Piston difference

[Guy_b_g]

It could be to unshroud the intake valve right at opening, but it's not for clearance.

I agree, it's got to be someone's idea of a performance upgrade. Not a very effective one either with the compression loss from removed material, I bet.

Do the other 3 look like that?

[tarzan]

Hey Guy,
I was out working on my XS850 and was flipping through the book and there is a picture of a piston from an XS750 that has that same indent.So I wonder if the XS850 has them too as the 850 and 1100 have the same bore.

[XSokieSPECIAL]

So,

Is the difference in stroke length compensated for in connecting rod length.

If this is indeed an 850 piston the pin position is the same, as illustrated in the pic.

I wonder if there is some benefit in running the 850 piston in the 1100, or., the P.O. just needed a piston and this is all he could get his hands on.

Things that make you go HHMMMMM.


Greg

[Guy_b_g]

I really don"t know.

I looked thru the parts lists at BikeBandit, and they don't list the 850 until 1980, but the piston for the 1100 of that year is a different part number than the 850.

The piston for the 1100 of '78 is different than the '80 850 or the '80 1100, but as to the strange valve relief, I can't say...but I do know I haven't seen anything like that on an 1100 of any year.

But I am far from being an expert..so maybe someone who has seen a lot of these pistons from various years can come to the rescue?

Maybe Andreas?...he's torn down a lot of these engines, I bet.

[Guy_b_g]

Is the difference in stroke length compensated for in connecting rod length.

The 850 may have had a different stroke length, but the main difference in capacity was the fact that the 850 had 3 cylinders.

[XSokieSPECIAL]

Yea, But I am speaking of capicity per CYLINDER.

Chevrolet 350ci and the 327ci have exactly the same bore but different stroke. The 350 and the later large journal 327 share the same block and the same connecting rods. The difference is in the wrist pin height in the piston.

I.E. the distance between the top of the wrist pin and the top of the piston.

350 had a stroke of 3.48" and 327 had a stroke of 3.25".

Confused yet?

Greg

[tarzan]

I really think this bike came with the pistons with an indent.They are all four the same and the bike has 44,000 miles on it and it looks like that is about right.
In seeing the pic of the smaller bikes piston with the same indents just makes me think that it isn't out of the ordinary.I also saw pics of pistons without that indent in the triples manual. It would be nice if they made them all the same.Oh well .
Thanks for all the input.
Rick

[XSokieSPECIAL]

I really think this bike came with the pistons with an indent.They are all four the same and the bike has 44,000 miles on it and it looks like that is about right.
In seeing the pic of the smaller bikes piston with the same indents just makes me think that it isn't out of the ordinary.I also saw pics of pistons without that indent in the triples manual. It would be nice if they made them all the same.Oh well .
Thanks for all the input.
Rick

I wonder if they were all produced at the same facility. Or was there more than just one?

Ahhh--- this is just strange that no one has ever seen this before.

I'm an engine person. This kinda bugs me. I need to know more.

I'm gonna see what I can find out, if anything.

Greg

[Guy_b_g]

I don't know Greg, the 850 may have had the same stroke as the 1100, or it may have been different. It must have been very close though or the side loads on the pistons would be very different with the pins in the same place on both engines and different stroke lengths.

[XSokieSPECIAL]

Probably just thinking TOO much.

However, if you divide 850 by 3 it comes up 283.3, if you divide 1100 by 4 it comes up 275. not real accurate but interesting that they're so close, about 8 cc per cylinder, too each other.

Doesn't really matter I guess. My train of thought just took a side track.

Anyway I'll just shut up about that. And NO I'M NOT REALLY CRAZY----NO I'M NOT.

Just don't try and take any of my crayons!

Greg

[tarzan]

if you divide 850 by 3 it comes up 283.3, if you divide 1100 by 4 it comes up 275.

Actually an XS850 has 826cc's.So 826/3=275.333.hhmmmmm......

So it appears that the two probably share the same stroke.
I looked in the triples book to see what the stroke is but it only showed bore.
But I also saw a NOS connecting rod for sale on ebay that claims it will fit the XS750,XS850,and the XS1100.

[XSokieSPECIAL]

The 1100 is actually 1102 divided by 4 = 275.5.

Don't ya just love stuff that makes you go HMMMMMMMMMMMM?

[XSokieSPECIAL]

Man, I just looked up the specs. on both engines.

The bore and stroke in 1980 are exactly the same on both engines. Even the compression ratio.

I wonder why the different part #s. Maybe that crazy valve relief?

[skids]

One has to wonder about your other 3 pistons...

[XSokieSPECIAL]

One has to wonder about your other 3 pistons...

Hhmmmmmmmmm = wonderment.