I previously asked several questions on ignition timing, flywheel marks ect. I purchased a timing light that has an advance dial on the back so I can go to an rpm , shoot the TDC mark by turning the dial and read what the advance setting is. Does anyone know what the total advance should be on the GM 350Q ? RPM and degree? The the screws on internal plate on my port engine optical Sierra distributor were loose and the plate rotated all the way CC. My starboard engine has an old Mallory with a spring advance. I could read it and then adjust the port Sierra but I am leary doing this at sea… not really possible to run 3000rpm under load in the slip. Unless I don’t need to be under load?? Any advise guys.
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Captain John ... From the Mallory / Prestolite factory info for the 350 Q style dist YL 566 av . 0 degrees @ 900 rpm , 3 degrees @ 1450 rpm , 6 degrees @ 2000 rpm , 9 degrees @ 2600 rpm , 12 degrees @ 3200 rpm . Consider using a digital dial back timing / rpm lite which will have better read outs to 1 decimal point . The Sierra company is just a re-seller of distributors and does not make their branded distributors . Initial base timing on flywheel dimple of 10 degrees plus 12 degrees distributor x 2 for crankshaft rotation = 34 degrees total @ 3200 rpm
Tim
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Thanks Mark this is tremendous
Thanks for the info
As Tim stated and I reinforce. Remember when using the dial on the light that the mark is NOT TDC but rather 10 degrees BTDC. You will have to do math when timing the engine.
One of my flywheels have multiple holes, one large near TDC a smaller one at DTC? Might be due to rebuilding, changing if flywheel ?? I am going to pull plugs and rotate the engine with a TDC guage I just purchased. Then know for sure which is which. Just checked and it appeared the advance at 2400 rpm went to 28°. I am going to pull the Sierra distributor and put the internal advance plate mid slot and see what I get. It may take installing and pulling the distributor several times to get it right but so it goes with boats!!!
Captain John ...... To review your 350 Q flywheel timing mark comments . There is only ONE TIMING MARK dimple on the 350 Q flywheel . The timing dimple is on the flywheel side edge of the flywheel and is 10 degrees advance and also is stamped with a letter L for left hand " port rotation " next to the dimple . The starboard flywheel is stamped with a letter R for " right hand rotation "next to the dimple . The other HOLES you mentioned on the flywheel face are balance locations NOT TIMING MARKS . The Sierra marine distributors do not have the correct timing advance curve for your Chris Craft engines . The distributor timing advance curve from Sierra products is a " generic curve " that the contractor / supplier specs for Sierra .
You are heading to uncharted shallow water with the wrong timing advance curve ! (Detonation )
Tim
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Yes I heard the rattle. I think I eill just put the old distributor back on. The engine was cutting out because the Mallory electronic coil was mounted on the exhaust Manifold( that’s what hsppens when you hire sn expert). Thank you for the explanation on the multiple holes. I have never seen any letters stamped. I will try to get a photo of the hole that is closet to TDC. Knowing that it is a 10° degree advance mark and not TDC helps. Should my timing light be on zero when I line up the mark on the pointer? Them run the rpms up and dial the mark back in to confirm degrees of advance? Thecstarboard engine is running the Mallory YL539AV. I have the one for the port engine. The previous owners mechanic replaced it with the Sierra… I still have it. The advance springs were a little rusty but I oiled them up. The cap is a little suspect but I have it. Maybe the Sierra cap will figvghe Mallory Distributor???
Also I don’t find any dimples. Just large and small holes.
Captain John .... Yes set your dial back timing light to "0 ' then aim at flywheel thru timing window @ 500 rpm to adjust the correct base timing at the flywheel dimple for 10 degree initial advance . With the engine off consider rotating the engine flywheel thru the timing window using a large flat blade screwdriver on the starter ring gear to locate and mark the timing dimple . Be aware of Sierra distributor caps that are made offshore for them .
Tim
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Yes I have tried to get info on the Sierra product… the distributors have no clue. Unfortunately it looks likevthe took over Mallory. Any alternatives ? Can I still get ghe clam shell caps for the Mallory? I am unclear how you are suggesting turning the fkywheel? You nean remove the cover?? I have hull #1 out of the Chattanoga plant and the engine room is a foot shorter than later builds. In addition the previous owners put the start batteries and strainers in the alley between the the engines. I can’t even get to my thru hull shut offs, my wife has to sqeeze in therd to work the valves. I am current trying to design some extentions to be able to turn them from under the sette and in the “broom” closet.
So I am down to where to get replacement caps for the old Mallory YL539AV distributor or a replacement that will work with the Mallory electronic coil. The Mallory distributor is optical, the Sierra is magnetic. I can see the spring advance plate inside the Mallory, the Sierra is a mystery. Any ideas will be appreciated. The engines are reported rebuilt to the flywheel marks are an unknown. I now have a TDC guage but striping off everything on the front of the engine to get the cover off is not going to happen on this boat with the engine in the boat. Anyway to calculate 10° advance thru the cover window or with the TDC guage?
So I am down to where to get replacement caps for the old Mallory YL539AV distributor or a replacement that will work with the Mallory electronic coil. The Mallory distributor is optical, the Sierra is magnetic. I can see the spring advance plate inside the Mallory, the Sierra is a mystery. Any ideas will be appreciated. The engines are reported rebuilt so the flywheel marks are an unknown. I now have a TDC guage but striping off everything on the front of the engine to get the cover off is not going to happen on this boat with the engine in the boat. Anyway to calculate 10° advance thru the cover window or with the TDC guage?
Here is the Sierra Distributor the previous owners mechanic installed using the Mallory electronic coil
18-26311-2
Sierra
ELECTRONIC DISTRIBUTOR, GM V8
FITS: GM 327Q AND 350Q ENGINES
REPLACES:
MALLORY YLM566AV
CONVENTIONAL ROTATION
FLAT CAP DISTRIBUTOR
MADE IN CHINA
STD. PACK
210723
Captain John .... There is NO TDC MARK on the 350 Q flywheel only a drilled dimple @ 10 degrees ADVANCE & marked with the stamped letter L for lefthand rotation or R for righthand rotation next to the dimple . You can source the distributor flat caps # MA - 221 B from Summit Racing or other retailers also . Find the timing window on front cover that looks down on the flywheel side edge & ring gear area .
Tim
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Ok I have been using a window on the face of the flywheel… I will take a picture today when I find TDC
So today I pulled my plugs and with my trigger bumped the engine and found this small dimple. I removed the pointer for a better shot. I used my small USB camera and found the piston just shy of TDC. I need to move my distributor a couple teeth to bring this into view. I will see if the engine runs any better.
The window is on the front of the engine nearly centered. Does that look like what I have been missing?
Yep!!
One last question… the dimple comes into view twice with the distributor rotor 180° apart. The engine won’t run up to 3k 180 out right? It might back fire but it won’t run from what I remember..
The rotor should point toward the #1 cylinder when at TDC.