Misfire under load

[Jan_P]

I have had bad cam bearings on my first ca 70 000 km
Bordering to fall apart . If I Recall right the left side
Compression soft but no re bore
One crank bearing
And CAM replaced .. Pitting at some lobe edges

One can inspect them cam bearings and listen if rattling. When cleaned.
If good quality bearings available I would replace.
I also regularly replace springs. Cant tell about valve springs here.
I believe I have replaced every time in there 3 - 4 times
Probably a bit to often
Again this is not an exact science the work taking the engine out and in with gaskets and seals
I do more once in there .Pushing the next time longer into the Future
I feel like a fool, doing it over again close in time.
Sleeping better
Sure it costs a bit more in parts but ill take that .. Never had any plan selling it.

 

[this old xs]

Your expert in that link offers race engines as an example of why you should "polish" cylinders instead of honing. I don't know if any of that is true or not (I'm very skeptical), but consider... the engines he's made an example of have to last, at most, 500miles before they get tore down and rebuilt. So if polishing the bores gives 'em a few more horsepower, more power to 'em... pun intended. They're short lived race engines... a completely different world from a road engine.

That doesn't really carry over to a road engine we'd like to see many thousands of miles out of. There's two reasons we hone. To aid in seating the rings and and bore together... and for oil retention. I'd guess that if true, the race guys aren't really concerned with the latter... it's only got to last 500mi after all. That's not us, we'd like to see several zeros added to that number. I'd be willing to bet polished cylinders won't get us there.

I've replaces hundreds of cylinders on aircraft engines, as well as boats, cars and motorcycles. At every airplane shop I worked at, failing to hone the cylinders would have been grounds for termination.

Your "expert" in that link is just a faceless voice on the internet, so his advice should contains some grains of salt... just like my faceless internet voice.

I mainly chuckled at the bun fight in that honing thread. It's amazing what can turn into a contentious issue, and how bent out of shape people can get over it.

 

[Paul Sutton]

I'm an ugly bastard so best I remain faceless too...

 

[this old xs]

Been busy/procrastinating, progress is slow (having another bike to ride definitely contributes). Cylinders are back on, did the clutch pushrod bushing, new timing chain and guides etc are in place. Even got new orings for the cylinders.

I filled the combustion chambers with diesel (because that's what I had handy) and all 4 valves leaked, but only a small amount and only after days. I pulled one inlet and the faces look brand new. There was a little bit of carbon on the valve seat which came off with my fingernail.

I decided to try something a bit wacky, I lapped the valves without grinding paste. They really seem that good that I think even the fine grit is too much. No grit might be not enough, we'll see, combustion chamber is full of diesel again.

Looking at the carbon on the back of the inlet valve, and considering there's no bypass on the pistons, I'm thinking the oil had to be entering the intake via the breather? I read here that filling to the top mark is too much? I think it is oil carbon because it was hard.

 

[Its been a long time]

Been busy/procrastinating, progress is slow (having another bike to ride definitely contributes). Cylinders are back on, did the clutch pushrod bushing, new timing chain and guides etc are in place. Even got new orings for the cylinders.

I filled the combustion chambers with diesel (because that's what I had handy) and all 4 valves leaked, but only a small amount and only after days. I pulled one inlet and the faces look brand new. There was a little bit of carbon on the valve seat which came off with my fingernail.

I decided to try something a bit wacky, I lapped the valves without grinding paste. They really seem that good that I think even the fine grit is too much. No grit might be not enough, we'll see, combustion chamber is full of diesel again.

Looking at the carbon on the back of the inlet valve, and considering there's no bypass on the pistons, I'm thinking the oil had to be entering the intake via the breather? I read here that filling to the top mark is too much? I think it is oil carbon because it was hard.

Quite possible that oil is pulled down the inlet valve stem seals. The inlet valve stem seals see a pretty high negative pressure at low throttle openings. Presumably given the work you are doing the stem seals will be replaced anyway.

 

[this old xs]

Nice suggestion, thanks. Yep, all new valve stem seals.

 

[Jan_P]

Are you sure have been lapping long enough
The one I have has 2 types compound one coarse and one finer

Maybe it is the picture but as I recall it there should be more shiny surface and no dark stains

 

[Adamc]

Are you sure have been lapping long enough
The one I have has 2 types compound one coarse and one finer

Maybe it is the picture but as I recall it there should be more shiny surface and no dark stains


View attachment 340010

Looks like they need some lapping in to me.

 

[this old xs]

Yeah, that picture was before lapping I maybe should have done more (nice and shiny) but it is what it is.

Progress! Amazing what you can get done when you take a day off.

 

[this old xs]

Oof. 12 or so hours and she's back together and running (didn't put the side covers on). Sounds like a bag of hammers still Sub optimal.

