More about Iridium Plus

Installed a new set of Iridium plugs (NGKBPR8EIX) in my 83 900 Seca last fall. All was well. Was out a few times this spring and running great. Went to warm up the engine prior to doing a oil change and #1 wasn't firing. Changed the oil and ran the bike to circulate and #1 still not firing. Went out a few days later to investigate and no start at all.

Put a tester on Cyl #1 and was getting a good spark but pulling the plug and no spark visible. Same thing with Cyl #4. Looking closer I did see a spark way up in the plug between the insulator and the plug body. Nothing at the tip. The all plugs were quite fouled. Installed a new set of plugs (NGK BPR8ES). And it fired right up. I figured I had about 350 miles not the iridium plugs.

Is this typical for Iridium plugs or am I looking at a weak ignition system/bad ground/bad plug wires?

Also while I have your attention. Did a compression test while in there. 110 PSIG for 3 cylinders but 125 on Cylinder 2? I assume 110 is about right and i might have something going on with Cylinder 2?

All help appreciated.

Bob C.

 

Either they are not genuine NGK or, more likely they aren't getting hot enough to self clean. Those iridium plugs are normally good for 100,000 miles.

 

Cylinder Compression Gauge:

Yamaha recommends that you perform a compression test every 5,000 miles or so, and that you should record the readings, per cylinder, for future comparison and evaluation. The acceptable readings (specified at sea level) are as follows:

To do a compression test properly, you should first make sure all of your engine valves are properly adjusted to their recommended clearances, as valves that are too "tight" (not enough clearance) will allow the intake or exhaust valve to be open more than is necessary, or at the wrong time within the compression stroke cycle, thus bleeding off compression that would otherwise be developed.

http://www.xjbikes.com/forums/threads/compression-test-xj650.113151

Do not use thread adapters or the like on your pressure gauge, as the added volume of air space within the adapter will reduce the indicated pressure readings.

a) make sure the engine is warm (at operating temperature).

b) remove all spark plugs, and then stick the plugs back into their caps and make sure the plugs are grounded to the cylinder head (or even better, disconnect your TCI unit).

c) remove the airbox filter lid and the air filter.

d) make sure the battery is FULLY charged, and remains so throughout the course of these tests! It is actually recommended that for purposes of compression testing that the TCI be un-plugged and jumper cables to a large capacity battery (i.e. car battery) be used to make sure that the cranking speed remains pretty constant between each reading. Slow or sluggish cranking speeds will reduce the indicated compression pressure. Yamaha specifies their compression pressures at 300 rpms (which is why the battery needs to be in good shape).

e) open the throttle FULLY and keep it open during testing.

f) crank the engine over until the needle stops advancing.

g) Let the starter cool down for a minute or so, then do the next cylinder, etc..

h) If the readings are below spec, then shoot about a teaspoon of motor oil into each cylinder, turn the engine over a few revolutions by hand or with the starter (to spread the oil around), and then re-test each cylinder using the above procedure.

i) compare the two results and analyze.

j) keep all of your figures, and note the date and mileage from your odometer, so you can compare the next time you take readings (every 5,000 miles or so).


The specified compression pressures should be:


XJ900 engines:
Minimum: 114 psi
Standard: 142 psi
Maximum: 171 psi
Max. variance between lowest and highest: 14 psi




NOTE: for readings taken at locations that are above sea level (ASL), the following correction factors should be applied to the readings that your gauge obtains:

- 500' ASL, multiply your readings by 1.013 to get a "true" compression reading.
- 1000' ASL, multiply your readings by 1.029 to get a "true" compression reading.
- 1500' ASL, multiply your readings by 1.042 to get a "true" compression reading.
- 2000' ASL, multiply your readings by 1.060 to get a "true" compression reading.
- 2500' ASL, multiply your readings by 1.072 to get a "true" compression reading.
- 3000' ASL, multiply your readings by 1.093 to get a "true" compression reading.
- 3500' ASL, multiply your readings by 1.103 to get a "true" compression reading.
- 4000' ASL, multiply your readings by 1.126 to get a "true" compression reading.
- 4500' ASL, multiply your readings by 1.136 to get a "true" compression reading.
- 5000' ASL, multiply your readings by 1.160 to get a "true" compression reading.
- 5500' ASL, multiply your readings by 1.172 to get a "true" compression reading.
- 6000' ASL, multiply your readings by 1.196 to get a "true" compression reading.
- 7000' ASL, multiply your readings by 1.233 to get a "true" compression reading.
- 8000' ASL, multiply your readings by 1.272 to get a "true" compression reading.


