Timing and Sync of Merc Inlines (to 1988)

[tashasdaddy]

Re: Timing and Sync of Merc Inlines (to 1988)

Wayne, you have to remember it's in the faq. i've refered many to it in your absence. thanks for the great effort to create it.

 

[merc850xs]

Re: Timing and Sync of Merc Inlines (to 1988)

Thanks CC.

One more thing. When doing TDC pointer should flywheel be turned with normal rotation or against? Way I see it is it would be loaded correctly when turned against or opposite normal rotation. The reason I ask is, if done both ways the start of flat spot (as it goes over TDC) one way is start of flat spot other way, a difference of approx 6 degrees. Due to big/little end wear I guess. Thanks.

Dave

 

[Clams Canino]

Re: Timing and Sync of Merc Inlines (to 1988)

Rock it both ways.... TDC is in the middle. Find your average "guess" out of 10 tries... TDC will be within one degree. If the difference is astounding, err to normal rotation.

-W

 

[Scaaty]

Re: Timing and Sync of Merc Inlines (to 1988)

I noticed an interesting thing today Clams, I disconnected my throttle cable and operated the arm by hand but it did not spring back to the idle position, only the the most advanced stage before the carbs open. Is this normal, whoever had the engine before me apears to have sprayed some thick treacle like greaze over the distributor, it may just be an anti corrosion grease or something but it seems to be creating a smooth resistance in the throttle operation.

Not sure what motor we are talking here, but on my just put together from the crank up 72 inline 6 (by a 40 year inline Guru to..Clams, you two would get along and BS for DAYS!), I was told to have PRELOAD on the throttle cable to hold the Distributer against the idle stop. When I picked up the motor, and thought I had enough, it started to idle raise while warming. I cranked another 2 turns in today, and perfect. There are no return springs...cable does all the work (Clams..great work and post!). Heres a pic of the beast I put together this winter (jeezz, an island, beer, pizza, and inline Tower of Power's,..HEAVEN!)​

 

[merc850xs]

Re: Timing and Sync of Merc Inlines (to 1988)

Way I see it is it would be loaded correctly when turned against or opposite normal rotation.

Dave

Ok, I retract the above statement. Thought about it some more, can be seen in scrible attached.

Further, I have seen a method used on rotax engines where a dial indicator is inserted in plug hole to measure piston travel. Crank is set to TDC and a pump is used to create a pressure or vacuum above piston pulling piston up and down. The measurement taken is total of the radial play in conrod bearings. From memory 5 thou max total is allowable, 3 thou for big end and 2 for small. If it is outside 5 thou both bearings are worn or one is very bad.
I checked a 2 stroke bike manual and 3-4 thou for big end only is stated.

I have repeatedly done cyl 1 and 2 (only ones I can get at for the moment) on the 850 and get consistantly the same results, they are as follows:

No1 Flat spot/bearing uptake=6 degrees, total bearing play=9-10 thou
No2 Flatspot/bearing uptake= 3 1/2 degrees, total bearing play=3 thou

Looks like No1 is suss.

Like to hear your thoughts on the method and the results.

Dave

 

[merc850xs]

Re: Timing and Sync of Merc Inlines (to 1988)

I'll try and get something you can read up

Dave

 

[Scaaty]

Re: Timing and Sync of Merc Inlines (to 1988)

CC: I have a 75 mercury 850, I have the max advance set at 27 degree. After reading your post
I wonder if I should set it to 21 degrees. What will this do for the motor?

21 will keep those little holes in pistons from forming..(OUCH at 27!)..ya been either lucky, or running the best premium gas (might have been OK in the 70's, but the gas now is crap compared to then)​

 

[merc850xs]

Re: Timing and Sync of Merc Inlines (to 1988)

I have put up a some what better attachment in previous post.

The timing marks on the flywheel of the 850 have been rubbed off. Another method of finding where 21 degrees would be, without having to count the teeth on flywheel is as follows:

Measure diameter of flywheel, across outer face where timing sticker would be. Then use math to calculate. My 850 flywheel measures 208mm.
208 x 3.142 divided by 360 = 1.81mm per degree.
21 x 1.81 = 38.12mm

21 degrees is 38mm measured from TDC.

Dave

 

[Clams Canino]

Re: Timing and Sync of Merc Inlines (to 1988)

Yes.. that also works.

-W

 

[stroyer]

Re: Timing and Sync of Merc Inlines (to 1988)

hi from Denmark.
just did the Timing and Sync. on my 6 inline 115HP early 80.
mounted on a 14 foot fletcher arrowflyte bravo
now it runs like a clockwork.
thanks for the good explanation.
now i just have to find a wiring diagram for my tach.
any links ?

 

[83 Merc]

Re: Timing and Sync of Merc Inlines (to 1988)

1983 80 hp Merc, manual says to set maximum timing @ 27* BTDC. I've been scouring these threads to try and understand the process of link and sync and have read that 21* is the way to go, despite what the manual says.

