Piston difference

[XSokieSPECIAL]

General information
Model: Yamaha XS 850
Year: 1980
Category: Touring
Rating: 77.4 out of 100. Show full rating and compare with other bikes
Safety: See our safety campaign with the high safety rated bikes in this category.
Engine and transmission
Displacement: 826.00 ccm (50.40 cubic inches)
Engine type: In-line three
Stroke: 4
Power: 79.00 HP (57.7 kW)) @ 8500 RPM
Compression: 9.2:1
Bore x stroke: 71.5 x 68.6 mm (2.8 x 2.7 inches)
Valves per cylinder: 2
Fuel control: DOHC
Cooling system: Air
Gearbox: 5-speed
Transmission type
final drive: Shaft drive (cardan)
Physical measures
Weight incl. oil, gas, etc: 258.0 kg (568.8 pounds)
Chassis and dimensions
Front tyre dimensions: 3.25-19
Rear tyre dimensions: 4.00-18
Front brakes: Dual disc
Rear brakes: Single disc
Speed and acceleration
Top speed: 196.0 km/h (121.8 mph)
Other specifications
Fuel capacity: 24.00 litres (6.34 gallons)


General information
Model: Yamaha XS 1100
Year: 1980
Category: Classic
Rating: 79.4 out of 100. Show full rating and compare with other bikes
Safety: See our safety campaign with the high safety rated bikes in this category.
Engine and transmission
Displacement: 1101.00 ccm (67.18 cubic inches)
Engine type: In-line four
Stroke: 4
Power: 95.00 HP (69.3 kW)) @ 8500 RPM
Compression: 9.2:1
Bore x stroke: 71.5 x 68.6 mm (2.8 x 2.7 inches)
Valves per cylinder: 2
Fuel control: DOHC
Cooling system: Air
Gearbox: 5-speed
Transmission type
final drive: Shaft drive (cardan)
Physical measures
Weight incl. oil, gas, etc: 286.0 kg (630.5 pounds)
Chassis and dimensions
Front tyre dimensions: 3.50-19
Rear tyre dimensions: 4.50-17
Front brakes: Dual disc
Rear brakes: Single disc
Speed and acceleration
Top speed: 215.0 km/h (133.6 mph)
Other specifications
Fuel capacity: 24.00 litres (6.34 gallons)

[MartyA]

Dunno if this will help, but in post #15 where the old and new pistons are on the same pin the old piston looks to be taller on the pin. Due to that height difference I'd be careful swapping pistons. Did I miss the post, did that actually come out of a 78E? The new piston does look like my old 78 pistons, with just a little relief cut on top at both ends. I don't recall ever seeing that big relief cut into the side of the piston when talking about XS11's, but I've not seen any 750 or 850 parts. Seems to me that the higher crown could increase compression, but cutting that big relief in the piston would negate that increase, not to mention mess with the vapor "swirl" intent of the head.

As posted - interesting....

[red bandit]

Two different people have a set of jugs w/ pistons on e-bay right now. All the pistons have that cut out. They say they are from a 78. Who knows??

[Flatlander]

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

???YUP???



Tarzan,
How does the head look? If the piston was beat and had possible "hot spots", I wonderin if the head may too??? Just something to look at if you allready haven't. And wondering what caused the damage and how to prevent future failure or damage to other cylinders.?

[tarzan]

I took the two pistons to work last week and measured and weighed them both.
I found both pistons to weigh within .3 of a gram of each other.IIRC the older one was 198.6 grams and the new one is 198.3 grams.That diff could be the weight of the carbon on the one.

As for measurement,they are both within .005 in height.The pin location is within .004.I even measured the where the radius of the dome starts and it is within .005.

The only concern now is how much that indent will change flow and compression.Could the volume diff mess up sync at as the engine increases rpm since the bike will be synced at idle?
I am thinking I should just install the new piston and go with it.