Using the screwdriver to the ear trick it seems to be coming from the right hand side or maybe the middle behind the cylinders. There was forbidden glitter in the oil but I thought maybe clutch friction material. The sump plugs beg to differ though. I thought that might be the starter doing typical XS650 starter things (I squished the spring while I had the motor out), but that's a lot of material. Plus that big chunk is very suspicious.

I thought maybe rod knock but it doesn't sound right. I'm thinking failed gearbox bearing at this stage. Sigh.

It's way too late now and I was sick of working on it a couple hours ago, but I might take it for a quick spin tomorrow to at least see if the misfire is cured...

 

[Its been a long time]

Oof. 12 or so hours and she's back together and running (didn't put the side covers on). Sounds like a bag of hammers still Sub optimal.

Using the screwdriver to the ear trick it seems to be coming from the right hand side or maybe the middle behind the cylinders. There was forbidden glitter in the oil but I thought maybe clutch friction material. The sump plugs beg to differ though. I thought that might be the starter doing typical XS650 starter things (I squished the spring while I had the motor out), but that's a lot of material. Plus that big chunk is very suspicious.

I thought maybe rod knock but it doesn't sound right. I'm thinking failed gearbox bearing at this stage. Sigh.

It's way too late now and I was sick of working on it a couple hours ago, but I might take it for a quick spin tomorrow to at least see if the misfire is cured...

Sorry to hear this. I take it those metal shards are on drain plugs that were clean last time you looked? Next thing will be dropping the sump plate off to look at the strainer. Then see what you find in there and in the right side filter. Hope it turns out not as serious as you first fear.

 

[this old xs]

Yeah, and this oil has about 50 miles on it IIRC.

Thinking on it more, I'm inclined to think it's a broken or chipped gear tooth maybe. Bearing noise would be more of a rumble but this is clanging and clattering. Think I'll have to split the cases to investigate.

 

[this old xs]

Silver lining? Seems I can split the cases without taking the top end to pieces again

https://www.xs650.com/threads/gearbox-removal-and-repair.27935/

Right or wrong, that's what I'm going to try and do anyway

 

[Jim]

Silver lining? Seems I can split the cases without taking the top end to pieces again

https://www.xs650.com/threads/gearbox-removal-and-repair.27935/

Right or wrong, that's what I'm going to try and do anyway

You can. I'd suggest pulling the right cover and clutch first before pulling the engine. Have a good look in there.

 

[this old xs]

Welcome back to my bench, its ground hog day again here in the shed. Deja vu all over again.

Long story short, it wasn't like any rod knock I've heard, maybe its just what eating rollers sound like. Or maybe plain bearing crank rod knock sounds different. At least I was right about the location. Makes sense now, the gold coloured forbidden glitter suspended in the oil was probably the rod and the stuff on the drain plugs was the rollers I assume. At least a couple are AWOL.

Pretty hard to take pictures of the big ends as I'm sure you'll appreciate, but on one you can see the rollers, the other, not so much. I guess at least two are gone.

Funny enough rocking it back and forward the rod seems fine. I'm guessing it's very oval inside there somewhere though because that noise is happening.

I guess people just buy a whole crank these days? I'll check geoffsxs. Almost 25 years ago I had a RD350 crank rebuilt but I wouldn't know where to take it these days.

 

[Its been a long time]

Welcome back to my bench, its ground hog day again here in the shed. Deja vu all over again.

Long story short, it wasn't like any rod knock I've heard, maybe its just what eating rollers sound like. Or maybe plain bearing crank rod knock sounds different. At least I was right about the location. Makes sense now, the gold coloured forbidden glitter suspended in the oil was probably the rod and the stuff on the drain plugs was the rollers I assume. At least a couple are AWOL.

Pretty hard to take pictures of the big ends as I'm sure you'll appreciate, but on one you can see the rollers, the other, not so much. I guess at least two are gone.

Funny enough rocking it back and forward the rod seems fine. I'm guessing it's very oval inside there somewhere though because that noise is happening.

I guess people just buy a whole crank these days? I'll check geoffsxs. Almost 25 years ago I had a RD350 crank rebuilt but I wouldn't know where to take it these days.

Sympathy, that's not a great outcome for you. Good luck with the crank rebuild. Like you say, there's not so many shops do this work now that we don't have two stroke engines any more.

 

[Dunc]

Where in Oz are you?

 

[this old xs]

Where in Oz are you?

Northern NSW, New England region.

 

[this old xs]

Hmm. Just watched a video of a fella rebuilding his XS650 crank in his shed with a dodgy ebay hydraulic press. I own a dodgy ebay hydraulic press...

 

[Raymond]

Hmm. Just watched a video of a fella rebuilding his XS650 crank in his shed with a dodgy ebay hydraulic press. I own a dodgy ebay hydraulic press...

Allen Millyard builds cranks for exotic specials in his shed with not much more than that, but he is a sort of genius. Most of us would either track down an engineer who can do the job or buy a s/h crank? I'll be interested to see what you do and how you get on. Good luck, Raymond