Hi All,
Our local feed store has a forklift that has never run very well since they purchased it (low power, barely makes it up slight incline). He had a diesel mechanic do a tune up on it (plugs, cap, rotor, points...). He was still having trouble so I offered to rebuild the carb (Zenith). I assumed the other mechanic had at least troubleshooted the motor a little bit, but unfortunately I didn't check the motor out before rebuilding the carb and when I put the carb back on it still ran almost as bad. I did the one spark plug wire off at a time trick and the 3rd cylinder is dead. I pulled the plug and checked the spark and it is fine.
I left a message for the owner to call me because I wanted to tell him he had a dead cylinder. Instead he had another mechanic come to look at it when he couldn't get started one morning (after using it several times since I rebuilt the carb). I happened to come by while he was doing a compression test and the dead cylinder (to my surprise) had the best compression of all 4 cylinders??? I told him about the dead cylinder and he was still trying to blaim the carb, typical.
The fact that it has good compression and spark sorta has me stumped. I didn't do the compression test myself, so maybe that cylinder took longer to come up to pressure, but it seems odd.
Why would a cylinder with good spark and good compression not fire? I've never worked on a flathead and I looked but couldn't find any access to check the valve adjustment, is there one? Could the intake valve not be opening all the way? What could cause this?
He's been using his bobcat to unload the trucks, but it's been bugging me and I'd like to fix it for him if I can. Thanks.
Sven
Showing items 1 - 8 of 8 results.
0.15" is the valve setting intake & exhaust, if you have a gas engine set the plugs at.035" LP 0.25" check compression dry then wet, then do the tune-up. Make sure to clean the points with a clean paper towel, just open the points with a screw driver insert the corner of a paper towel and slide the paper towel through the points to clean. Base setting for the timing is to 1. Disconnect #1 spark plug wire at the plug. 2. Turn the key switch to on 3. Loosen the distributor and rotate until you get a spark. 4. Tighten the distributor and re-install the plug wire 5. Start the engine, adjust the carb air mix and idle. F163, Y112 etc... Engines are very resilient and can take real beating such as lack of maintenance etc... This is all "old school" basic stuff and has worked for me every time.
pull a compression test and come back and show us your results
if compression is good it should be up around 125-150 psi on each cylinder.
Run the test a 2nd time , make sure you put a shot of oil like wd40 or something in the cylinder(s). I always do a dry and wet test to compare just in case of possible ring/valve issues.
If you have compression, spark, air and fuel there is no reason why that cylinder shouldnt fire. Unless there is some kind of obstruction in the intake not allowing fuel to get to that cylinder. And yes, as bigG said, it gives you a better reading on comression testing if you remove all the plugs first, less drag on the engine :o)
Make sure the compression test is done with all of the plugs out, though it is a small chance you could have compression passing from one cylinder to the other. Making sure all of the plugs are out would eliminate that. Back off the adjustment on all of the valve and see if the compression comes up, then do a wet test on all of the cylinders and see if that brings it up. My bet is the motor is old, whipped and tired.
Access panel for valves is behind the intake/exhaust manifold. The manifold has to come off to gain access. If the cyl had good compression then the valve setting isn't a issue. What type of tune up parts did he install- good quality or cheap? I've found champion spark plugs aren't well suited for lifts- A/C or autolite work well.
If you suspect cyl #3 is faulty- switch the spark plugs between cyl's 1 & 3 & try test again. If #3 is still suspect switch plug wires between 1 & 3. If after this #3 is still suspect remove all plugs & take compression on all cyl's while engine is warm & has no spark plugs installed.
If compression check is normal- manually turn engine over while observing valves thru spark plug hole- maybe cam is bad.
It is a gas motor, are the adjustments the same? Same gap for intake and exhaust valves? Lastly where is the side valve cover? That may be a stupid question but I looked on the block on either side of the head and didn't see any access panel.
I think you would be surprised how well these engines run with a simple valve adjustment. Remove the side valve cover and adjust each valve to apporximently.015" and set the spark plug gap to.025" for LP fuel.
Thanks mrfixit,
I did not check to be sure the firing order was right, but if two wires were switched wouldn't there be two dead cylinders? It was definitely cold when he did the compression test so I can try and get it running and do a compression test once it warms up.
How does one adjust the valves on that motor?
Are you sure the plug wires are on right 1-3-4-2 ?
If a valve adjustment is too tight on that cylinder it will fire when cold but as soon as it heats up the valve doesn't make it quite closed and it loses compression and skips. Also when those flat heads blow a head gasket it will leak between two adjacent cylinders. I would get it hot and do a compession check.
Forkliftaction accepts no responsibility for forum content and requires forum participants to adhere to our rules of conduct. Click here for more information.
If you are having trouble using the Discussion Forums, please contact us for help.