Oily spark plugs?

[jono035]

My GSX250F Across (inline 4 cyl 250cc 4stroke) has been running a little rough, sounds kind of like it has a mild misfire when idling and doesn't feel like it is running cleanly while cruising. It seems like it might be misfiring or something but I'm only used to working on car engines where I guess a misfire is more pronounced due to lower revs?

Anyway, I warmed up the engine, let it run for a bit then pulled the plugs and found oil all over the electrodes...

Thats pretty much rings or valve stem seals, right?

There was also a little bit of oil in the air filter housing (where the rocker cover breather feeds to) when I pulled that to bits a couple of weeks ago, but there aren't any oil spots under where I park the bike so I don't think there has been much pushed out the breather...

Also does anyone have any advice or tips and tricks for pulling the head off a bike engine? Is there anything else I should be checking with the head off? (service manual mentions valve stem runout etc.) Any tools that are an absolute requirement as I only have a socket set and spanners at the moment?

Also does anyone know if it is possible to get non-genuine rebuild pars (rings/gaskets/seals) for older suzuki bikes? When I priced up a few replacement pieces for the carbs just in case there were a few things (like the diaphragm at $450 each) that were prohibitively expensive...

The other thing of course is that with some cars people recommend using a heavier weight of oil in an engine once it has past a 100k or so, anyone have an opinion on this with bikes? I'd rather fix the problem but if the cost of rings/gaskets comes out at half the value of the bike then it may not be practical...

[NOWOOL]

You don't mention the mileage on your bike or the last time the valves were adjusted which would help....if the mileage is low and unless the bike has been abused i'd side with it being the valves rather than the rings..........for pulling the head off; that's a major job and if you are game then go by the shop manual which you can find here or have a shop do it......its more important that it be put on properly and tighten up after 600 or so kms. Yeah, you don't have even the right tools to adjust the valves so i'd have it done for you. once its off you could check for signs of excessive heat but if the bike is over 100,000 kms then you might as well have it rebuilt.
the cost may be relatively high but at least the engine should be trouble free for 50,000 kms.

[jono035]

Yeah sorry, age and kms was an oversight...

It is a 1991 bike with 60k on the clock, couldn't find out from the guy who I bought it off whether it had ever been rebuilt or anything, but he had only had it for a year and done a few thousand km on it... Valves I have no idea about at all but that is the main reason I started pulling it to bits, figure why stop there... The bike isn't exactly in top condition and I'd guess it's been pretty well abused...

I'm up for the challenge of pulling the head off, done that with a few cars before but that was a fair few years ago and never a bike so the more info I can sponge up before hand, the better...

Some tools I don't mind getting... The tappet clearance procedure appears to be a case of getting a feeler gauge and the correct shims, right? Or is valve adjustment a different procedure to that?

Anything major and I will just take the parts in to a shop... Any idea what the normal set of procedures for a bike engine is? Cylinders re-bored, head planed? Would it be worth pulling the crankshaft out and checking/replacing the bearings?

[awayatc]

Anything major and I will just take the parts in to a shop... Any idea what the normal set of procedures for a bike engine is? Cylinders re-bored, head planed? Would it be worth pulling the crankshaft out and checking/replacing the bearings?

Or work out how much bike is worth now.....
How much do you need to pay for one that is up to specs....
How much will you need to spend in parts (A lot more expensive then car parts)

And estimate how many hours you will need to spend on rebuild.....
Not everybodys cuppa tea to rebuild engines.....
If you enjoy it go for it, but allow for 4x as much time as estimated,
and 2x the cost


Then decide wether it is worth the effort, or you may work those hours earning some coin to upgrade lateron....

(you can with compressiontesting figure out if it is rings or valvestem seals...
pour bit oil in bores to see if that improves compression=rings)

[CookMySock]

Strip and clean. Buy oversize pistons/rings and have block bored out to suit. Replace con rod bearings, check all others. Send head for professional checkover and/or rebuild. Visual check over everything - replace where worn or scored. Replace all gaskets and any perished rubber.

Assemble and run it in.

Steve

[jono035]

Yeah, this plan is still pretty dependent on what the parts work out to be as the only other engines I've stripped down have had commonly available generic parts. As for the time input, a lot of it is an out-of-interest project, so I can stand sinking a bit more time into it than I would otherwise. Also I'm going to be going back to Uni in a month so need the bike to be reliable for commuting but don't want to spend too much given that it may turn out that I upgrade once I'm onto my full anyway.

That compression test trick is an interesting one awayatc, would be doing a compression test on each cylinder before I pull it down anyway, so I'll dump a little oil in and see what happens...

