Misfire under load

[this old xs]

Well guys, it's been decided for me. Coffee cruise today and a noise gradually started. It got more pronounced to where I definitely wasn't imaging it, then it slowly turned into a most horrific clattering and hammering. I was wincing all the way home limping along at 3,000 RPM.

It's coming from the top end and the bike runs absolutely fine. I suspect the front cam chain guide has failed? I was going to replace both guides when doing the cam chain anyway based on what I've read here about them separating.

Only changed the oil yesterday too! I will update this thread with what has happened and if the cam chain replacement cures the misfire (I'm 99% certain it will).

 

[this old xs]

Way past my bedtime and I've got work in the morning. Will deal with the rest later.

 

[this old xs]

Well there's your problem. I wasn't sure what these actually look like so until I pulled it out I wasn't sure. Didn't chew into the aluminium much.

Should I replace the rear one too?

 

[Its been a long time]

View attachment 339204

Well there's your problem. I wasn't sure what these actually look like so until I pulled it out I wasn't sure. Didn't chew into the aluminium much.

Should I replace the rear one too?

Well done pulling that out before the engine got full of aluminium shavings. Myself, with the engine apart I would replace the rear one if it's original. Irrespective of condition, it's still clocking on for 50 years old.

 

[this old xs]

Can anyone advise on this please?

https://www.heidentuning.com/xs650-.../cam-chain-tensioner-complete-set-detail.html

I've reviewed 5twins' post on tensioner differences (he's the tensioner guru, not gggGary, apologies)

https://www.xs650.com/threads/cam-chain-tensioners.1056/page-2#post-465622

And I've definitely got the type D. Seems like the simplest way to change mine over would be to buy the Heiden tuning one which looks like a type E??? I'm open to suggestions.

 

[Its been a long time]

Can anyone advise on this please?

https://www.heidentuning.com/xs650-.../cam-chain-tensioner-complete-set-detail.html

I've reviewed 5twins' post on tensioner differences (he's the tensioner guru, not gggGary, apologies)

https://www.xs650.com/threads/cam-chain-tensioners.1056/page-2#post-465622

And I've definitely got the type D. Seems like the simplest way to change mine over would be to buy the Heiden tuning one which looks like a type E??? I'm open to suggestions.

Next year, I will probably upgrade my 77 650D to the type E tensioner along with the single outlet breather. Both available from Heiden. It's EUR 20 shipping from Netherlands to the UK so I have to order enough to makes it worthwhile the shipping cost anyway.

I suspect wherever you buy these from they're going to originate from the same factory so I will shop around for the best combination of price and shipping cost.

 

[Adamc]

Sorry I’m late to this thread; but looking forward to the progress on the project.
Any input I offer should be taken with a pinch of salt.

 

[this old xs]

I've ordered the OEM chain from Yamaha (bonus: cheaper than aftermarket) but the front guide is NLA so I'll get that from Geoff's XS. The cam bearings are mint, but for the sake of another $100 I think I'll suck it up and replace them while I'm in here. Though that $100 pains me, it'll pain me more to have to do it all over again!

Going to make lemonade from the lemons. Been needing to replace the clutch pushrod bushing and do the starter motor spring fix (which I should have done when changing the oil on Saturday). Very tempting to lap the valves and put new valve stem seals on but you have to stop somewhere.

 

[Jim]

Very tempting to lap the valves and put new valve stem seals on but you have to stop somewhere.

That's not the place to stop. As you said above, these rubber bits are pushing 50+ yrs. I'll promise you those stem seals are hard as rocks.... they need replacing.

 

[this old xs]

And I couldn't resist. Head will come off, valves getting lapped and new stem seals. Hopefully there's no unpleasantness lurking in the cylinders.

 

[Jim]

The cam bearings are mint, but for the sake of another $100 I think I'll suck it up and replace them while I'm in here. Though that $100 pains me, it'll pain me more to have to do it all over again!

