20H Timing

[JESSE74]

What should the timing be set at for an old merc 20H?

[f8andbethere]

It depends

Like anything else, it depends on how the motor is set-up. It's been 25 years probably since I played with one and my book is not handy. If someone else does not post I will drag my tail out to the garage and find a number for you.
f/8

[G Stillwill]

For a hydro we time at .345 with a converted popper and .400 with a unconverted one for a runabout it would be some what lower. When you go to pull it over pull like you mean it or you will have really sore fingers This is with a dial indicator not a degree wheel.

[bill giles]

I never set it higher than 275-280 but make sure you are at 180 degrees from each other. Also, set the 1st set of points at .15 gap. It worked well for me for many years! I know those who set the timing over .300BTC but you risk damage and gain little.
Bill Giles

[STEVE FRENCH]

I run my 2-cyl mercs (kg-MODS and 20H's) and my 22-OMC's like George Stillwell , around .320-.350.....BUT!....if you are running a filler block to a pipe or commode conversion.......I have found (the hard way)...that you must "float" the filler block in red silicone and run 1-2 extra side cover gaskets so the filler block does>> NOT<<< exspand from the higher heat at this timing,....and "PINCH" the cylinders and STICK!
Bed it in block with a bead of red silicone and find a light that fits bore and look for open spots (or if assembled, just make sure (best ya kin) that it seals port opening). then take a straight edge across filler and cover gasket area. Filler must be flush or slitely below side cover gasket area !!!!
If flush or less than a credit card thickness from flush (Cover should not "ROCK" on credit card), run a extra gasket.
Let filler dry over night..Trim excess sealer from ports with a scal-pul (Or model'rs knife-or best ya kin,..... with a "toad-sticker"/cat-fish skin'r/switch-blade/etc )...then put a good bead of silicone on surface of filler that meets side cover to seal to cover-pipe/ or commode conversion cover.
This should allow a dry filler to EXSPAND with out stick'n cyls above the .150-.285 timing setting "Iron Fist"/Merc reccomended when the commodes started stick'n when they first came out 50? years ago
(PS----I/ME/MYSELF.....do NOT use the copper o-rings that were used when high-temp silicone was-NOT avail..........I Think the filler needs to float with out contact...or metal-to-metal........There may be some... "Mate'n of elephant " ...argument over this but............. )

Have also found that 20H's have 2-different filler block dimensions depending on vintage....... (Thanks Iron-Fist!)
Newer 20H castings that say....... "hurricane"...(Like a Mark-25) ......have more water jacket area to run cooler? and the filler blocks are not as thick....
If you get a early filler it will take some "Widdle'n" ..... to fit flush or below in a late cyl....
If you have the opposite senerio.........LOOK FOR ANOTHER $50-100 filler!

I have one highly MODified 20H cyl from my OMC builder-Rick Morris, that he and Dudley Malone sleeved and cut some huge two-port windows in (Like a Yamato)........they used Devcon to bed the filler in it years ago....Rick told me this cyl ran like a raped-ape till it stuck........I aquired a couple NOS.030 O/S pistons for it a couple years ago for over $325
The filler is still bedded very well and is close to flush.....so I HOPE to run an extra gasket and also going to drill a couple- "PEE-holes" through inside water jacket passage.........so it "water cools" the filler from both sides. This might be a little tricky but since my tower has plenty of drain holes in it .....it should not fill filler area with water.
Have also been in contact with Mike Petty in Florida, and he now offers a OMC-"A" CDI conversion for these.
I will start with the old Paelon Mag and ...HOPE ... it provides enough "Fire-in-the-wires"....... to keep it "lit" for three laps, but hope to have all my 2-cyl MODS runn'n OMC CDI.....soon/someday.
Converted one of my 22-OMC 25 MODS last year and found--the HARD WAY that the .340-.360 BTDC..... I run with points is too high with the CDI......going to back it down to .300-.310 and start over test'n and watch'n plugs..........

These ol motors are the ul-ta-mit >>>TEST<<< of a persons patience/fortitude!!!!!!! .........and will only LAUGH at ya ...if you .........let them test it......but when THE-plan..
.. "I LOVE-IT when-a-plan... all comes together" ("A-TEAM" guy/George Papar?)...................the ride is SWEET!
Especially if the Hot-Rod A-MODS........JUMP-the GUN!

Good luck and keep us POSTED!

19P "NEVER READY RACE'N"
PS-I have a A-MOD legal 20H from Jim Roberson / "Roberson Custom Cycle" (Harley's) in my motor box for sale. will be at Franklin on display at my trailer......$1850?
Or call Jim at 814-694-3225 (Maybe a serious $$$$ ....offer will git to test it Friday...buyer or me drive'n?....... )
.

[JESSE74]

Hey guys,
I am settin' the 20H up on a standard H tower to run on a runabout. Also, it have to do some idling when I run on my local lake, there is a small bay maybe100 yards I have to get through before i open it up. I could only find specs for Mark 25 and was .235 so that's what I was gonna go with, should I go higher?

[jsilvestri]

Jesse, I've always set my 20H timing at 265 for both the runabout and hydro. Good luck with your project. What type of runabout do you have? Is this project for fun or are you planning on racing the rig in AMR this summer? My block just returned from being bored and the motor should be ready for the Zanesville Mod Nationals. See avatar for a pic of my rig.

[STEVE FRENCH]

Hey guys,
I am settin' the 20H up on a standard H tower to run on a runabout. Also, it have to do some idling when I run on my local lake, there is a small bay maybe100 yards I have to get through before i open it up. I could only find specs for Mark 25 and was .235 so that's what I was gonna go with, should I go higher?

(Start) at .235..........then watch yer plugs...........once yer comfert'able with motor....go to .265.............ck plugs adjust carb...........run it........then .285...ck plugs/adjust carb.........etc.....etc......
When it won't start ........with-out crater'n starters ...or your arm looks like- "POP-EYE the Sailer's" ......yer close?

Post some pics....... >>>>>>>> Have Fun........

19P

[bethann]

20-H Timing

Stover Hire set his timing at 285. That seemed to work well for him.

[JESSE74]

Thanks for the great advice guys! Runabout is an old Broccoli, one of the first roll chines. So far it has been just a lake play boat, but I may try competing with it sometime. It would fit in to AMR with the H tower? Nobody has an extra tilt pin they could part with do ya?

[G Stillwill]

Tilt Pin still can be bought from Mercury new part number.17- 56373A 2 PIN-KIT $12.80

[Mike 41P]

20H timing

You are getting an earfull, aren't you.
Set your 20H at .265 and check and adjust them individually.
Get the gap of your top point set at 15
Move the plate to set the top advance at 265
Switch to bottom and check it, it probably will be off more than you expected
You can't move the plate now, use the gap adjustment to get the bottom to 265 (or 260 to 270)

I've run as high as 350 but it gets hard to start, won't idle, needs a lift to get going, etc, etc.

265 will be 'safe' and a lot easier to start and get planned off

Mike T

[DeanFHobart]

Stock Timing

The stock timing was .265" BTDC.

[JESSE74]

So who is really right? Just kidding, what I did was set at .250" BTDC and .18 on #1 cyl. and it ended up a snug .18 on #2 cyl. In the process I noticed I could probably use some new points also, so i'll try this setting then replace points and try again.

Steve, don't think I need anymore old mercs. right now, I'm really concetrating on getting started with a yamato 80 in 20 hydro this spring.