Low Compression?

ThatFiveOhTho wrote: You mentioned release. The pressure release for draining pressure when the gauge is done being used is ok at the gauge base, it's the Schrader valve you don't want at the base of the gauge.

If you don't have any residue or performance impairment and you like the way the bike rides, ride it.

The question comes whether a rebuild or teardown is worth fixing having to fill up or top off. As more issues arise throughout owning the bike, that question becomes easier to answer with more time, eventually becoming absolute on a long enough time line as things break and wear normally.

Great points...each and every.
Would have thought the bottom end woulda mentioned something by now, but it just keeps on crank'n.

SWest wrote: Looks good.
Steve

Had to try it...
Pulled out the cork, and stuffed the Comp baffle in the meg for an evening test-ride.

:ohmy:

No comparison...like a totally different bike! She's, she's...I can't find the words to describe it. I thought she was fast and powerful enough already, but something happened that I just can't understand. :whistle:

Forget what I was whining about, because it doesn't matter now.


:woohoo:

I'd like to hear it.
Steve

SWest wrote: I'd like to hear it.
Steve

I'd love to shoot a video with my camera, but I have no idea how to post it. I think my son may be able to help me do that.
Any suggestion toward that would be greatly appreciated.

Use movie maker. If the file is small enough you can post it direct to your thread like pics.
Steve

Glad you tried the comp baffle..... I remember almost begging you to try it on one of those dyno runs as I love mine and I'm leaving mine in too.

You said your bike specs at 8.9 to 1 fresh too so that's a little lower than most that come with 9.5 and 10 to 1. I was getting your numbers maybe 5 or 10 more before the build (the one that was always low by 10 lbs from when I bought it with 1,700 miles had a bad spot 1 inch grooved up but smoothed over just behind the pin on #3) ...... Wanted to build oil pressure so I checked my new pistons while doing that and I got 160 even across all 4 before I even started it for the first time and 165 after 600 miles with the new 700s.... need to check it again sometime 1,400 now.

I use a hold in rubber tipped type that I got at Farm and Fleet for only 13 bucks 3 or 4 years ago..... for that $ maybe you could get it and compare ? Never thought of that before ... with the plugs filling that hole it will be slightly higher ...cool.

Scirocco wrote: Thats why you have to crank more than 10 times to get the highest value as a real value.
And all spark plugs out to get full revs as you can.

If the check valve is in the wrong place, it wont matter how many times you crank it. The pressure in the hose wont build up to the maximum because it deflates every time the exhaust valve opens. Because the hose has a little resistance in it, it will hold a tiny bit of pressure, but will never hold full compression.

Whoever designed the gauges with the check valve at the gauge end of the hose did not understand the whole point of the tool. And because they were cheap, there are a lot of them out there.

And yes, all plugs should be out. It's also important to disconnect the coil primary wires to prevent damage to the ignition. Or you can put the plugs in the wires and let the plugs rest on the engine.

Daftrusty wrote: If you used a compression tester with a really long hose and the check valve is at the gauge, then the numbers come out much lower than they really are. What happens is that the volume of the hose becomes part of the combustion chamber and it lowers the amount of air pressure being compressed into a now larger space.
If your tester has the check valve right at the threaded end that goes in the head, then you should be worried. But your numbers are close together so I have a feeling it is just the gauge (the hose) that is skewing your results.

Yes, there is a schrader valve at the threaded end of the hose, and a pressure-release button to press after the reading is taken located directly below the gauge. The rubber hose is about 16" long and has a quick connect fitting to attach the gauge unit.



Many hours later:

So...did I ride the piss out of it, or what?


:woohoo:

Sure don't feel like it!

Does this engine have long duration cams installed? If so that will reduce cranking compression.

Nessism wrote: Does this engine have long duration cams installed? If so that will reduce cranking compression.

Hmm...

kzrider.com/forum/2-engine/592527-gpz-cam-swap#620000

...includes the following:



1982 KZ1100-A2, rated as 92 hp:

Intake (12044-1027):

Duration: 270 - Lift: Not exactly sure, but a little less than the 81 GPz.

Exhaust (12044-1027):

Duration: 270 - Lift: Not exactly sure, but a little less than the 81 GPz.

Used on:

KZ1000-K1 (LTD) (1981)
KZ1000-K2 (LTD) (1982)
KZ1000-M1 (CSR) (1981)
KZ1000-M2 (CSR) (1982)
KZ1000-P1 to P24 (Police 1000) (1982 - 2005)
KZ1100-A1 (Shaft) (1981)
KZ1100-A2 (Shaft) (1982)
KZ1100-A3 (Shaft) (1983)
KZ1100-D1 (Spectre) (1982)
KZ1100-D2 (Spectre) (1983)
KZ1100-L1 (LTD Shaft) (1983)
ZN1100-B1 (LTD Shaft) (1984)
ZN1100-B2 (LTD Shaft) (1985)



1981 KZ1100-B1 Gpz, rated as 102 hp:

Intake (12044-1031):

Duration: 280 - Lift: 8,4 mm (.330") - Open: 35 BTDC - Close: 65 ABDC

Exhaust (12044-1036):

Duration: 280 - Lift 8,8 mm (.346") - Open: 68 BBDC - Close: 32 ATDC

Used on:

KZ1000-J1 (1981)
KZ1000-J2 (1982)
KZ1000-J3 (1983)
KZ1000-R1 (Eddie Lawson Replica) (1982)
KZ1100-B1 (GPz) (1981)



1982 KZ1100-B2 GPz, rated as 109 hp:

Intake (12044-1037):

Duration: 288 - Lift: 8,8 mm (.346") - Open: 34 BTDC - Close 74 ABDC

Exhaust (12044-1037):

Duration: 288 - Lift: 8,8 mm (.346") - Open 72 BBDC - Close 36 ATDC

Used on:

KZ1000-R2 (Eddie Lawson Replica) (1983)
KZ1100-B2 (GPz) (1982)



1983/84 ZX1100-A1/A2 GPz, rated as 120 hp:

Intake (12044-1057):

Duration: 300 - Lift: 9,6 mm (.375")

Exhaust (12044-1057):

Duration: 300 - Lift: 9,6 mm (.375")

Used on:

ZX1100-A1 (GPz) (1983)
ZX1100-A2 (GPz) (1984)

So if the current train of thought is accurate, then simply installing a set of shorter duration original KZ J-model camshafts should increase the compression to a level more-acceptable?

I, personally am not trying to come to a conclusion about your bike specifically, and the 550's are obviously different from your bike, but in my experience I find the standard 550's have about the same compression result as the gpz 550's. That is, the standards have a 9.5:1 comp ratio, whereas the gpz's have a 10.0:1 ratio. But the gpz's have higher lift, and more importantly, longer duration cams. In the end, the compression test pressure ends up about the same. I usually see them in the 170 psi to 190 psi range, with most being in the 180's. (Using many different gauges on many different engines over many years. Two of my gauges differ from each other by about 10psi when measuring in the 180 psi range, so there is also the question of gauge condition etc.)

So, as Ed said, longer duration will lower static compression test results. Can't say by how much as I've never tried a gpz cam in a standard motor.

Does the FSM give you a number for what the comp test should be minimally?