Fwiw, in the last 2 odd yrs I've done the top end on 5 or 6 of these motors. Haven't found a bad cam bearing yet... and haven't replaced any. If they feel good to you, save your $100 for something else is my opinion.

 

[GLJ]

If the cam bearings look and feel good I would reuse them. I've reused them 5 times on 5 different 650 engines with no problems. They have a very low failure rate.
I would take the head to a machine shop and have the valves ground, a 3 angle cut done to the seats and the guides knurled and sized if needed. Plus take the pistons and cylinder to have it checked for wear.
While you have it apart you may as well do it right.

 

[this old xs]

Dang it, already ordered them. Ah well, worse things happen.

 

[Melnic]

View attachment 339204

Well there's your problem. I wasn't sure what these actually look like so until I pulled it out I wasn't sure. Didn't chew into the aluminium much.

Should I replace the rear one too?

Been there done that. I also was lucky. I was opening it up to replace the stretched cam chain and then found mine fully delaminated and sitting right there at the bottom. There was tell tale signs of tiny plastic bits in the oil filter that should have told me I was going to see this when I opened it up.

 

[this old xs]

I've been looking at these piston crowns through the spark plug holes since I got the bike. I wasn't liking what I was seeing so it's great to finally get at them. I thought they were pitted but it was just a build up of crud.

It was hard and slightly orange so I guess tetraethyl lead from back when we had leaded fuel.

Bores look a bit glazed but otherwise good. No lip I could feel at the top. Tempted to hone and rering but I'll resist. Probably? Track record this far not great... Will bust out the telescoping bore gauges and measure the bores at some point.

1st oversize it turns out.

I wasn't going to replace the rear cam chain tensioner arm, but now I've got a good look at it... Could have bundled it with today's order

 

[this old xs]

Well boys, everything measured out mint. Both pistons are scuffed but pretty well bang on spec. Bores are plus or minus a tenth of a mm or two*. Ring end gap (ok, I only did one) is 2 thousands of an inch which is perfect.

With the cylinders off I can see better and you can faintly see the cross hatch, but it's pretty darn smooth IMO. Internet says chrome moly rings don't need a honed bore. I'll mull it over a bit longer before I do anything. Going to be hard to resist lightly honing or something.

Since I've got the cylinders off I'll definitely replace the cam chain tensioner arm. Clean up the pistons a bit, valve job and throw it all back together I reckon.

*Measured before removing, with pistons at BDC. Should remeasure.

 

[jpdevol]

https://www.amazon.com/83mm-Flex-Ho...mcx_mh_pe_im_d1_hxwPPE_sspa_dk_det_cau_p_10_1

 

[this old xs]

Thinking on this some more, and considering the pistons have no, like zero, signs of blow by, I ain't messing with it. Might rub down the skirts a little bit maybe. That scuffing might mean they need to hold a bit more oil.

This is my favourite thread on it so far though:

https://www.yellowbullet.com/threads/cylinder-wall-finish-for-moly-rings.461535/

 

[Paul Sutton]

If you are going to put back together without hone or ring replacement then avoid moving the rings about. The position they come out in is the position they should go back in. This is where they settled to on running in.

 

[Jim]

Well boys, everything measured out mint. Both pistons are scuffed but pretty well bang on spec. Bores are plus or minus a tenth of a mm or two*. Ring end gap (ok, I only did one) is 2 thousands of an inch which is perfect.

With the cylinders off I can see better and you can faintly see the cross hatch, but it's pretty darn smooth IMO. Internet says chrome moly rings don't need a honed bore. I'll mull it over a bit longer before I do anything. Going to be hard to resist lightly honing or something.

Since I've got the cylinders off I'll definitely replace the cam chain tensioner arm. Clean up the pistons a bit, valve job and throw it all back together I reckon.

*Measured before removing, with pistons at BDC. Should remeasure.

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.