Timing marks on MFS4A2 - same side or different than 4/5/6 B/C? (motor won't start)

[Rdubs]

Hi everyone

Anyone know where the timing mark (for TDC) is located on a MFS4A2? I have the factory service manual for the 456 B/C which shows that the mark should be on the starboard side of the motor, lining up with a vertical bump on the motor casing. But I can't find any kind of vertical mark on the casing of my 4A2, the only thing that looks like it might be a timing mark is a pair of marks on the port side casing.

I recently bought a Tohatsu MFS4A2 which wouldn't run. Bought a new carb (6HP version) from Pvnav thinking it was that since they gum up easily but it still won't start. New spark plug and spark looks good. Compression is 45PSI, but I think it has a decompressor. It almost starts but not quite even after hundreds of pulls and new gas. Latest theory is it might be a sheared woodruff key, that would cause the timing to be off. But I did notice the timing mark on the flywheel seemed to line up with these two little notches on the port side of the motor (the side opposite the carb). If the timing marks on the 4A2 are supposed to be on the port side, then maybe the timing is right and I'm back to square one. If the 4A2 timing marks are supposed to be on the same side as the carb, like the B/C, then that's likely the culprit.

Thanks for any replies.

 

[Rdubs]

Hi everyone
Here are two pictures of the motor, where the timing marks might be. The first is the starboard side. Anyone see the timing mark on the casing? That little vertical bump just below the gear selector cam/screw looks like the timing mark on the flywheel, I don't see anything that looks like a timing mark anywhere else.

The second is the port side. I circled in green the little two bumps where the motor seemed to be lining up when the piston was near the top. The timing mark on the flywheel was exactly centered between the two little circles bumps. Anyone know what these little bumps are for? Do they exist on a B/C model and if so do they have any meaning?

Thanks!

 

[pvanv]

Rich,

You are in luck; I just got a 4A2 in the shop, and the timing mark on the flywheel is just like yours. Yes, those bumps are the TDC marks on the block. Actually, there is a third bump, further aft. That's probably the maximum advance mark. If you connect an inductive timing light, you will see the flash as the flywheel mark passes that area.

 

[Rdubs]

Update...I removed the flywheel nut to try and see if the woodruff key had sheared. I couldn't find the key. It looks like the shaft is slightly off center; the top of the picture (which is towards the rear of the motor) there is a very small gap, but there is almost no gap at the bottom of the picture (front of the motor). I'll take the flywheel off next to inspect the key.

 

[km1125]

The timing marks are TDC, 5 degrees before TDC and 25 degrees before TDC.

The timing should be 5 degrees before TDC at idle and move up to 25 degrees before TDC at top speed. However, mine doesn't do that - it just stays at 25 degrees TDC at all speeds. I'm curious what you see when you get the engine running.

Here is a pic from the service manual:

well.. I tried to upload a pic, but I keep getting an error. Will try again

 

[Rdubs]

Hi everyone
Quick update...the reason I couldn't see the woodruff key in that picture I posted was because there was a washer on top of it. Remove the washer and the key was easily visible. Also, one tip to getting the flywheel off is to tighten up the puller pretty snug and then wrap on the flywheel with a rubber mallet - it will pop and release. Works much better than constant pressure, since if it is slightly off in direction it will bind.
It turns out the key wasn't the problem, it was perfect. So back to square one.
Put the flywheel back together and tried to start it some more. One thing I've noticed is that after I pull on the starter a lot, water starts to leak into the cowl and then leak out of the bottom of the cowl underneath where the seam is, mostly on the port side. Since I have to pull on it for the leak to happen I can't see where the water is coming from. Anyone seen this happen or know what this might be? I'm hoping it is relating to the starting problem.

 

[Rdubs]

In case it helps here are some pictures from when I had the powerhead off. I did a wet compression testing using a fair amount of oil, that may be why there looks to be so much oil in the exhaust. If anyone notices anything off, please shout. I'd upload a video of trying to start it along with the water leaking out from under the cowl but don't think the board lets you upload videos.

 

[pvanv]

Yes, you can upload videos. But only you can look and see where the water is coming from. If the power head is not gasketed down properly, it could be coming out there.

 

[Texas Prowler]

Your compression is way too low. It's time for a rebuild. I rebuilt mine and changed the carb and reed valves to 5hp parts and absolutely like how this little engine runs.

 

[pvanv]

Your compression is way too low. It's time for a rebuild. I rebuilt mine and changed the carb and reed valves to 5hp parts and absolutely like how this little engine runs.

This post is two years old. It has been resolved.
This post should be closed.

BTW, those motors have decompression, so no, his compression is fine.