PVL Timing

[2T]

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.

[2T]

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!

[pokey]

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.

[2T]

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?

[pokey]

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.

[2T]

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.

[pokey]

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.

[2T]

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.

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?

[pokey]

Walking is a reference to seals or bearings moving along the shaft if not secured. An alternative to a shim is epoxy.

[2T]

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?

[Tomas]

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

[2T]

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.

[John Orchard]

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 :-)

[2T]

I like your simple approach, John. I procrastinate way too much.

[Hoony]

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.