Compression testing dual-plug cylinders?

I know it's not KZ related, but is IT is bike, and a Kawi to boot!

I need to do a compression check on Rose's VN750 Vulcan-twin, but am not sure exactely how to do so on a bike equipped with dual-spark plugs (one for intake and one for exhaust) per cylinder.
I've heard of some drag bike KZ's that have been modded to run dual-plugs per cylinder, so I KNOW somebody out there should be able to answer this.

So how is it done?
Which plug do I remove to test (exhaust or intake)?
Do I also need to remove the opposing plug to be able to get an accurate reading?
Should I test BOTH the intake and exhaust?

I would ask about this over on the Vulcan forum, but as decent as those folks over there are, most don't seem to know a lot mechanically about their bikes = the blind leading the blind.

Any help/tips would be greatly appreciated.

Post edited by: RetroRiceRocketRider, at: 2006/05/06 14:07

its the same as a single plug engine only 1 combustion chamber just leave one plug in

btchalice wrote:

its the same as a single plug engine only 1 combustion chamber just leave one plug in

Thanks btchalice!

But WHICH plug do I leave in, or does it matter?
I'd imagine it would be the exhaust plug I would pull to test and take the reading from, just like any single plugged cylinder.

I have never heard of a spark plug for the exhust and one for the intake. They both access the same combustion chamber.
After some sixty five years in the Heavy Equipment repair and operation business have I missed something ?

it wont matter

There's no combustion-heat issue while checking compression, like there could be with the engine running, so it won't matter which plug-hole you use for the gauge.
As for intake and exhaust plugs,hwms; dual plugs help the mixture light-off faster and more evenly, especially usefull for big (therefore slow-burning) cylinder bores. It allows less ignition advance for best power, and therefore less octane. Some dual-plug systems fire both plugs together, and some have variably independent timing (a Mercedes E320 sitting in the shop I work at comes to mind). Apparently, in some situations it's beneficial to stagger the sparks from the two plugs, while in others they work better simultaneously. Dual-plug conversions are done to Kaw and Suzuki drag-bikes to improve burn efficiency and speed with various other modifications (high compression, alcohol fuels, boost, nitrous, etc.). Those fire simultaneously.

TJK:

Thanks for the information. However I was aware of this many years ago. I apologize for being saracastic.

Aircraft engines are dual-plugged, for all the reasons stated above (think 360 c.i. 4 cyl or a 540 6) but with the main one being redundancy. There are two independent ignition systems (left and right magnetos) and if one failes, you still have the other one. Well hopefully! A run-up check is to switch from 'both' to 'right' and 'left'. This is done at 1700 rpm and if everything is working right the rpm should drop to 1600 for each mag alone. Proof of the gain from having both.

You can do a compression check with either plug holes, as long as the other one still has a plug in it (like everybody else said)

I really don't think there is an 'intake' and 'exhaust' plug.. probably just one that is located near each.