Engine maintenance

[burton1234]

Hi all, Happy Holidays.

Earlier this year it generated a light metal tapping sound that went away when the bike warmed up. I initially put this down to worn piston rings or something similar but not really knowing that much about engines I haven't used the bike since to be safe. With plenty of time on my hands (thanks COVID) I stripped it down. I have stripped the engine down and this being the first engine stripdown I wanted to get some advice on if it's just the rings that would need replacing not. I have attached some pictures of the parts and there condition below. I don't have my Haynes Guide with me but all the rings measure around 0.4-0.5 gap so I am not sure what the gaps should be. I am contemplating doing the 750 upgrades so this might be a good time if more than the rights need replacing.

There is a bit of side to side movement on the conron when I hold the piston end and move it slightly left and right. Is that normal?

Any advice would be appreciated.

 

[Jan_P]

Hi
If you google you can find a service manual for the conrod play
And someone perhaps is kind enough to provide a link
if you give the model and year
I would inspect the piston pins for wear or discoloring
I would put the pin in the small end hole without the piston trying to evaluate the
play
Please inspect the piston skirts for marks
It is difficult to know what makes a sound I once had a crank bearing ..that made noises at certain positions
And then silent again
If the carburetor mixture is wrong that can also make sounds that can sound bad.
Chasing the source can involve lot of work with little result ..
Did it smoke
Does the cam and top end look OK
Camshaft bearings ?? I have had worn making noise.
Cam chain adjuster ??

 

[xjwmx]

The factory manual gives a limit of 1mm so they're good. If you were burning a lot of oil, you might want to replace them anyway to try and get more spring pressure against the walls to stop that. I've used Haynes manuals for cars, but for the XS you can download the factory manual pdf and supplements for your year. Click on the "Tech" section in the top bar. Also, mildly weird noises are kind of par for the course with this bike. Next time, post a video of the sound

 

[Raymond]

Hi Burton, tell us a bit more about the bike, and yourself. This is your first engine strip down - do you have other mechanical experience?

You have certainly jumped in. That's fine, and whether you know what you are doing - or even if you don't but are organised and willing to have a go - you will find a lot of help from the very knowledgeable people on this forum.

Now you've come this far, you should assess the pistons and see if they need replacement. The tech section has guidance on checking the pistons but - and this is where it would help to know how much experience you have - essentially you need to measure the diameter of the piston skirt and the internal diameter of the bores. If the pistons are ok and within spec, you might be able to rebuild the engine with just a few new seals and gaskets. Or you might consider having the bores honed and rebuilding with new rings. But if the pistons are too far worn, you could think about pricing up doing a 750 conversion.

Some side to side play on the conrods is normal. But if the amount of play is abnormal, this is a problem and might mean replacing the big end bearings. Which means rebuilding the crank assembly.

 

[650trader]

If we ever get up and running the Big fin 750cc Kit will be introduced at $350.00
Yamahaxs650.com Joe 650 Trader

 

[5twins]

Carefully inspect the condition of your front cam chain guide. They're a common failure on these motors now due to their age. My motor was doing the same as yours, making a ticking noise for 20 or 30 seconds after starting, and this is what I found .....

Your cylinders and pistons look to be in pretty good shape with not too much wear on them (scoring and/or scrape marks), but as mentioned, measuring is the only true test. The rings appear to have been sealing well because there's very little, if any, discoloring below them on the sides of the pistons. Leaking rings would allow hot combustion gases to seep by and that would burn the oil on the sides of the piston, staining it brown. The "new" ring end gap spec is .2 -.4mm so while yours are around the upper part of it, they're still well below the max (1.0mm). Since they seem to have been still sealing well, I'd re-use them.

The carbon build-up in the combustion chamber and on the piston tops looks normal and not excessive. You can clean it all off using paint stripper. Your valve seats do look pretty carboned over though. They're usually shiny silver rings and yours are all black. After cleaning, I would give them a light hand lapping to really clean them up.

 

[burton1234]

Thanks for all the advice.

It's a 1968 bike imported to the UK from the US. It's a 447 engine. I bought it from an older chap who was going to restore it back to new but due to health reason decided to sell the bike. It was a non-runner when I bought it but that was mainly due to non of the wiring being connected correctly so it didn't take long to get it up and running. I have done quite a bit of cosmetic work to the bike to get it 80% how I want it and plan to keep doing bits and bobs to finish it off over the next few years. I guess I should really just post a pic of the bike - see below...

I would like to think I'm pretty mechanical. I did a couple of years engineering at collage years ago, raced mountain bike for years, did a few piston changes and lots of maintenance on a 2 stroke motocross bike.

When I took the bike apart, the plastic part of the front cam chain guild had come apart from ali part so that could well the be the culprit of the noise. The description that @5twins gave sounds exactly the same.

The piston skirts have some scoring that you can see from the photo in my 1st post. Is this something to be concerned about as it sounds like the piston and cylinders might have some life left in them. Reading on the Tech section, I need to get myself a T Guage and check the measurements of my cylinders.

The cam and top end look in good condition as well as the postion pins. Both pins have two black lines on them but otherwise look great. It's very hard to feel but one of them might have a ridge on it on be slightly move warn than the other in the center. What check would people recomend I do to check if these parts are still useable?

 

[Rasputin]

Use a micrometer on the gudgeon pins. The black lines are the unworn parts, if you can feel it as you slide it through your fingers they are worn. But to what extent.
I had a clicking noise on my engine, turned out to be the big ends.

 

[burton1234]

Here is a clip of the noise I got from a friends video just after starting. My friend was filming something else and wasn't standing that close to the bike. Apologies for the background noise. https://soundcloud.com/olie-burton/xs650-noise

Measuring with a vernier and they both measure 19.96mm in every point so I am presuming they are fine but I will have a look in the Tech section as I presume the tolerances are spec'd there.

 

[5twins]

Slide them into the rods and check to see if they're a nice, slip fit or if they wobble in there. That's all I ever did to check them but thankfully, I never found any bad ones. I suppose if I did I'd pull out the measuring tools and have at them.

 

[Jim]