Rebuilt Engine wont start

Hello tractor experts! I'll try to keep this as brief but there are a lot of moving parts...

My antique Shramm tractor (a Philadelphia-based compressor manufacturer that briefly branched out into the air compressor / backhoe business) has a huge straight-6 block engine / compressor built on an IH 504 frame. The front 3 cylinders provide power while the back 3 compress air (if wanted). The pistons are 4" diameter and the throw is very long.

One day, about 10 years ago while scooping muck out of a pond, I had to quickly shut if off when - as I eventually discovered - a keeper let go and it swallowed an exhaust valve.

Being stubborn (and not too bright) I've spent a lot of the last 10 years boring down thru the block, removing the bent valve, manufacturing a custom valve-carrying insert and threading it into the block (not the normal procedure I'm sure but the engine is HUGE, parts are impossible to get and I'm working outdoors.) If my repair turns out to be less than perfect I plan to use oil as a coolant to keep water from getting into cylinder #2 - but, as I haven't even added coolant yet, that's not my problem...

I've repaired the slightly bent push-rod and even gone so far as to remove the timing gear cover to make sure nothing has slipped, rebuilt the 24v starter, bought 2 new batteries, rebuilt the carb and even added a pre-oil pump to lube the bearings - and yet, it refuses to start.

The timing light says everything is kosher - I can see the valves opening and closing when they should (and no, it's not 180 off), the mag is providing plenty of spark and (when choked) the exhaust smells of gasoline and yet, it refuses to start.

Any advice will be much appreciated.

Check and see if you actually have any compression. You may have damaged more than just the dropped value when you shut it down fast. Also your repair may not be compression tight.

I recently helped a neighbor kid with a 4-H project. When he went to start the old engine everything looked right, timing, spark, and gas but wouldn't start. Turns out he didn't t have the condenser grounded. Made a huge difference in his spark and then it started right up

Have you checked to see if you have spark at the plugs? Did you replace the plugs?

How fast does it crank? A 24 volt starter should spin the motor very fast. Your 12v batteries need to be connected in series to get 24v. I Once bought a tractor for a very low price at an auction because it would not start. It had a nearly new battery that they also boosted but it would not fire. I noticed the the glow plugs were labeled 24v which clued me that the machine needed 24 volts to spin the starter. I removed the battery from my trailer winch and put it in the tractor in series and the tractor started almost instantly to the consternation of the auction company.

I assume you are using 3 cyl in a row from one end or the other .
If using cyl. 1,2 and 3 firing order would be 1,3,2. If using cyl 4,5 and 6
the the first cyl to fire would be 5,6,then 4. Any chance you have the wiring wrong?
would be easy enough for me to do. Post back when you figure it out.
good luck!

I'll try to reply to all 4(!) suggestions above...

1) I realize cylinder #2 may not have perfect compression as it's the one that chewed up the exhaust valve (and now has the custom threaded insert) but cylinders 1 & 3 should still be good so wouldn't it at least fire on them?

2) I think the spark is adequate - if I advance or retard the timing I occasionally get backfires thru the exhaust or carb but it never fires when it should - at TDC or just before TDC - and acts like it wants to start.

3) The plugs were new a couple of years ago and all 3 show a spark when removed and grounded. The firing order matches the valve action and yes, with 24V to the starter it cranks rather fast.

4) Yes, the firing order is 1,3,2 - verified by the manual and watching the valves open and close.

Thanks to everyone!

what is the compression, and lots of plugs fire in open air but dont fire under compression. I have a old fashion plug cleaner and tester and find 50% of the plugs dont pass. My old motorcycles are particular sensitive to plugs.

When you say timing light you mean small bulb and not a timing light as in running engine. Where is the #1 piston in relation to TDC when firing occurs ?. In other words how are you static timing it?

Reply to the 2(!) new suggestions...

1) I don't have access to an actual compression tester but if I remove any of the 3 plugs the woosh of air thru the hole is quite evident.

2) My electronic Sun Gun timing light works on the mag output and indicates that it's firing about where it should (and I can remove the mag drive and advance or retard without too much difficulty).

Thanks!

Hi
Just wondering if the impulse coupling for the mags messing you around .
I got a fordson E27n long horn here Its 12v but if I spin it on the starter, like starting a modern car or tractor. It turns over to fast for the
impulse to work properly and don't even fire. If I hit it in kinda a short Hit the button then let off, it will fire right up. and same If I feel
energetic with the crank handle. I think the impulse on that one doesn't like a fast cranking speed it kinda overrides the mechanism.
is this why its throwing the timing out to, or is there accumulated wear in the timing gears that after a turn it's out a hair. The fordson major
diesels will do this if the gears are worn.