Just so it's clear to me, is setting this different adjustment based on the new blends of gas today and the wear and tear on an old motor? For this motor, which max timing should I go with? Thanks guys.

 

[diaric]

Re: Timing and Sync of Merc Inlines (to 1988)

21 will keep those little holes in pistons from forming..(OUCH at 27!)..ya been either lucky, or running the best premium gas (might have been OK in the 70's, but the gas now is crap compared to then)​

explains it pretty much. gas today is not as good.

 

[m.a.walgren]

Re: Timing and Sync of Merc Inlines (to 1988)

i have a 1972-3 merc 115 ,when i bought it the rotor was out of it because the bottom racer berring went bad . i replaced it along with the berring and reinstalled the dist. then i installed a carb kit . my question for clams is , when i get my motor running, the idle keeps increasing. (i havent set the the timing yet) by doing the tining and sync will this help ? im not sure that i got all the throttle pickup clusters on top of the carb asembly right ,does anybody have a picture ? (where the asembly, and the pickup go together) plus ,does the bar that operates the individual carbs have to be adj. in a certin way.

 

[Chris1956]

Re: Timing and Sync of Merc Inlines (to 1988)

If the idle speed increases as the motor warms up, it could be picking up cylinders. This should be a tuning issue. The cluster on the top carb should just touch the dissy arm at the idle pickup timing spec (usually 3-4 degrees BTDC). When the top carb is fully closed, loosen the cap screw on the mid and bottom carb and close the throttle plates. Adjust so they all open at the same time, and thay will synch them. Now follow Clams link and sync procedure.

 

[thinksun]

Re: Timing and Sync of Merc Inlines (to 1988)

Question re: Clams Canino set up

My engine info

I have a 1986 Mariner L6 rebuilt last year, new electronics, new fuel and clean everything. I did the BB and vent jet removal trick on the economizer circuit as posted here, left the idle stabilizer on. Idle fuel screws set 1-5/8 turns except for bottom carb which is 1-1/2. Boat is a restored 71 Sidewinder Lo-Pro with a 23 SS prop turning 5400 rpm loaded at 59 mph on dream-o-meter. The idle is 900 and drops to 550/600 in gear. Runs well

Question

If I change idle timing from 6 deg ATDC to 4 deg BTDC as per write up will I see a smaller spread in idle drop from neutral to forward. Are there other benefits to 3-4 deg BTDC that I would see.


Appreciate your response, like to ask before I fix something that's not really broken. I strive for perfection though.

 

[Chris1956]

Re: Timing and Sync of Merc Inlines (to 1988)

That is a nice looking boat. It looks a lot like my '74 Avenger. I did not know that Sidewinders came w/o windshields.

I do not have an answer for you on the idle timing issue. The 3-4 degrees BTDC Idle pickup timing is standard on the inline sixes. The idle timing on my '93 135HPV6 is 4 degrees ATDC, for some reason. The purpose of the idle timing is to synchronize the advance to the carbs. With your current setup, you are running a bit retarded in relation to where it should be, at a given throttle opening, until you hit max advance.

 

[thinksun]

Re: Timing and Sync of Merc Inlines (to 1988)

Thanks, the boat is like original as the low profile version without windshield.

Here are the specs I have from my Mercury service manual re timing. I wonder if the 115 idle timing spec is different because only the 115 has the idle stabilizer. Maybe if one by-passes idle stabilizer, then the BTDC spec of the 90 would be used-- did I just answer my own question? Thanks, Bob



Here's what I see when I start out.

 

[Chris1956]

Re: Timing and Sync of Merc Inlines (to 1988)

Well the excerpt from the Merc manual appears to be quite clear. The 115 specifies the retarded idle pickup timing. I do not know why. My Merc 1500 was a distributor model and specified the 3-4 BTDC idle timing.

It may have to do with the idle stabilizor. My Merc did not have one.

BTW - My Avenger was originally the same color scheme as you Sidewinder is. I have now painted it off white with teal accents. Not as much fun as the metalflake, but a whole lot more durable....

 

[redjmp]

Re: Timing and Sync of Merc Inlines (to 1988)

Perhaps the info in that service manual is intended for engines with hp rated at the head.
The later day 115 is probably not covered by that spec.
But, surprisingly enough my "86 has a sticker that specified 6*ATDC though it refuses to run well when set up that way.
I did remove the idle stabilizer though so maybe that has something to do with it.

 

[thinksun]

Re: Timing and Sync of Merc Inlines (to 1988)

Perhaps the info in that service manual is intended for engines with hp rated at the head.
The later day 115 is probably not covered by that spec.
But, surprisingly enough my "86 has a sticker that specified 6*ATDC though it refuses to run well when set up that way.
I did remove the idle stabilizer though so maybe that has something to do with it.

That's from the 86 Mercury service manual, not a Clymer either. I am now sure if you disconnect the idle stabilizer idle must be set 3-4 BTDC.