MC engine questions

mapaduke@yahoo.com · Post by **mapaduke@yahoo.com** » Sun Feb 21, 2016 5:45 pm

Ok, I've been restoring this MC that had a stuck engine and a cracked block so I picked up a project M from a guy that lost interest and now has gone to the red ones. Anyway when I got the M he had the head rebuilt but not on so now I've gotten the engine back to geather and have it running, something isn't right, the oil pump wasn't timed right so I set the timing the best I could by ear. When I was cranking it over with out the plugs in to build oil pressure for sum reason I put my hand over the muffler while cranking it over there was a slight sucksion on my hand then an an amedate exhaust. Now that it's running it is louder than normal, no power and and it needs a little choke to start it when it's hot.
I'm thinking the camshaft may be off one tooth? What do you guys think?

Post by **Lavoy** » Mon Feb 22, 2016 12:11 am

Suction is not necessarily abnormal. Time it with a light, these are a little hard to time by ear.
Lavoy

gregjo1948 · Post by **gregjo1948** » Mon Feb 22, 2016 6:44 am

I don't understand how electrical timing can change suction thru the exhaust.
Sounds like an exhaust valve is opening too soon. It's opening before the power stroke is finished. If the valve timing is off like that, the exhaust stroke isn't completing before the intake stroke is starting. Maybe with exhaust fumes still in the cylinder, you need to enrich the mixture by choking it to start it. WOW! I may have over thought this or did I under think it?

mapaduke@yahoo.com · Post by **mapaduke@yahoo.com** » Mon Feb 22, 2016 7:34 am

I think I have a couple problems here, in order to get it to run the distributor cap posts are against the block parallel to it and will not run when I set it on the timing marks. If I lean out the mixture it it back fires through the carb. I will pull the valve cover and check valve timing may be do a compression test.

Stan Disbrow · Post by **Stan Disbrow** » Mon Feb 22, 2016 7:53 am

Hi,

Exhaust valves start opening just before the piston reaches BDC on the power stroke. The mean effective pressure has dropped below usefulness by then, but is still enough to potentially overstress the connecting rod as it reaches maximum angle on the crank. So it has been common design practice to crack open the exhaust valve early. This dating back well before the M came along. I have never given it a second thought until just now.

Stan

gregjo1948 · Post by **gregjo1948** » Mon Feb 22, 2016 7:57 am

Can you get the distributor in 180 out? Can you have the plug wires switched? Pull your plugs out, turn engine over holding your finger in #1 hole to feel compression stroke push your finger out and stop rotation at top dead center. Take off the distributor cap and point the rotor towards #1 wire. If you can't turn the distributor far enough, you may have to pull it out and install it correctly. If you have to choke it to get it started, even when warm, I'd think it's already too lean.

gregjo1948 · Post by **gregjo1948** » Mon Feb 22, 2016 8:10 am

Stan Disbrow wrote:Hi,

Exhaust valves start opening just before the piston reaches BDC on the power stroke. The mean effective pressure has dropped below usefulness by then, but is still enough to potentially overstress the connecting rod as it reaches maximum angle on the crank. So it has been common design practice to crack open the exhaust valve early. This dating back well before the M came along. I have never given it a second thought until just now.

Stan

Would the exhaust valve open enough to feel suction on the exhaust pipe? Do they open the intake valve before TDC?

Post by **Lavoy** » Mon Feb 22, 2016 8:53 am

Timing will not affect suction. I have seen multiple engines including rebuilt ones have this "suction". Not that you can't have a problem, I just don't think so. Time the engine with a light, distributor position is irrelevant other than yes you are 180 deg out, but that still has no effect on timing.
No, you can not rotate the dist 180 degrees like we would on a small block Chevy, dist only goes in one way. You need to set the timing with a timing light prior to trying anything else, then you know where you are at.
Lavoy

Stan Disbrow · Post by **Stan Disbrow** » Mon Feb 22, 2016 9:37 am

Hi,

On the suction, keep in mind that you are cranking this, not running it. So, there is no gas pressure from combustion. The piston is running downward with both valves closed. That means an abnormal vacuum in the cylinder, so when the exhaust valve cracks open near BDC on the power stroke - suction thru the exhaust manifold.

On various race engines, where we grind the cam lobes to open even earlier, and we have header pipes, the danged things sound like an ompah band when cranking over.

Stan

Edit: aw, now I got a crazy idea of replacing the manifold with header pipes on my M..... That ought to sound really weird!

What RPM should I tune them for? I never have seen a power curve for a 2-cylinder. I have no idea where peak HP is on these. Something else I have never given a thought to.

Edit 2: and....now thinking on fuel injection.....anyone ever make a four-valve crossflow head for these like Cosworth did for Pinto engines??

Edit 3: how about Formula Deere? You know like an old Formula Ford with a 2-cyl in place of that aforementioned Pinto engine....

Now this is getting Just Plain Silly!

mapaduke@yahoo.com · Post by **mapaduke@yahoo.com** » Mon Feb 22, 2016 9:51 am

Is there a way to set the oil pump timing with out the tool used in the Manual?

mapaduke@yahoo.com · Post by **mapaduke@yahoo.com** » Mon Feb 22, 2016 10:10 am

Ok, after running the engine number one cylinder is at 110 psi
And number two is at 105 psi so if it's a came timing issue I would see numbers a lot lower I would think?

Post by **Lavoy** » Mon Feb 22, 2016 1:32 pm

Cylinder one, TDC compression, distributor slot roughly parallel with the crankshaft, narrow side of the slot outwards is what I remember. This will put the distributor terminal in the correct position, but will have no effect whatsoever on timing.
Lavoy

mapaduke@yahoo.com · Post by **mapaduke@yahoo.com** » Mon Feb 22, 2016 3:21 pm

Ok, feeling a little stupid now. lol
After reading the service manual " completely " it said to bring the RPMs up to 2025 and then set the timing, I was trying to do it at idle.
Seems to run a lot better now.
I did notice while tightening the distributor that it will change the timing if you don't tighten the clamps evenly.

gregjo1948 · Post by **gregjo1948** » Mon Feb 22, 2016 3:29 pm

I didn't think they would rev that high!

Post by **Lavoy** » Mon Feb 22, 2016 4:11 pm

MC should be 1850, rated load 1625. 420 through mid 440 is 2025 high idle, 1850 rated.
Spark mark is 23 degrees advanced. I find it a lot easier to use and advance timing light, much easier to get right on the money.
Lavoy

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