As for the head,yes it does have the same pitts in it as the piston.
I have a 1980 head and cams with low miles and is in good shape that I will use on this motor.

I do think I could reuse the old head and piston if I had to because that cylinder ran ok.A different cylinder is the offender and reason for the teardown.I just found the damage when I went in.

[trbig]

Throw it in and run with it. Throw a VERY LIGHT hone on the cylinders and put it back together. When you sync the carbs, you are equalizing everything there. There won't be enough difference to hurt anything even if it does flow a bit different. I've seen bikes run fine with compression from high to low being 150 and 90.

A light hone should get the rings all re-seated back in and give a bump in compression anyway. Just orient the rings correctly per the manual, and it would help to have a few buddies there if possible when fitting the cylinders back over the pistons.


Tod

[tarzan]

I already honed all the cylinders,so I am ready for reassembly.

I also have a set of 1st over rings I was planing on fitting.Although I probably could still use the old rings I suppose,they look good still.

And yea,I was wondering how to get the cylinders back on by my self.
Has anyone tried to install the pistons in the cylinders while on the bench and then, with the pistons sticking out the bottom of the cylinders,install the pins on two cylinders then turn crank and install other two pins,then push cylinders all the way down?

[trbig]

Your method is the tough way to do it. When trying to install the pins and pin clips on the end, one bad movement and the rings pop out of the cylinders.

I have done it many times alone, it just takes some patience. When you push down on one side of the cylinders to get some rings into the bore, the other side you just got in pop out. It's nice if you can have even one more person. It's a lot easier to watch just two pistons than four.

I've also used 4 big hose clamps as ring compressors. Lightly tighten them over the rings with a good soaking of oil... it will encompass all three rings. You should be able to easily spin the clamps on the pistons. You want them to be able to slide down fairly easily. Set the cylinders over the top of the pistons. Put them all at mid-stroke. Give one firm even downward push.. don't rock it at all or the rings pop back out... and after trying this several times, they will all slide up into the cylinders. The clamps will be pushed down to the rods and you can remove them there. It will probably take several tries at this, but it can be done this way.

As for your rings, don't go by looks at all. Do an end gap measurement on them. Stick the rings into the cylinder bore each one at a time. You can use a piston minus the rings to push them down into the bore about halfway squarely. Use a feeler gauge to measure the end gaps. Your stock ones may be out of spec and your 1st over may be too close. You'd have to lightly file the 1st over to fit.

Tod

[Flatlander]

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

Still a ???YUP??? on this.

[XSokieSPECIAL]

Still a ???YUP??? on this.

OK. I'll take the bait.

What is your ???? about, other than it has it has no connection with the 1100 engine.

I was just trying to give an example.

I built engines for sprint and modified stock cars several (20) years ago. I still have a lot of SB Chevy specs BRANDED into my brain.

Best example I could think of.

[trbig]

Don't ya hate stuff like that? Can't remember where you put your keys or SWMBO's birthday because all that other crap stuck in there... lol.


Tod

[MartyA]

Don't forget the assembly grease!

[mro]

took the two pistons to work last week and measured and weighed them both.

To see what differences may be you can take a beaker (large enough to hold a piston) and measure how much water it displaces. Helps if the beaker has a cc scale on it.

mro

[DiverRay]

To see what differences may be you can take a beaker (large enough to hold a piston) and measure how much water it displaces. Helps if the beaker has a cc scale on it.

The only problem with that is that IT HAS NOTHING TO DO WITH ENGINE DISPLACEMENT!! The part you need to measure for that is between the top of the piston and the head.
I HAVE pulled a clean 78 engine apart, and it did NOT have the "notches" in the valve relief area! I think you have the 850 pistons in your engine!
This is just my humble opinion, as we all know, everyone has one, and the ALL stink!

[Flatlander]

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

I thought that you had to change the crank, not the wrist pin location in the piston, to get a differant stroke length?