pistons

[81sx1100]

Hey all I want to do a top end on my 81 xs1100 the psi's were very low and the bike has 63k on it (was an old police bike) cycleder #1 85 psi #2 80psi #3 58psi and #4 75psi the spec is 142psi so i think it is time to do a top end but i am having trouble finding new pistons for it so i can go 0.010in (1 Over) have it bored and honed new rings ect... any thoughts where i can get new pistons a 0.010? thanks

[DGXSER]

First off, not to insult your abilities or anything, but did you make sure you had the throttle open all the way when testing the compression? It makes a BIG difference.

Second, have you checked the valve clearances? They could cause bad compression numbers.

As to oversize pistons, the only new pistons I am aware of are form the big bore kits out there. They are more than .010 over, but they will increase performance as well.

[ManagerMike]

With those readings, the engine shouldn't even run
general rule of thumb for a normally aspirated gasoline engine is it takes at least 90psi of compression to ignite the air fuel mixture.(There are exceptions of course)
I'd re-run that test.

[tinman905]

It's usually much easier and cheaper just to buy a big bore kit. But you can find a half decent used engine out there cheaper than a big bore kit. Used engines can be found from $99.00 up to $300.00 that are in good shape. Take some time make sure it's your rings and pistons that need replacing.

[DiverRay]

I agree with doing a re-test.
#1 Adjust valves to specification. The valve lash will CLOSE on the XS1100, NOT open up. If they have not been checked for over 10K miles, you are overdue and may be getting close to burning a valve.
#2 Re-run compression test with throttle held wide open.
#3 Most of the bikes here have well over 80K miles and still run well. Rings on this bike should go for 110 to 150K miles with no problems.

[natemoen]

If its been sitting for awhile the rings could just be stuck and not really doing their job and may loosen up after some miles are put on her.

[81sx1100]

Thanks all for the information i will re-do the comprestion test with the throdle wide open i did not know and DGXSER you didn insalt me one bit i can work on cars like theres no tomorrow as for bike new to it but anyway i will redo the test and check the valves to make sure they are near or clost to specs thanks all again keep ya up to date and still no blinking for turn signals yet either lol

[81sx1100]

With those readings, the engine shouldn't even run
general rule of thumb for a normally aspirated gasoline engine is it takes at least 90psi of compression to ignite the air fuel mixture.(There are exceptions of course)
I'd re-run that test.

the bike does run ruff but runs lol

[Haarstad]

#2 Re-run compression test with throttle held wide open.

I did not know that, i'm gonna re-check mine now...

[tarzan]

If it does end up needing rings, the cylinders are probably still within spec.
The cylinders are pretty hard on these.The wear most likely is in the rings.
I would check the bore to be sure, but then would go with first oversize rings.
I used 1st oversized and honed the cylinders and filed the rings for proper end gap.
The bike came back up to 150 to 160 compression on all cylinders.

[81sx1100]

If it does end up needing rings, the cylinders are probably still within spec.
The cylinders are pretty hard on these.The wear most likely is in the rings.
I would check the bore to be sure, but then would go with first oversize rings.
I used 1st oversized and honed the cylinders and filed the rings for proper end gap.
The bike came back up to 150 to 160 compression on all cylinders.

I will keep that in mind but going to re-test each cyclender the right way first lol

[cowboybob998]

pistons

APE raceing in calf. has big bore pistons for 564 dollars, send them you cylindes and they will bore them to the pistons for an extra 120.
And they allso have the oval pod air filters for 59

[81sx1100]

APE raceing in calf. has big bore pistons for 564 dollars, send them you cylindes and they will bore them to the pistons for an extra 120.
And they allso have the oval pod air filters for 59

Cowboybob998 that would be nice and all but i am not going to send my pistons all the way to CA but thanks for the tip and help

[Rickrod3]

How does the engine run?

If it does end up needing rings, the cylinders are probably still within spec.
The cylinders are pretty hard on these.The wear most likely is in the rings.
I would check the bore to be sure, but then would go with first oversize rings.
I used 1st oversized and honed the cylinders and filed the rings for proper end gap.
The bike came back up to 150 to 160 compression on all cylinders.

How many miles does the engine have on it and does it use much oil?
working on an engine and considering going this route.

[crazy steve]

How many miles does the engine have on it and does it use much oil?
working on an engine and considering going this route.

Even the 1st oversize rings are hard to find (and about $50 per piston when you can), so don't count on doing this; Tarzan lucked out and found a set. The 'big bore' kits are the only readily-available piston/ring sets still out there, and at $600 for the kit and another $100+ for the boring, not the cheapest fix either. That's why good used cylinder/piston sets are still worth money...