Wiseco big bore compression numbers?

[80GS1000]

The GS1000 has done about 800 miles since a top-end rebuild with new valves and a 1100 cc Wiseco kit. Compression numbers on all 4 cylinders are at about 120 PSI. Is this normal, or should it be higher? And if compression should be higher, is it likely to improve at this point? I've been riding the snot out of it since the rebuild out in the desert to break in the rings, WOT to redline once warm then engine braking to 2K RPM then WOT again. Cylinder #4 shows what appears to be a bit of oil fouling on the plug.

 

[Guest]

sorry to say but i think the compression numbers should be higher after a re-bore and new pistons/rings and new valves, and after that break-in mileage

would be interested in hearing from someone WHY your numbers are not better

 

[rphillips]

I can see your concern, but I've always heard the across the board readings are most important. Not how high the #'s are, but how equal the #1 thru #4 readings are.

 

[trippivot]

what thickness of base gasket and thickness of head gasket did you use? (deck height)

do you have stock camshafts at stock cam timing? (cranking pressure)

the specifics of those 3 details will have the cylinder psi adjustable up or down.

but like rphillips said equal readings are more important.

I won't even ask what piston to cylinder clearance or top ring end gap settings.

 

[80GS1000]

what thickness of base gasket and thickness of head gasket did you use? (deck height)

do you have stock camshafts at stock cam timing? (cranking pressure)

the specifics of those 3 details will have the cylinder psi adjustable up or down.

but like rphillips said equal readings are more important.

I won't even ask what piston to cylinder clearance or top ring end gap settings.

Thanks for the help.

Stock Wiseco head gasket, stock Suzuki base gasket.

.395 lift Web cams timed in by the book: http://www.webcamshafts.com/pages/motorcycle/suzuki/install_data/tc_664.html

 

[Dan Ruddock]

Try a different gage. Dan

 

[Nessism]

Obvious question but are you holding the throttle wide open when checking compression?

 

[80GS1000]

Obvious question but are you holding the throttle wide open when checking compression?

Yes, WOT with a full battery. Should the other spark plugs be removed when testing each cylinder? The 120 PSI number is with the other plugs still installed.

 

[Jim Hansen]

Compression Readings

Compression Readings

"The GS1000 has done about 800 miles since a top-end rebuild with new valves and a 1100 cc Wiseco kit. Compression numbers on all 4 cylinders are at about 120 PSI. Is this normal, or should it be higher? And if compression should be higher, is it likely to improve at this point? I've been riding the snot out of it since the rebuild out in the desert to break in the rings, WOT to redline once warm then engine braking to 2K RPM then WOT again. Cylinder #4 shows what appears to be a bit of oil fouling on the plug".


If all of the cylinder compression readings are the same, then everything is probably ok. If a cylinder had a problem with a valve or compression rings, then one cylinder would have a low reading.

If a cylinder has the same compression reading as the other cylinders, but is pumping oil, then there might be a problem with the oil ring or with the valve guides. But this is unlikely in a rebuilt engine. The engine might just need more time to break in the oil rings.

When the engine displacement is increased, this has the effect of increasing cranking pressure (compression ratio) unless metal is removed from the combustion area or thicker head or base gaskets are used. However, with a high-performance cam profile with increased valve overlap, this has the effect of reducing measured compression readings. I wouldn't worry about any of this unless you have pinging, which would be from too much compression, not from for too little.

With constant-velocity (CV) carburetors, you must not only open the throttle butterflies, but also block open the carb. slides during a compression test. Otherwise, you will get erroneous low readings. All sparkplugs should be removed during the test in order to maximize cranking speed and maximize the compression readings.

There are a lot of variables involved when making a compression test, so the results require interpretation. If you are still concerned about the results, you can always do a Leakdown Test. It's not difficult, and the leaddown testers are not expensive (But you need a compressor or some source of air). I think that your engine is fine.

J. Hansen
1982 GS1100G

 

[gearhead13]

Pretty interesting break in procedure there, bud. Seems to me that by going WOT all the time you are trying your hardest to force air by the rings. I will be keeping my rebuilt engine well below redline and mostly no more than 1/2 throttle.

 

[Don-lo]

When I put the MTC 1055 piston kit in my 1000 about 10 years ago, I rode it nice and kept it under half throttle. I worked for a performance shop and the owner liked to say "break it in fast if you want it fast". I prefered to trust Joe Minton and Kevin Cameron, so I took it easy. I monitored it pretty closely, wanting to see the improvement, but it stayed low, 120 psi, past 500 miles. I gave up checking and thought maybe the hone job wasn't good. I think I checked again around 800 miles, and still no better. Then I checked around 1200 miles and it was 160-170, where it still is today.

