion chamber. Would this be enough to cause such high operating temperatures?
Also, along with all my other problems, blown head gaskets have been an issue. This could be the cause.
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Yes "With the squish angle being so large it borders on eliminating it as a squish", squish helps cooling by not exposing so much of the cylinder-head during combustion.
This site has some things to consider ....https://kdxrider.net/forums/viewtopic.php?t=26022
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Well, it's a bit of a relief to now have a direction to head in, rather than flying blind. I have two other heads, so will see which is suitable for use.
The motor is fully disassembled atm after checking integrity of crankcase join seal and testing for cracks in crankcases that may have been opening up at high temp and letting pressure into the gearbox. Both were fine so will work at getting it back together. Have never assembled a bottom end or installed an ignition, so that should be interesting.
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Pokey, regarding your last post mentioning the possibility of an air leak, even though the leak down test was fine.
I have just been reading an article on http://kenoconnorracing.com/ The article is http://kenoconnorracing.com/vacuum-leaks.php
He mentions oil coming out of the gearbox breather as a symptom of a clutch side crank seal leak or a crankcase leak between the crank and gearbox. I had had oil coming out the breather a few times before it started leaking from the seals.
My crank seals are only eleven hours old, and I wasn't going to bother replacing them, but I will now. Will also concentrate on getting a good seal between the two crankcase halves. Oil was leaking from just behind the cylinder, right near the breather outlet, so it may have been travelling from the crankcase through to the gearbox.
Thanks for the tip!
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Fingers crossed you get to the heart of the issue. One other place that air cooled big bores have leak issues is the base gasket Im sure i read on this site where a CR500 was literally eating them. I dont recall the fix for it but it is an area to also look at.
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Needing some advice.
While prepping to reassemble my bottom end I removed the clutch side crank seal, and it came out pretty easy.
I can push it back into place by hand.
Should I be concerned?
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Looks like you found the smoking gun. Grab the verniers and measure to ensure the seal is actually to spec and the cases. Same as fork seals , if you soak them for an hour in oil they will soften and swell a bit but a better idea is a sealant. I use Hylomar though Yamabond should work okay or you could go via one of the Loctite products like 648 retaining compound. You local bearing shop should have what you need so have a chat with them.
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Diameter of both the old and new seal are approximately .6mm larger than the crankcase. Mating surface is a little rough but does not look worn.
Will fit the new seal and do another leak down test when it is all assembled.
Looking at the workshop manual there's not a single mention of crank seals. Seems a bit strange.
forkin' bikes. >:(
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0.6mm "should" be okay if you use a sealant to stop the seal from walking and they do and can give erroneous readings. When testing remember no more that 8 PSI, any more and your causing problems as your over charging.
The working differential pressure tween the case and the created low pressure in the combustion chamber that rises the charge to the combustion chamber is much less like 4-6PSI unless its hyper charged like snowmobiles with superchargers or turbos. The expansion chamber reflection wave scavenging sucks a lot higher PSI though its effect is reduces the further its length. Once you get the bottom end solid you can think about the top end carburation exhaust and squish but it all starts with the bottom end being rock solid and without that your confusing errors.
I work mostly with small bores and a wipe with Hylomar on all sealing surfaces is my go to if it needs it or not and has never caused me to double think and i rarely test bottom ends though you shouldnt be able to just push a seal in raw with your fingers and expect it to hold up at RPM.
Fairly obvious your sucking air and gearbox lube which points directly to the RH seal (or centre gasket/sealant) and you mentioned a rough surface on the seal journal which i cant comment on how it occurred but I have suggested a possible go around with a sealant. Unsure how that happened as the japs are pretty good with machining though a shim loctited in the journal could be the answer if you feel the journal is beyond spec with its imperfections. One for you and you machine shop.
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As I mentioned, the sealing surface was a bit rough. It also had dark marks showing the notches where, at some stage, it had been running with a seal in backwards. :o
I have since given it a clean with a scotchbrite pad and except for a light gouge (probably from a screwdriver removing a previous seal), it is looking really good.
Will be fitting the new seal tomorrow and hopefully it's a bit tighter than the one I've just removed. Was thinking although it's not as tight a fit as I might like, any sealant will still probably just get pushed off as it goes in. It might seal the screwdriver gouge though.
As to whether the seal has actually been leaking is a mystery. I thought a seal leak sucked oil in, yet it wasn't belching smoke, and I had pressure in the gearbox. I'm hoping it's not a seal problem because the existing seal was only 11 hours old. I'm thinking why should the new one be any better and if it leaks again what then? Source another slightly bigger seal? Hopefully not insert a shim.
When I disassembled the bottom end, it was hard to tell if the crankcase join had been sealed correctly. All I can do is make sure I get it right when I do it. Apart from oozing out the clutch cover gasket, oil was also coming out the join right above the gearbox breather, about an inch behind the barrel/crankcase join. Is that a sign it may have been coming through from the crank cavity? I don't know.
Also, regarding seal 'walking'. What do you mean, pokey?
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Walking is a reference to seals or bearings moving along the shaft if not secured. An alternative to a shim is epoxy.
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Seal is in (with a bit of surface prep and a wipe of Threebond). Used a large socket to guide it but didn't need any extra force to get it in.
Regarding crankcase assembly, is it ok to gradually tighten the case bolts to force the case onto the crank or is a crankshaft installing tool the best method?
(https://i.postimg.cc/rFxZNp74/IMG-20250301-104932765-002.jpg)
(https://i.postimg.cc/T1m00kNx/IMG-20250301-110743490-002.jpg)
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helo
clutch side should go in first. use some sort of puller/pusher that is pushing on inner race to get the crankshaft in. it is not the best idea to put pressure on bearing balls(side load). once crank shaft is installed in clutch side case use the same method to install ignition side. i usually install oil seals last when engine cases are bolted together. it is easy to tap them in with socket or if you have a special tool for installing oil seal you can use that. if you try to pull cases together using case bolts you may find that crankshaft will be tight. you should be able to spin correctly installed crankshaft by two fingers(no seals installed). good luck
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Hi Tomas,
Watching a youtube video of an older yz490 motor assembly (mine is the same as the later '87-'90 motor), it seems a crank installer tool can't be used for the clutch side. The guy just applied a small amount of heat to the bearing and the crank slipped in very easily.
I haven't installed the stator side seal yet and expect if I do it after joining the crankcases I'll need a pipe or tube to fit over the shaft to push the seal into place. The guy in the video used a crank installation tool to push the crankcases together with the seal already in place.
It seemed to work well.
As you mentioned about using case bolts to pull cases together, yes, that doesn't seem ideal. I think I'll be able to borrow an installation tool to do that job.
Thanks for your advice.
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I just tap the seals in with a hammer, if they don't slip in with a finger push, never had an issue in 50 years :-)
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I like your simple approach, John. I procrastinate way too much.
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I just tap the seals in with a hammer, if they don't slip in with a finger push, never had an issue in 50 years :-)
yep i have been doing same for nearly as long, a soft faced hammer and gentle taps does the trick.