Also, be aware that barometric pressure differences (during testing events separated by more than just a few hours) will cause changes in indicated compression readings. Atmospheric pressure can vary significantly over time at the same altitude, due to weather systems….you hear this on weather reports, where the forecaster is talking about “High” and “Low” pressure systems. Basically, higher atmospheric pressures translate into higher indicated compression pressures. Although it is rarely of major consequence, in order to be "dead-nuts" accurate you should also record your local barometric pressure at the time of each test. If you measured compression on a day when it was 1030mbar and observed 150psi, and then took a measurement later in the week/month/etc. when the ambient air pressure was only 990mbar, that’s an environmental air pressure difference of about 4%, and assuming nothing else had changed you would then read a 4% less compression pressure of only 144psi......i.e. lower ambient air pressure results in lower compression pressures in your engine.


But don’t overlook the fact that the individual test gauge being used is probably the greatest variable. Some compression gauges are just not very accurate to begin with (basically, and within reason --- and just like with most tools --- the more it costs, the more accurate it will tend to be). Also, try to keep the hose on the gauge you are using as short as possible….the space inside the hose adds to the volume of the cylinder, as lowers the compression ratio a bit, and thus reduces compression pressures.

And in case you are interested, here are the standard compression ratios for the various engines:

XJ550: 9.5-to-1
FJ600: 10.0-to-1
XJ600 Seca II: 10.0-to-1
XJ650 (except Turbo): 9.2-to-1
XJ650 Turbo: 8.2-to-1
XJ700 air-cooled: 9.5-t-1
XJ700-X and XJ750-X water: 11.2-to-1
XJ750 air: 9.2-to-1
XJ900: 9.6-to-1
XJ1100: 9.0-to-1
XS1100 9.2-to-1

Note that the XJ650 Turbo engine has a much lower static CR than all other engines……logically so, since it has a device (the turbocharger!) that raises the atmospheric pressure of the incoming air charge. Also of note is the rather “sky-high” CR of the multi-valve Genesis engines in the water-cooled “X” engines, which is also one of the keys to their vastly increased power output.



Now Analyze This!:

1) If one or all of your cylinders are too low in pressure, it means that:

a) you did the compression test incorrectly

b) the tester gauge is inaccurate, or was not used properly.

c) your engine has piston ring, piston wall, or valve leakage problems.

d) your valve clearances are too tight, and should be adjusted, or the cams are out of time, or aftermarket camshafts have been fitted that have altered the camshaft timing.

e) if a cylinder or cylinders have NO compression at all, that typically means your piston has been catastrophically damaged (i.e. a hole in the piston crown, broken piston, etc.)

f) if a cylinder or cylinders have good compression that rapidly "leaks away" (best determined by the use of a Leakdown Tester gauge as listed further below), this points to burned or otherwise problematic valves.

In order to further analyze a low-compression condition, you should squirt a small amount of engine oil into the suspect cylinders (about a teaspoon), crank the engine over for a few revolutions to spread the oil about, and then re-test those cylinders. NOTE: if cranking the engine over with the starter motor, you should place a rag or similar over the spark plug opening, or the oil you just introduced into the cylinder may spray out forcefully (into your face, onto your engine, all over the place……….!).

g) if the compression pressures RISE by a large amount after the infusion of oil, then this typically means that the pistons, piston rings, or cylinder walls are damaged or worn in some way(s). However, be aware that if you introduced a significant amount of oil into a cylinder (1 teaspoon or more) when conducting this test, a small rise in pressure may occur, and it may instead mean that your valves are the problem, since the introduction of that much oil in a small cylinder will naturally cause the compression to rise.

h) if the compression pressures do NOT rise after the infusion of oil, then this typically means that the valve seats or faces are worn, or a valve is hanging up within its guide, or your valve clearances are way too small (thus keeping a valve open all the time throughout the entire compression stroke).

i) if two adjacent cylinders (cylinders 1 and 2, or cylinders 3 and 4) have low compression, and the oil treatment produces no greater pressures, this points to a damaged cylinder head gasket, warped head, etc.

j) it can be very useful to introduce 20-30 psi of compressed air into the cylinder (thru the spark plug hole) to help identify the source of low compression: the escaping air can pinpoint the source of the leak (air hissing out of the intakes or exhaust points to valve problems, while air escaping thru the crankcase breather indicates ring-seal issues).


Of course, many other situation may cause low cylinder compression, including valves that are out of adjustment (too tight, thus holding a valve slightly open all the time, losing compression), cracked pistons, cylinders, or cylinder heads, but those situations are the not all that common.

 

Even new spark plugs can be bad. Sounds like you got a couple.

 

But new NGKs? Two of them? Somehow I suspect they were Chinese knock-offs.

 

I tend to agree.