 

[SqDancerLynn1]

Part of your low #s is most likley due to the cam overlap, not that anything is wrong

 

[Dan Ruddock]

Part of your low #s is most likley due to the cam overlap, not that anything is wrong

When the intake valve closes @ BDC will have more effect on cranking presure than overlap. For a given duration more overlap will increase cranking presure. This is from webcam website. Dan

VARYING LOBE SEPARATION ANGLE​

Widen​

Raise Torque to Higher RPM​

Reduces Maximum Torque​

Broadens Power Band​

Reduce Maximum Cylinder Pressure​

Decrease Chance of Engine Knock​

Decrease Cranking Compression​

Decrease Effective Compression​

Idle Vacuum is Increased​

Idle Quality Improves​

Open Valve-Overlap Decreases​

Closed Valve-Overlap Decreases​

Natural EGR Effect is Reduced​

Increases Piston-to-Valve Clearance​

Tighten​

Moves Torque to Lower RPM​

Increases Maximum Torque​

Narrow Powerband​

Builds Higher Cylinder Pressure​

Increase Chance of Engine Knock​

Increase Cranking Compression​

Increase Effective Compression​

Idle Vacuum is Reduced​

Idle Quality Suffers​

Open Valve-Overlap Increases​

Closed Valve-Overlap Increases​

Natural EGR Effect Increases​

Decreases Piston-to-Valve Clearance​

 

[Guest]

I had 120 across the board for the first thousand miles. Now with a couple of thousand miles I'm at 130 even. My cams are degreed 110 110.
Our Wiseco pistons are not high compression.
I would worry about the oil on the #4.

That is the proper break in method. At least how I've been taught.

 

[80GS1000]

I had 120 across the board for the first thousand miles. Now with a couple of thousand miles I'm at 130 even. My cams are degreed 110 110.
Our Wiseco pistons are not high compression.
I would worry about the oil on the #4.

That is the proper break in method. At least how I've been taught.

Need to re-ring the #4 cylinder you think?

 

[Guest]

Need to re-ring the #4 cylinder you think?

Are you fouling? Running issues? What was the ring gap on the upper and lower rings? Are you sure it isn't fuel?
I'd run it.

 

[80GS1000]

Are you fouling? Running issues? What was the ring gap on the upper and lower rings? Are you sure it isn't fuel?
I'd run it.

Haven't fouled a plug yet, pulls really hard on the throttle. Plug looks sort of like #1 here, but with just a few shiny oil spots - it's not covered in oil. The motor used to use a LOT of oil earlier in the break-in (used to get blue smoke coming out the crankcase breather!) but that consumption has pretty much stopped. Think that it'll seal up given enough mileage?

 

[Nessism]

Pretty interesting break in procedure there, bud. Seems to me that by going WOT all the time you are trying your hardest to force air by the rings. I will be keeping my rebuilt engine well below redline and mostly no more than 1/2 throttle.

Read this link for information you may not be aware of. Even though the heavy throttle break-in technique goes against what most OE's recommend, there is lots of technical merit to it.
http://www.mototuneusa.com/break_in_secrets.htm

 

[Agemax]

high revving (but not red lining) and not subjecting the engine to high loads, as in trying to accelerate in too higher a gear. thats the key to running in new piston and rings.
when i worked for Honda uk we would get many high revving bikes in for their 1st, 600mile service, CBR's, VFR's etc. 2 identical bikes with the same mileage would have totally different power characteristics depending on how the owner ran the bike in.
the bike that was run in properly was free revving and plenty of power, then the bike that was run in badly, ie. not revving over 3 or 4 1000 revs and changing up as quick as possible was a complete snail.
a good thrashing for a few miles would loosen it up and the owners would immediately comment on how much difference a "1st service" would make to the bike.
we did try to educate owners who bought said bikes about how to run their bikes in properly but i suppose everyone has their own ideas as to which is the correct way

 

[trippivot]

MY racing engines get broken in by racing them WOT! after just a couple minutes of revving and idling and that is all the rings need.

Break in period beyond the first 15 minutes is a CROCK!!! from the first instant an engine is assembled and started it is beginning to wear out.

a engine broken in rough IS A FASTER ENGINE!!! PROVEN TRUE!!!

ok 80 GS1000 I think you should give me wet and dry pressure numbers

1. get the engine fully warmed up
2. remove ALL 4 plugs
3. assure the measuring tool does not leak
4. WOT during tests
5. dry AND wet comp. numbers needed to get a better idea of what is going on. ( valves or rings )

I like leak down tests but that is another expensive tool and another specific diagnosis procedure.

PM me if you like. it is winter and I have very little to do.