Need help with 361 M75

Having problems with a military 361 V8. Engine was rebuilt about 10 years ago and was never started and the previous owner put a little marvel mystery oil in the cylinders every few months and turned it over. The carb currently does not have gas going to it. only trying to get it to fire with starting fuild to make sure it's good to go before I put gas to the carb. Original carb is switched out to holley 4 barrel 650 cfm with edelbrock 383 performer intake manifold. My issue is that I can't get it to start, even using starter fluid. No sputter, no hits, just nothing.

Here is what I've done:

1. Confirmed timing and made sure that is was not 180 degrees out.
Used bore-scope to watch valves open and close by bumping the engine, once intake valve closed, let it come to TDC then aligned the timing mark with the 10 mark. Turned engine over and check with timing light and adjusted distributer.

2. Checked and set both points. Cleaned points and then set them to I believe 17 or 18 gap (what ever the manual called for). (why are their two sets of points? Just curious if two are actually needed and why, can I remove one?)

3. Put new plugs and gapped them to .030.

4. Checked compression and each ranges from 120-130 after 4-5 seconds of turning over.

5. Checked to make sure each plug was firing (spark).

Using remote starter switch (with ignition and master switch turned on) tried to start engine and nothing.

Sprayed a little fuild into the air horn then using remote starter switch started trying to crank. There was a little puff every 3 to 4 seconds then a big bang in the passenger side mufflers about 7 or so seconds into the process, this happened a few times from the starter fluid fumes building up in the exhaust and then being ignited. That is about the only life I can get from the engine.

WHAT THE F*** can be the problem with this engine? Weak coil? internal timing off (if that was the case then I think that there would be serious compression issues plus #1 seems timed right. I'm about at my wit's end and almost ready to yank the engine even though it's a huge huge pain in the ass, esp since I'd have to get a gantry crane to do so. PLEASE HELP!

Thanks
Jason

You need to fill the carb with gas and prime the intake with a little gas. Ether alone won't do it.

I vaguely remember the M75 is reverse rotation to a typical V8. Did the rebuilder use an aftermarket cam that maybe is all wrong? Is the starter aftermarket and turning the engine the wrong way? Do this: pull all 8 plugs, reconnect to the wires, and place on the intake. Grab the remote start button with one hand, and place your thumb over the plug hole, and crank. Does your thumb get blown off each hole at the exact time that a spark occurs for that plug?

The items internals are all original military as I have the rebuild sheet for it and the cam was good so not replaced. The rest of the items were good and within spec as well. Only thing replaced were some bearings, seals etc. The starter is correct and orignal. I checked the rotation on the distributer and it's correct as well (bumped the engine to see if it rotated the same way the picture and firing order shows). I'm thinking that I might just need to put some gas to the carb and then try it again. Will do in the morning before I go to work and after the neighbors wake up. hope it fires up as I'm about to pull some hair out

Austringer said:

I'm about to pull some hair out

Click to expand...

Been there many times. The trick with the thumb over the hole was shown to me by a Mexican immigrant after I had wasted much of a day trying to get a 351W to run after being rebuilt. Good luck and let us know how it turns out.

I learned the thumb trick from working on 4 cylinder jeep engines and learned a new trick today with the 361.. I took my compression meter (the gauge has a quick disconnect from the hose) and screwed that into the plug hole and hold my thumb over the end of it, that way, I can pay more attention to other things than trying to contort my hand to get my thumb over the hole, I just bring the "hole" to me.

I will be glad to post the results from tomorrow morning as one of two things will happen. 1) engine will fire up and run or 2) I will have no hair and more than likely no usable engine as I pour the remaining gas on it, and toss a match as I walk away.

Still no fire but a few more single puffs and every now and then a backfire. Checked timing, good. Set dwell on each set of point and total dwell for both points is 39 spec is 35-40. Reset timing after adjusting dwell. Changed out coil, changed out condenser. Still not wanting to run. put a little gas down the carb to prime the intake, still nothing. About to pull my hair out of my head and almost ready to yank the engine. going to go back over everything one more time.

Have you checked the coil? Do you think it might be on the weak side? What part of Atlanta are you in?

Checked that too, nice and hot blue spark. plus, pulled a coil from a vehicle I had running to see if that would make a difference, nope. just does not want to fire up. About to pull the radiator and ponder pulling the engine (which is a huge pain in the ass)

NDT is correct in that you need more fuel, ether alone will not do it. However, the M75 does not run in reverse. What he is probably recalling is the cam runs reverse to the civy models because it is gear-driven, not chain driven.

Define "a little gas". When I attempt to get a dormant engine running, I will dump about 1/2 pint down the carb. When it busts off, it will run for about 10 seconds with that much.

She lives, only on ether at the moment as no gas is getting to the engine via the carb. It has a Holley Truck Avenger (670 cfm) that was completely lacqured up on the inside. Pulled it apart tonight and it's now soaking in a carb cleaning bath for the next 24 hours. It was just nasty inside and all sticky. Once I get the carb rebuilt, should run very nice.

BTW, the issue was the timing, it was way delayed hence the misfire and huge backfires. I had marked both timing marks the same way and when I was timing, I was using the wrong timing line. When I realized there was a second spot to time engine from driver's side, I realigned TDC using the borescope, then marked the passanger side line in white and the driver's side timing line in red, timed it again and boom! She came to life, and purred on ether.

Thanks for all the advice. Saved me about 20 dollars in gas, which I was going to pour on the engine, throw a match and walk away.

Jason

To elaborate on BT3.3's comment. The cam is gear drive w/o idlers so it turns backwards. It has a mirror grind and can be found on ebay for about 70$.

Suggest you carefully check bottom of filter can (stock cartridge style). It can become a sludge trap of sorts. There is also a filter bypass in the bolt. If sludged up make sure that is clean.

Other oddities. Ex valves are 7/16" sodium cooled with rotators. Stock carb is 50's vintage Holley teapot style and has a governor run off end of camshaft. It has an unusual small base, similar to the early (first year only) WC4B (William Carter 4 barrel). I think only a few cars used it (55 Vette?). Carters first 4bbl BTW. I think it had an iron body. So, not may choices for a better 4bbl on a stock manifold. Adapter might be an option but height is a real problem as radiator directly above. Performer 383 is one inch taller than stock. TM says the stock intake manifold bolts torque spec something like 5 or 6 ft-lbs.

The M75's used in the M113 had a different crankshaft (output flange has different offset, length and 8 bolts symmetrical instead of V's asymmetrical 6). One of the members here said the cam lobes were different too, config'd for the auto trans. Flywheel and ring gear is 1"smaller OD and much thicker. Not sure, but starter drive gear would need to be bigger OD (radius 1/2" bigger).

Correction- The -24 TM has intake manifold bolt torque at 45-55 ft*lbs, not the 5-6 ft*lbs figure above. The lower figure is for the old BB Hemi. Sorry.