'92 Force 150 O/B problem

[pnwboat]

Re: '92 Force 150 O/B problem

Have you checked to see if the flywheel key has sheared allowing the flywheel to shift? You can check by lining up the timing mark on the flywheel at "0" degrees TDC and look at number one piston. Verify that #1 piston is actually at Top Dead Center. If not, then your flywheel has moved.

 

[Markas]

Re: '92 Force 150 O/B problem

Checked before and just checked again. With plug out a screwdriver resting on piston in #1 cyl is furthest out exactly at 0 deg. Moving flywheel even 2-3 degrees either direction causes screwdriver to move in to cylinder.

Any other thoughts?

Thanks

 

[pnwboat]

Re: '92 Force 150 O/B problem

Could it be that something in your ignition system is mis-wired? There were two types of ignition systems used on the 1992 150HP motors. Earlier units had the Prestolite system with the blue coils and CD modules. Later motors used Mercury Thunderbolt systems with the CD converter and a switchbox. Which type do you have?

 

[Markas]

Re: '92 Force 150 O/B problem

Thunderbolt. Traced trigger wires to control box - colors all line up. Checked wires to coils - colors line uo. Even switched coil 2 with 1 - no change.

Took nut off flywheel - can see key but can't see camshaft keyway to see if it shifted.

Seems like that would be what it is but best I can tell tdc is ok.

Thanks

 

[pnwboat]

Re: '92 Force 150 O/B problem

If the zero degree timing mark on the flywheel is lined up with the reference mark on the metal tab above the upper carburetor, and #1 piston is actually at TDC, then the flywheel and crankshaft are properly sync'd up.

Just want to make sure I understand you correctly. When you did the WOT static timing, it was set at 40 to 50 degrees advance BTCD? So basically you're about 10 - 20 degrees too far advanced?

I wonder if someone bent the upper arm of the tower shaft inwards towards the motor? This would have the same effect of advancing the timing because it would move the trigger assembly further in the counter clockwise direction.

 

[Markas]

Re: '92 Force 150 O/B problem

Had to come in off the lake. Yes, timing mark when timing light connected to top cylinder at wit static was 40-50 deg to left of zero mark.

Silly question: I found tdc for each cylinder and marked them on the flywheel with tape. As expected they are about 1/5 a circle apart and are evenly spaced.

But starting from the top cylinder as number 1, the firing sequence when rotating the flywheel cw is 1-5-2-3-4. Is that right?

 

[pnwboat]

Re: '92 Force 150 O/B problem

Yes that is the correct firing order.

After thinking things through, I'm sure your problem is with the linkage between the tower shaft and the trigger assy. Something is bent or not assembled correctly. Basically you have to rotate the trigger assy. about 1/4 - 1/2 inch to the left (clockwise) by whatever means. That will bring your timing back to spec's. If you can do that by assembling the linkage differently or bend the upper arm of the tower shaft outwards away from the block, you should be good to go.

Below is a picture of the linkage between the tower shaft and trigger for an earlier model motor. The plastic piece on the left in the picture attaches to the tower shaft. The plastic piece on the right attaches to the arm on the trigger assy.

NOTE: Ignition timing that is too far advanced is a sure way to damage a piston. This is probably what damaged your piston in the first place.

 

[Markas]

Re: '92 Force 150 O/B problem

Yep, that is very similar to the linkage on my engine. I checked and there is at least 1/4" if not 1/2" or more play/travel left in the trigger coil arm beyond where it currently sits when at WOT before it hits full travel, so maybe by bending or redoing the way the linkage is set up I can get it to move the remaining distance and get it back to where it needs to be.

If I understood the Clymer's, there are trigger magnet(s) under the flywheel (not the stator mags that are visible from the underside when looking up). Any chance these are loose or shifted? If so, how common is this and what are the symptoms if they are loose or whatever? Haven't pulled the flywheel and since it appears to be lined up OK with TDC sort of reluctant to do so.

Thanks,

 

[pnwboat]

Re: '92 Force 150 O/B problem

Highly unlikely that the trigger magnet has come loose or shifted. In addition to being epoxied, it also has a metal ring around the outside of it which helps keep things in place. Below is a later model flywheel that shows them. I don't think you need to take the flywheel off.

 

[Markas]

Re: '92 Force 150 O/B problem

Update***
Pulled boat out after last post in 2010 - not in the water again until now -two seasons later - and a move to NY on the beautiful shores of Lake Ontario - got the boat running and long story short am still seeing the same problem - 18-20? offset on timing when adjustment all the way in. Runs great-had it out this past w/e and got up to WOT and ran for several hours - no issue.

Am ready to bend the tower shaft - before I do - any fresh ideas?

 

[Markas]

Re: '92 Force 150 O/B problem

Ok. Generally boat is running fine. Tried to isolate why the timing is still so far off. Did the following:
1. Removed flywheel. Checked trigger coil and trigger magnet. No apparent damage.
2. Put flywheel back on. Key in place. Checked TDC with piston position and flywheel marking - zero on flywheel corresponds with piston TDC.
3. Unhooked timing block adj screw from trigger arm. Moved trigger arm to furthest position clockwise.
4. Checked static timing with timing light and cylinder #1 -18 degrees BTDC. Expected zero.
5. Marked flywheel for TDC on remaining 4 cylinders. Checked with timing light - same offset - about 18 degrees BTDC as best I can estimate.
6. Put it all back together - same result - 18 degrees at idle and something like 45-48 degrees at WOT static.

So here's my thoughts:
A. Trigger magnet slipped on flywheel. Seemed tight. Picture attached. Gap in trigger magnet offset from keyway by a small amount.
B. Timing light bad? It is a 30 year old inductive light...
C. Don't think its the thunderbolt ignition pack since all 5 cylinders seem the same?
D. Don't think its the trigger coil -same reason?
E. Trigger coil wiring seems ok. Again - miswiring would not introduce an 18 degree timing difference - shouldn't it be much worse if miswired?

So, what would you suggest next?

Thanks,View attachment 161015

 

[Markas]

Re: '92 Force 150 O/B problem

So bought new timing light - same readings as old light so I guess I can rule that out. Ran great all last weekend. Still puzzled.