Timing question

We bought an RV7 last summer and it is due for an annual now. It has a Superior XP-IO-360-B1AD2 engine with a slick and lightspeed. It is timed right now at 20 degrees and engine runs great.

Everything I have read says the timing on 360?s should be 25 degrees. Question is should we change the timing to 25 degrees if the engine seems to be fine there or do we change to 25 degrees?

Thanks!

I think it depends on your compression ratio.... less than 8.7:1 and we use 25 BTDC, 8.7:1 or higher and we use 20 BTDC.
The XP-360 is available with 8.5:1 standard and options for 7.2:1 and 9:1 compression ratios. Perhaps you have 9:1?

If you have the LSE Plasma with the magnet ring installed on the flywheel, the factory installed magnets are installed in specific locations for either 25 or 20 degrees.... you can't change that without changing the magnet ring. If your LSE Plasma ignition has the Hall Effect Sensor that mounts in a magneto hole, then you can change the timing (its in the installation manual).

I should have provided more detail. I have standard compression at 8.5:1. I also have the Hall effect with sensor in the LS Plasma.

Given that, is there any benefit to changing to 25 since it seems to be doing fine at 20 degrees? I assume it was timed like that for a reason but just can?t figure out why and don?t want to mess anything up.

What does the data plate list for timing?

RedRaider94 said:

I should have provided more detail. I have standard compression at 8.5:1. I also have the Hall effect with sensor in the LS Plasma.

Given that, is there any benefit to changing to 25 since it seems to be doing fine at 20 degrees? I assume it was timed like that for a reason but just can’t figure out why and don’t want to mess anything up.

Click to expand...

Given a parallel valve, standard compression engine, it should not be possible to harm anything by resetting base timing to 25 BTDC. Benefit is something you'll need to measure. The usual approach is to fly simple three leg true airspeed runs at various altitudes, before and after the timing change. The values are plugged into what we have come to know as a NTPS TAS spreadsheet, which eliminates the effect of wind. If you want to do it, speak up, as there is plenty of help here.

RedRaider94 said:

I should have provided more detail. I have standard compression at 8.5:1. I also have the Hall effect with sensor in the LS Plasma.

Given that, is there any benefit to changing to 25 since it seems to be doing fine at 20 degrees? I assume it was timed like that for a reason but just can?t figure out why and don?t want to mess anything up.

Click to expand...

The short answer - yes, there is something to be gained for running at the appropriate 25 degrees BTDC, especially if you are striving for most efficient LOP cruise.

Perhaps the previous owner was trying to achieve additional detonation margins to run mogas - but I?m just guessing.

As this is a new plane to you, recommend you carefully read the LightSpeed manual on Hall Effect sensor inspection and maintenance. The oil seals tend to leak with time.

Carl

Because you have a split system (one EI), this makes a straightforward answer tough. In general, the mag should be timed to the data plate value and the EI's curve should drive optimal PCP/crank angle. Even with a canned curve from the EI though, you are going to need to burn some gas and take data if you want it optimal for your particular airframe/engine configuration.

Carl, interesting that you mention the oil seals. I have noticed a very light amount of oil on the rear of the engine housing. Not much as it is very light but it is there after wiping it down and then flying. Can?t find the source anywhere but never thought about that as a potential area of concern.

I assume the seal is a gasket but not sure where I can get one. Any ideas? LS manuals talk about inspection but doesn?t discuss what is needed if you find an oil leak.

Shawn,

The Hall Effect sensor has an seal ring on the rotor shaft to keep accessory case oil from entering the sensor. If memory serves, the LightSpeed manual calls for annual removal of the sensor and taking the top cover off to check for bearing wear and for oil inside the sensor. Easy enough to do.

Klaus got very annoyed with me when I tried to purchase replacement seal rings from him after both of my sensors seals started to leak at about the 300 hour point. He refused to sell me the replacement seals but did offer to repair the sensors themselves for what I considered an unreasonable price.

As this was just the last many issues I had with this product I removed them and replaced with pMags (now 700+ hours of flawless operation).

I don?t want flames as I know there are builders who have a lot of hours behind LightSpeed. I?m just sharing my experience.

Carl