Head swap help needed

B

brianproctorla

Well-known member
I am in need of some help.
I am wrapping up a 250-2v swap for a 65 mustang i6 with 200 engine. I have it buttoned up, it turns over and has spark. I checked the compression in the first two plugs and got 90 pounds. I think my rods (from the 200) are too short. I used the pedestal from the 250-2v. How can I troubleshoot this?
Thanks
Brian
 
what was the compression in the other four cylinders? did you CC the head?
 
It's not the rods. Do you know your compression from before the swap? It's either rings or valves. I don't think the head's chamber volume should make that much of a difference. Do you have all the plugs out, throttle wide open and giving it several strokes before reading? You can do a wet test with oil in the squirted in the cylinder to determine if it's the rings or a leak down test to determine if it's the rings or the valves that aren't sealing. You can often hear where the problem is when doing a crude leak down test with compressed air.
 
That might be the issue. I didn't pull all of the rods and jumped the solenoid to crank the engine. I can pull all plugs, open the throttle and try again.

I suspected the rods as when I went to tighten the adjustable rockers (turning the engine and then rolling the rod), I pretty much bottomed out the nut at the point where resistance was felt.

I will take better readings tomorrow using the method you described.

Would a leak down test also check for ring problems?

The car doesn't seem to want to pull gas into the intake. I can see that the accelerator pump is working and have blown starter fluid down the intake, but I get very little result.

The spark seems ok and the engine does crank.

Thanks for the help
 
Sorry, meant to say I didn't pull all of the plugs. I never had the head cc'd, but a machines shop did give it a good cleaning and check
 
Pulling all the plugs makes it easier to turn the motor over when testing one cylinder at a time, and opening the throttle ensures air can freely flow in. It's quicker and won't wear the battery down. Just don't smoke while you are doing it if the fuel is hooked up and disconnect the coil wire. It helps to have a friend, one person cranks while the other watches the guage, or a momentary switch wired to the solenoid. You will get a compression bump for each stroke. You should stroke the engine until the compression tops out. But also be aware of how many strokes it's taking to get there. It should only take a 5 or 6 strokes. If a cylinder is getting up to good compression but taking many many strokes, there is a problem there. In the case of poor compression on one or more cylinders you can poor some 30 wt oil in the spark plug hole, turn over the motor a couple of times and test it again. If that cylinder comes up when you test it's got bad rings. Leak down involves pressurizing the cylinder through the plug hole with air when the valves are closed and then deciphering where the leak is, rings or valves.
 
You said you used the pedestal(s?) from the 250 2v, I assume they are the same height, but only you would know that by visually comparing them.
 
Good points all around.
I will measure the pedestals as well.

It was getting up to 90 in about 3-4 strokes, and topping out there .

If the compression was at around 90, wouldn't it still run, but have bad performance?
I am not getting any sustained detonation.

Car ran fine with the old log head, prior to the build.
 
brianproctorla":tuu87r6i said:
I am in need of some help.
I have it buttoned up, it turns over and has spark. I checked the compression in the first two plugs and got 90 pounds. I think my rods (from the 200) are too short. I used the pedestal from the 250-2v. How can I troubleshoot this?

I suspected the rods as when I went to tighten the adjustable rockers (turning the engine and then rolling the rod), I pretty much bottomed out the nut at the point where resistance was felt.
Click to expand...

:unsure: you might be on to something if you happened to have cranked some of the adjusters down to far bottoming out the lifter then it may be holding a valve open. Loosen up the adjusters and try resetting them again sometimes you might not feel the slight drag on the push rod as your spinning it before you have gone to far. If you still end up with the adjusters bottomed out you might need to get an adjustable push rod to check the length you need (longer) for your combo. Yes if you have 90 PSI in each cylinder or within 10% on all it should run did you test all the cylinders? Good luck :nod:
 
That is a good idea concerning the adjustable push rod for measurement purposes.

Maybe I should revisit my adjustment method entirely.

Can someone give a quick guide as to when the rod should be adjusted? I think I hand cranked the engine until the rod was at the lowest position. Spun the rod as I tightened the rocker and went a fractional turn after I felt resistance.
 
when doing the preliminary adjustment of the valves, you want the lifters on the base circle of the cam, run each cylinder to tdc on the compression stroke to achieve this. when adjusting the valves, you want to adjust until there is no vertical movement. if you rely on spinning the pushrod, it is too easy to adjust the valves too tight. you just want to take up the slack in the valve train, and then preload the lifter slightly.
 
brianproctorla":2uf0o3un said:
That is a good idea concerning the adjustable push rod for measurement purposes.

Maybe I should revisit my adjustment method entirely.

Can someone give a quick guide as to when the rod should be adjusted? I think I hand cranked the engine until the rod was at the lowest position. Spun the rod as I tightened the rocker and went a fractional turn after I felt resistance.
Click to expand...
Have you seen this article from classic inlines on adjusting valves?

http://classicinlines.com/ValveAdj.asp
 
When the piston is in the top dead center position, is the rod at its highest or lowest point?
Just to make sure I am starting off on the right foot, is tdc , for cylinder 1, around the zero setting of the timing mark?
 
X2 it's one of the best and fastest ways if you follow the simple Rocker adjusting procedure that "Gene Flore" posted above (in the C.I. Tech link). To answer your question Yes some of the push rods are at there lowest point when crank is on 0 degrees or TDC and lifter is on the heel of the cam. 0n # 1 both the Intake and Exhaust Rockers are as well as 4 others. If your more comfortable doing each cylinder separate at TDC as "rohm" stated that also works good. Good luck :nod:
 
Head gasket?
If it still had the original when pulled then the head needs to be shaved to compensate for the increased thickness of the new replacement gasket.
 
Ok then you will need to turn the crank 120 degrees then 240, 360 etc. after doing #1 or you just pull the distributor cap and watch when the rotor gets to the firing position on the cap for each of the other cylinders. Good luck :nod:
 
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