Have you actually checked compression now as a moving piston will move some air but with a plug in it bypasses , the rings could be stuck.

Are the plug wires shot if . I had a non start sometimes on
that long horn but the wires showed a spark with plugs out, some times it would run nice then ruff, or not start again but pop. I put new copper
plug wires on and it cured it.

After massive cranking and removing plugs are they looking wet, if not the fuels not getting up to the cylinders either. if they are wet you either have fuel or water L.O.L are you sure you don't have water in the gas.
I had this happen with a customers swather once . it ran perfect until he fueled up. The water was in the bottom of his fuel storage tank, then it filled the carb with it.


Just guessing here but It's odd stuff I had problems with in the past. Basically you could have quite a few issues due to the original problem plus the standing for 10 years on top.
Guessings all we can really do without being there.
Regards Robert

Back to basics. The engine needs 3 things to start. If it has those three things, it will start.
1) Compression. Need sufficient compression to compress fuel/air mixture for combustion. Low compression means no start. You need to VERIFY that you have sufficient compression. Guesswork is just that - guesswork.
2) Fuel/air mixture. Fuel and air mixture required for combustion to take place. Ideal mixture is about 14 to 1 air to fuel. Fuel needs to be atomized so that the mixture is fairly uniform.
3) Spark. Properly timed spark. Spark at the wrong time will simply not ignite the mixture as necessary. Weak firing or leaky (electrically) spark plugs will inhibit starting.

So, my suggestion is to start with the basics. Begin with a compression test. Compression testers are not expensive, and are available at most any auto parts store. A set of spark plugs (3 of them?) would cost about $10 to $12?

If you are looking for an answer as specific as which bolt to adjust or what the valve clearances are, I can't help.

Woosh of air is not a good test .A poor mans gauge is to see if compression will blow your thumb off the spark plug hole.

I sell tools I'll sell you a used compression tester for ten bucks.Plus shipping.

Update and reply to the last 3 posts...

1) Thanks for the advice Robert but the impulse part of the mag seems to be working just fine (and why would it cause a problem at low crank RPMs?). I've tried shifting the timing probably a good +/- 20 degrees all to no avail. As for 'wet' plugs after repeated attempts - no they aren't, but read on...

2) I like you 'back to basics' advice jimg, but I don't think fuel and/or spark are the problem - compression on the other hand...

3) ...seems to be an issue. Much to my surprise the only cylinder that pushes my thumb off the spark plug hole with a lot of force was the one I was most worried about - #2 with the custom-made valve holder! While that gives me confidence that my repair to #2 cylinder was a success, it makes me wonder what's up with the other 2 as the engine was running fine before cylinder #2 swallowed that exhaust valve.

I'm going to try adding a tablespoon of oil to cylinders 1 and 3 to see what happens - if there's no obvious compression change I'll assume the exhaust valves on those 2 aren't sealing properly and then have to figure out what, if anything short of tearing the head off, I can do about it.

Dr.sportster: do you have an eBay account if I decide to take you up on your offer?

Thanks to all!

Junk dislodged from a dropped valve can blow back up the manifold and lodge in, or get pinched in the other intakes, or exhaust valves. If the other valves were way out of adjustment (wide) when you put it together, the reason may be junk. if they are close to spec, and similar, that might not be the issue. What may end up happening is a home made head gasket. Soft copper sheet, and a flat deck with no sleeve protrusion will work. Jim

Yes I do eBay but I could just send it to you. If the motor can't blow your thumb off the plug hole then it may not have enough compression to start.Sounds like you are pretty confident the timing is at least close enough to fire it.Post what happens after your wet compression test.

Update / reply to the last 2...

1) I cut power very quickly when the valve got swallowed and when I finally got it out, it was in good condition except for being bent and therefore unusable (I don't recall any carbon 'junk' at all). The 2" dia. replacement valve and guide are surprisingly identical to the originals. A rare example where OEM parts were available from someone - possibly a former Shramm dealer - who had a little stock.

2) Adding a Tablespoon (maybe 2) of motor oil to cylinders 1 & 3 took them from 'hardly any' to 'enough to force my thumb off the hole' compression. I find this odd because the cylinder that has the custom valve insert has good compression w/o benefit of additional oil but I plan to add some anyway as the cylinder walls probably haven't seen a drop since 2005.

Dr.sportster: that sounds good but how do I provide a shipping address (and make payment) w/o posting it here? Wouldn't eBay & PayPal be easier?

Im trying to open up my email now. I contacted the admin.

Rings can stick when sitting for long periods of time. It may just be a case of stuck rings on the other two cylinders. You may find that adding the oil and letting it sit for a day or two will unstick them. Add some marvel mystery oil to those two cylinders and give it a couple days.

Or add a some automatic transmission oil to soak the rings on cylinder one and three.