Wrist pin play - video

[Jon M]

As I've been going on about in another thread I'm trying to find the source of a strange engine rattle (there are lots of those threads on here! ha ha). I've pulled the jugs and the pistons look fine. They say '25' on the top which I think means first oversize so the PO must have replaced them when he did a rebuild about 15,000 km ago.

The wrist pin pushed out very easily. I oiled it and slid it into the con-rod to see if there was any play. There is, but I'm not sure I'm checking it right. I put it into the small end and pushed it up on one and and down on the other. Then wiggled it like that. There is clearly some play but is this the right way to determine this?

What do you think?

 

[Jon M]

Actually the big end has some 'twisting' play too (sorry, don't know the correct term - not side to side along the crank but tilting it left and right).

Another youtube link because I can't figure out how to embed it :-/

What do you make of this:

Update:
I measured the play and checked against the manual (via 650Skull below).
The axial play, as this is called, is well within tolerance. Max is 2mm. New is 0.8-1.0mm. Mine is at 1mm. Move along. Nothing to see here.

 

[Jon M]

And a couple of photos of the small end itself. Looks pretty good to me. There is some wear but nothing abnormal looking (to my untrained eye at least):

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[650Skull]

This is in the Manual. Measure and post back what you have

 

[Jon M]

You're quite right 650Skull. I missed that in the manual. Anyway, the crank bearings are within tolerances. I was asking about 'axial' play and there is 1mm which is near the low/new end in fact! Phew.

For the small end the manual just says to check the gudgeon pin for for excessive wear.

The pin looks fine, good in fact, so I wondered whether perhaps the small end was worn.

To be honest I think it looks fine but I'm being extra diligent and seeking a second opinion just because I've taken the engine apart hunting for the cause of a rattle and so far everything looks practically brand new in here! I'm pretty much resigned to reassembling it (with new gaskets) and just trying to ignore the weird rattle... until it gets worse.

 

[gggGary]

Yes there are endless threads about engine "rattle" but the first chore is defining and locating the rattle. A bit of slightly intermittent rattle on start up is often just "correct" cam chain tension. Soon as the chain is well oiled and perhaps warmed a bit it goes away.
Valve and valve adjuster ends that have some wear, hammering marks are near impossible to set to correct tolerance and result in a slightly noisy valve train this can probably be safely ignored. Then there are the various starter, gear train noises. Big parallel twins do shake a bit and many parts with some tolerance can be excited to rattle at certain RPMs. Deep "death" knock is another issue and that is bad news. Crank pins that have started to walk tend to cause "whirring" noise of various severity. This will need correcting but several other areas that are not assembled correctly can cause whirring also. No expert but your rod ends look like they have been running a bit hot and dry... Is the engine in a stock frame or is it in a modified bike? Builders often do not think through the issues of oil level in an engine that is tilted well fore or aft.... The small end depends on splash lube and some extra oil from tiny oil jets drilled through the crankcase from the oil gallery that runs from the pump across the front of the engine.

 

[CDNTX650]

Yeah that's a bit more axial than new that's for sure. Mine had more than that and I definetly didn't run the rods. Yours don't look to burnt or discolored. Your call I guess.

 

[TwoManyXS1Bs]

May get some ideas from these:

http://www.xs650.com/forum/showthread.php?t=29082
http://www.xs650.com/forum/showthread.php?t=28536
http://www.xs650.com/forum/showpost.php?p=384615&postcount=645

 

[Jon M]

Thanks for the input.

I've checked the tolerances and found that the pin itself is ok. But the small end seems to be too worn, explaining the excessive axial play. I have a spare parts engine and a comparison between the two small ends and pins supports this hypothesis.

So I think this probably explains the noise I can hear from the engine. So looks like I have a bigger job on my hands than I anticipated. Oh well. Thanks for listening to me while I worked through it to this point.

Now, if I'm having to get the crank separated anyway maybe this is a good opportunity to consider rephasing...

 

[TwoManyXS1Bs]

Finally was able to look at your youtube video. Yep, the connecting rod small end is worn too big. Typical rattle sounds from loose/worn wrist (gudgeon) pins occur under different rpms and loads. Usual test is to listen for a change in rattling during acceleration and deceleration. Do you recall that kind of scenario?

 

[Jon M]

Finally was able to look at your youtube video. Yep, the connecting rod small end is worn too big. Typical rattle sounds from loose/worn wrist (gudgeon) pins occur under different rpms and loads. Usual test is to listen for a change in rattling during acceleration and deceleration. Do you recall that kind of scenario?

Yes, that is exactly how it sounded. I described it elsewhere as 'irregular' and unlike valve rattle, because I couldn't quite figure out the relationship between rpm and rattle. But now I've compared the wrist pin in another con rod I can see how it is supposed to fit. I also measured the ID of the small-end with my crappy calipers and even though they are not that well suited to the task it is pretty clear that it is outside of tolerance.

The pistons look totally fine though so I'm glad I played safe and tore the engine down to investigate before the rattle got bad. It has good compression, newer pistons, newer cam chain and guides, all the valves and adjusters are good with no damage or pitting, it runs really well so it's worth spending the time and money fixing it up. Seriously considering rephasing while I'm at it!

Thanks for the input.

 

[jay760]

Looks like bare metal on the top in the first picture, should be copper coated all around, if it's worn off in one place would say the rest is pretty thin.