RM400N Oil in Crank...Help!!!

[Toolboy]

Gday all,

A few months ago and apparently for no known reason my RM400N started fouling plugs, so i replaced the crankseal and o ring, pieced the bike back together it still fouled.

Last week i split the engine and replaced the crankcase gasket. Whislt apart i could not see where to gasket was at fault with the cases??

The bike seemed to run fine once assembled and was pushed pretty hard at Connondale on the weekend.

Today i have taken off the barrel to have a look inside and here are the pic:

Everything looks fine


Rotate the crank:



The top of the piston:


Breather holes in crankcases:



It defiently looks like the  left breather holes is where the oil is coming from

Any help or suggestions??

Tim

 

[Doc]

Perfectly normal Tim. The oil holes are for lubrication of the main bearings, some engines only have the hole on the left as the right side is lubed by the tranny oil. The oil at the bottom of the cases is residue from the mix. There is even a special tech name for this residual oil but it eludes me at present. Might look like gearbox oil but it isn't

[vmx42]

I am at a loss to explain how it could come from the left [ignition] side breather as there is no possible access to the gearbox oil from that side.

But, I had a faulty petcock once. There was a small amount of fuel left in the tank and the slow leak eventually partially filled the crankcases. The fuel evaporated and left behind a pool of pre-mix oil. It wasn't that dissimilar to what you have described.

[Doc]

on a side note, 1 thing to be wary of when reassembling any old Suzuki 2 smoker is the over use of the black aviation type gasket goo. It's preferable not to use a sealant at all. If you do need to use anything then go for a thin smear of silicon type sealer. You'll find if the gasket and mating surfaces are good then all you'll need is to smear the gasket with oil and assemble it like that. The oil swells the gasket and should not leak. This includes crankcase gasket, base gasket, reed gasket and clutch cover gasket. Have seen motors wrecked from over use of gasket sealant, especially the the gooey black type  

[SLAWESY]

You haven't started running 100 octane have you, that may make it run rich and foul plugs... Not advice from an expert but it did happen to me on my 250.. leaned out main jet and now is all ok.

[Mike52]

We've had this one before I think.
All two strokes have oil floating around in the crankcase.
Nature of the beast.
Put it back together and ride it.

[Hardo]

I recently restored a PE250 Z (82 model) which had the EXACT same symptoms.

It wasn't "good" fuel lubrication in my case - it was ever so slightly drawing it from between the case halves out of the gearbox and fouling plugs instantly.

My fix: I split the cases, lightly and ever-so-gently "decked" the case halves on a large sheet of flat wet and dry (and found them to actually be not quite true and level!!) replaced the centre gasket, with the smallest smear of yamabond, whacked it all back together and it fixed the issue.

I know you said you had it split before, but in my recent experiences you just may need to do what I did mate.

Hope that helps.....  Bloody Suzuki's hey.... 
Hardo

[Doc]

What bothers me a little in the photo's of the crank is how the top halves of the crank look so dry after the bike had only been ridden a couple of days ago. Hopefully you may have simply wiped the crank with a rag and then spun it which then picked up the oil from the bottom of cases. The cases where the oil feed holes are look to be coated with an oil film so I'm assuming you probably wiped around the crank/rod area. It isn't overly common to have the cases draw tranny oil but not saying it doesn't happen as Hardo pointed out with his recent experience. Yamabond or Threebond sealers are fine but as a general rule..less is best. I don't remember ever pulling apart any early Suzuki engine to find gasket sealant used from the factory. (excepting engines where no centre case gaskets are fitted)

[Graeme M]

There should indeed be a little oil on the floor of the cases if it's all running right, however in this case two things stand out to me (tho I am no expert).

1. The oil in the pic is dirty. Typically the residue I see in my engines is pretty clean.
2. There seems to be some scoring on the piston.

Now, I don't know quite what to make of that and perhaps I'm just imagining things. Any thoughts? I like the sound of Hardo's suggestion.

[Mike52]

Gday all,
The bike seemed to run fine once assembled and was pushed pretty hard at Connondale on the weekend.
Today i have taken off the barrel to have a look inside and here are the pic:
Rotate the crank:


The top of the piston:


Any help or suggestions??
Tim
 

How I read it " had a problem , split cases ,new gasket , ran good at connondale, took top off and this is what I found".
No mention of plug fouling now.
No mention of any problem except the oil which is normal.
Other than the piston/bore coming to it's use by date I'me sorry but I can't see the problem.

[Doc]

My thoughts on the dark amber colour of the oil maybe due to the gasket goo washing off around the reed valve area or in the actual cases surrounding the crank. I'm a little fussy in this regard but I've always kept the internals of my engines and air filter scrupulously (almost surgically) clean. If infact there is any grit in the residue pictured I'd be looking at my air filter as the major probable source. There does appear some scuffing to the piston as Graeme noticed and the lower edge does indicate some piston rock. If the bore/ring is getting a little worn the drop in compression could also lead to the fuel mixture not burning as cleanly as it should thus leaving slightly increased oil deposits. Coulda woulda shoulda..could be a number of things that can't really be 'measured' by pictures alone, if the bike was going well, ring gap is fine (hard to see if there is any blow by under the ring) if everything else seemed normal I'd leave well and good enough alone excepting the air filter which should be cleaned regularly. Removing the top end off to simply inspect 'too often' can cause it's own issues with head studs and such pulling. Waiting for Lozza comments

[Lozza]

There is not a quality oil being used (the 'striations' Ithink they are called) or lots of verticle lines left on the piston, your jetting is to lean your on the very edge of a seizure(grey death ash and the pock marks).
RM 400 pistons(PE as well) suffer badly from excess expansion on all 4 'corners', right where the cutaway is. Happens on stock and aftermarket pistons

[pmc57]

I'd agree that there may be some issue with the centre case gasket surfaces, also is it possible the right hank crank seal is in the wrong way around? These seals are double lipped and will seal either way around but maybe it's let some oil from the transmission to pass if in the wrong way. Also inspect the seal area on the crank itself, may be some imperfections.
Good to see Doc's back.

[LWC82PE]

I always assemble the center gaskets with Threebond grey 1215, Loctite 515 for base (sometimes Threebond though) and Hylomar/Aero blue for the head gasket (unless it is the type where the manufacture says to use no sealant).Threebond is what the Japanese factories use and i have never had a problem with it. I can not afford rebuild an engine and then have to tear it down again because of a leak so the Threebond is piece of mind. The whole idea is to not use heaps of it so you block up oil galleries or whatever, i have pulled apart many engines that have be stuck together with way too much sealant by other people. It is very rare you pull apart an old engine that has got perfect gasket surfaces. Theres always little nicks etc.

[smed]

When i pull my 2t bikes top ends off there is always oil on the crank,the fuel evaporates & leaves the oil behind,the oil I use is blue so its easily identifiable,what brand & colour oil do you use & what ratio?
If its the same as whats on your crank then thats all it is,If that is the oil you are using then i agree with lozza it looks like a  crappy brand of oil