New Cylinder Head

[Firebob]

Hell again,

Many of you have read my threads about my 88 marathon with the 2pg motor. So to recap when I started this project the motor had 60psi of compression so I rebuilt the top end. New cyclinder, piston, rings and crank seals, after the rebuild I only had 90psi compression. After having the motor in and out several times to fix this issue the worst happened and the cylinder head cracked. After no luck in finding a new or used one I had my cyclinder head guy custom machine a new one for me out of a hunk of billet aluminum. He did a fabulos job and the head looks and fits great, but I stilll only have 90 psi compression so now I am very stumped by this. Does anyone have any other suggestions. The cart runs ok but I want it to be perfect because my parents especially my mom drives this at their lake property. So I am starting to wonder if maybe the new cylinder, piston and rings are not good parts. I have adjusted the carb a little and loosened the govenor and this has helped. It runs maybe 10-12 mph, but has a small back fire once in a while and also jerks a little and low speeds. I am going to take off the oil injection and am wondering what a good mixture ratio will be for the fuel and oil. I have enclosed a few pictures of the new cylinder head. So if anyone is having the same issues out there, there is an option and I can give you the name and number of my cylinder head guy. Any and all help or suggestions will be greatly appreciated.

Thank You
Bobby

[Old Ezra]

The jerking and backfiring could mostly be cable-adjustment,IMO. I've been through the same thing with that. As far as the PSI issues. Where did you get the top-end kit??? The head looks great!!!!

[Firebob]

So what cable adjustments do you mean and IMO ? I got the top end kit from a local golf cart shop here in Denver. GTI golf carts and tournaments. The head is a great piece but like I said I am still battling compression issues. What about the oil mix ratio ?

Thank you
Bobby

[pachanga90]

I would look at the rings,and crank-seals.Just because the bore is in good condition,doesn't rule out weak/defective rings,or a glazed cylinder.Also,is the deck of the cylinder square?If its' warped,the head-gasket won't take it up.Mix the oil 128:1 for normal use(1oz/gal.)If you are running it hard,especially ungovenerned,off-road,I always use and recommend 1-1/2oz./gal.I ran my 2pg this way for 4 years,no issues,no smoke.The head looks great!Hope this helps.

[Firebob]

Hey thanks all information is needed and helpful. I would want to believe that the deck is flat and square being new and I would also want to believe that the seals have not failed yet being brand new. I have had the cylinder off several times and the rings looked good and the cylinder still had good cross hatch in it. Thanks for the great info on everything.

Thank you
Bobby

[1989Marathon]

How are you checking the compression?

[daltonruss]

Did you check your reeds? Maybe not sealing.

[Firebob]

I am checking the compression with a brand new screw in compression tester. I also used push in testers and got the same numbers.

How would I check the reed assembly to see if they are sealing ?

Thank You
bobby

[daltonruss]

I usually take the cage out and hold it to some light. Look into the edges ,if you see light its not sealing also make sure the edges arnt broken.

[BrewCityMusic]

this may or may not be relevant, but I recently got some bad parts for a rebuild myself, however that's not where I'm going with this post - where I AM going is that while troubleshooting here on the forum, I found out that if the rings are installed upside down they won't seal correctly (to my eyes they looked the same either way around but evidently that ISN'T the case from what I was told by several helpful forum members) ... Is it possible that you installed the rings incorrectly when you put it together again?

Also, I concur with the cable issue regarding jerky low-speed operation (IMO = "In My Opinion", by the way) - when you set the throttle cable you have to use your ears as well as your eyes, you want the pedal switch to *just* "click" immediately before the throttle arm on the carb starts to open, if the arm is opening at ALL before the pedal switch clicks, you'll be engaging the ignition with the throttle partially open, which will give you jerkiness like crazy if it's severe, not to mention backfiring as when you let off the gas, the throttle will still be open and moving fuel when the ignition is off, therefore causing it to load up and *POP* when you press the pedal again. Are you sure you reinstalled the spring between the throttle arm and cable stop too? Without it, same type of situation.

12mph is factory standard speed for a Marathon, by the way - with the governor disabled you'll get up into that 14mph range or so if you're running perfectly (which on a new engine will NOT happen until you've run at least a tank of gas through it to break it in, seat the rings, etc) - Also on the "Break-in" note, you want to run 40:1 oil premix for the first tankful with a new top end or you risk the rings not seating properly as well as potential failure of the rebuild