Ignition Timing on a chevy 454.?

[fgutie35]

I set the ignition timing on my Elandan, because I removed the A.I.R. system and I heard the timing goes off when you do that. Sure enough, it was 12 degrees BEFORE. I checked the Emissions Label on the Air filter cover, and it specified 4 degrees@ 700RPM's, but it did not specified BEFORE or AFTER. My valance marker has this markings from left to right (or up to down). "12, 10, 8, 4, 0, 4". When I moved the distributor clockwise, it went down to 8 BEFORE and the engine went down on RPM. Then I moved down to 4 BEFORE and the RPMs got even lower. I tried to go to "0" but it sounded like the engine was going to stall. So I figured it should be at 4 degrees BEFORE. Am I right? or is it suppose to be at 4 degrees AFTER?? i??

[RV Mech Tech]

fgutie35 -if you are standing in front of the coach looking at it, where is the timing mark tab on your timing chain cover? - is it at the 12 o'clock position or somewhere between 4 o'clock and 6 o'clock?  - also the timing will be 'before TDC'  on an automatic trans- usually the vacum advance is disconnected and plugged while doing this  depending on the procedure on the emission label for you specific application - you are setting the 'static' timing (mechanical timing ) first then with the vacum advance reconnected it will bring up the timing and rpm depending on the application.

[fgutie35]

Ok, so then it is 4 degrees before TDC. Great! If I'm infront of the engine, the marking tab is at the 4 O'clock position. I have to plug the timing light at plug wire 5 or 8, but since the tab is on the driver side, I put the timing light on plug 5. I did disconnected the vacuum like it says on the opeators manual. I had seen on more than one Hot Rod website, that there is another way to set ingnition timing for optimum performance on the 454, but the instructions are rather lenghty and I will need like two other people to help me, and I got no one but me myself and I. As it is, I had to go under the MH like four times to finally hit the bulls eye on the 4 degree mark!

[RV Mech Tech]

fgutie35 -yep -working on motorhomes is a lot of fun!! - you can also set the timing while driving on the road with someone adjusting the distributor while you drive- I have found that if you have an older engine with any amount of miles on it  you have to consider the wear (stretch)  in the timing chain and other parts such as the distributor, camshaft  and crankshaft gears ,  and worn  parts for the vacum advance  inside the distributor -all of this wear adds up so that even if you set the timing to the specified  4 degrees and do everything according to the emission sticker you may still have a problem with pinging or lack of power - this is where a road test and setting the distributor on the road may be required - also the octane rating and quality of the fuel in your tank, and  ambient temperature affect the engine and timing  as well - with computer controls the computer makes all the adjustments to compensate for any problems but on the earlier  non-computer engines  you may have to do a little more work to get it where you want it-  on your 1988 MH you may have a small control module that affects the ignition timing and it is tied in with a knock sensor that will retard the timing if lets say you get some bad fuel - you will find this on a lot of late 80's 3/4 and 1 ton truck engines  and this is not an engine management system but only an ignition control system - also any vacum leaks anywhere will definitely affect the timing and operation of the engine just like the new engines so make sure you do not have any - a vacum gauge is a valuable tuning tool along with the timing light and when connected to direct manifold vacum will indicate if you any leaks or other problems within the engine- let us know how it turns out.

[fgutie35]

Thanks for the sea of information you have given to me. So far I have not taking it for a spin, but now that you mentioned that fuel quality affects the timing, I may need to check timing once I ran out of the Premium gasoline I filled up the tank with. I usually do this to all of my vehicles to keep the guts clean. I run a full tank of premium gasoline every 10 tanks full of regular gasoline. On this case, this is the MH's first full tank$$$$.
I will let you know how it went, once I have a chance to take it out.

[RV Mech Tech]

fgutie35 - in regards to fuel quality it does not affect ignition timing but a lower quality fuel does not support combustion the same way as a higher octane rated fuel or fresh fuel  does - also the age of the fuel does definitely change the quality of that fuel - a common explanation is that the higher 'ends' of the carbon chain  (fuel chemistry- these higher ends are what support combustion in fresh fuel) tend to evaporate as well as the additives in the fuel - so if you have the timing set correctly with fresh fuel then you will get maximum power from the engine - in a non computer controlled engine you will not get the same effect with stale fuel -( the computer will change timing  to compensate for this so it will seem that the engine will be o.k.) but you notice it more with a non computerized engine - this is a big problem with RV's that sit for a long time - also  where you buy your fuel has a lot to do with it as well - when you pay top price for gas at a name brand station you are most likely to get fresh fuel - the oil companies cycle the gas reserves so that  with  gas that's coming close to a month old they will sell off to a non-name brand or generic off brand gas station to use that gas up and sell the newer batch of fresh gas to  hi volume brand gas stations ( that's why the cheaper price) -  one way to take care of this is if your RV is going to sit for any amount of time then put in gas stabilizer and run the engine and generator for at least ten minutes to make sure the stabilizer reaches the engine and genset fuel systems.

[fgutie35]

Thanks, I will consider that.