DB - Yep, thats the idea although I've got no problems doing minor valve and seat repair with a bit of grinding paste (assuming that is appropriate) so between that and valve guide/seal replacement and possibly a head plane is there anything else that a professional head-rebuild will cover?

I'm not looking for perfection, just improvement really...

[CookMySock]

I've got no problems doing minor valve and seat repair with a bit of grinding paste (assuming that is appropriate) so between that and valve guide/seal replacement and possibly a head plane is there anything else that a professional head-rebuild will cover? I'm not looking for perfection, just improvement really...

If you just want to tidy it up, by all means pull it apart and fix only what's necessary.

Yeah if the valve guides need replacing you will need professional assistance. You might want to get it crack tested too.

Steve

[jono035]

Crack test would be a good idea, will see what the overall condition of the head is and how it compression tests first I guess...

Valve guides are a question mark, haven't done that before and it looks too specialist to try so that would definitely be a job for a pro...

awayatc - with the oil-in-the-bore and compression test trick, does that need to have the engine oriented so the piston heads are horizontal (so the oil pools around the edge of the piston?) and would that show anything given that there already appears to be a little bit of oil in the bore (wetting the plugs while running)?

Anyone know a good place to get any of this done within Auckland? Is a motorcycle place a requirement or can any engine rebuild shop be used?

[awayatc]

Do compression test as per usual...mark down the numbers.
Poor down a bit of oil down each bore, and test immediately after....this will improve your seal if rings are worn , and your compression figures should be noticably higher with the oil in bore.
If compression remains similar, then you are lucky and only the valve stem seals are most likely shot....

Good luck

[xwhatsit]

Hang on, before you start pricing up pistons and valves and oil seals...

So far there's just a misfire and oil on the plugs. Does the exhaust smoke at all? What about once you start it up once you've left it overnight? Or does it smoke when under load (get somebody to ride behind you).

More importantly, once you've cleaned the plugs (or put new ones in), does the misfire/odd behaviour go away? If it does go away, how long does it stay good before it turns to crap again (pull the plugs again and see how it looks).

[jono035]

Thanks awayatc!

I just looked in the service manual and it doesn't mention anything about valve stem seals, only that you install oversized valve guides and then ream them, so I guess the guides provide the seal... In that case it may not be much difference whether it is rings or valve guides... or both...

[T.W.R]

Do compression test as per usual...mark down the numbers.
Poor down a bit of oil down each bore, and test immediately after....this will improve your seal if rings are worn , and your compression figures should be noticably higher with the oil in bore.
If compression remains similar, then you are lucky and only the valve stem seals are most likely shot....

Good luck

Uh huh a little bit of knowledge is dangerous there are plenty more variables to be taken into consideration.

[jono035]

Hang on, before you start pricing up pistons and valves and oil seals...

So far there's just a misfire and oil on the plugs. Does the exhaust smoke at all? What about once you start it up once you've left it overnight? Or does it smoke when under load (get somebody to ride behind you).

More importantly, once you've cleaned the plugs (or put new ones in), does the misfire/odd behaviour go away? If it does go away, how long does it stay good before it turns to crap again (pull the plugs again and see how it looks).

I 'think' it's a bit of a misfire, doesn't sound like it compared to cars I've diagnosed, but then with higher RPM I guess a misfire is less critical...

The plugs are surprisingly clean apart from the oil, no carbon built up, but I guess they've been getting washed by the oil. Cleaned the oil off the plugs, put them back in, ran the bike until warm then for about 20-30s at 7k rpm, shut it off and pulled the plugs, more oil with carbon in it this time, plugs still clean... Doesn't smoke idling/revving unloaded (until you hit 10k+, then a little bit of black smoke in fits and starts) that I've seen, hence some of my confusion, but don't know while riding under load... Not enough to notice in the rear view but that isn't saying much... Haven't tried new plugs, the ones in there are from the last service a few weeks before I bought it.

No smoke on starting after leaving overnight but I'll double check that when I get home...

[jono035]

Uh huh a little bit of knowledge is dangerous there are plenty more variables to be taken into consideration.

So very true, hence why I'm trying to find out as much as I can before I attempt to use car-learned skills on a bike engine!

[T.W.R]

Well are the plugs oiling up in a uniform manner? is there variation or are all equally oiled up?
Any oil in the airbox?

Have you changed the brand of oil you're using recently? is it synthetic or mineral.

A comp/leakdown test will be an indicator of cylinder condition but you've got to take the condition of the valve seats as a variable to be considered in the readings

Whip the carbs off & the header pipes off and have a look down the inlet ports & exhaust ports, you'll see the valve stems and will notice any wetness from seepage from worn valve seals.

If you get into as you'd mentioned cracking the cases & doing crankshells etc more money involved than you'd expect & not a viable option.