ColoradoHills

I Have a bad cylinder due to a broken spark plug. It now has low compression in that one cylinder and the engine it running poor. What to do now? is my only option to replace the engine? or is there another way.

98fourdoor

Is the spark plug just broken off in the cylinder head?

ColoradoHills

It broke off and bounced around inside for a bit yes

thundaluvin

That happened on a chevy I once had. All I did was replace that piston and it ran fine. Only downside is if you scored the cylinder wall. then you need to bore it out or sleeve it

red_dog007

Might as well do the poor mans 4.5L stroker.

What spark plug did you use and how old was it?

98fourdoor

If you got the old plug out have you just tried putting a new one in to see how it does?

ColoradoHills

Bosch Platinum brand new.

ColoradoHills

I have driven it since with new plugs in it and it is now just a rough running motor. Trying to decide what to do.. I wouldnt mind spending some serious money to get this motor fixed i just cant seem to fork out the $3000 for a rebuilt one to be put in.

KD3NE

I'm in a similar situation.

My plan is to purchase a motor pulled out of a wrecked vehicle and either install it as-is, or rebuild it then install.

If I install it as-is I will be rebuilding the original motor over time so I do not have to put out all the money at once.

The pull-out motor is costing me $200 - owner says " no leaks, no knocks, oil pressure good "

freegdr

first decision would be to repair, rebuild ,buy rebuilt,or used,if it was me seeing either way you gonna pull the motor id pulll the head maybe it just did a valve in then its just a valve job and put the head back on

freegdr

make sure you hear it run b4 you nut it and let it get to operating tem before you buy a couple guys on here got bad motors

KD3NE

Yeah, I thought about that.

Had to pass on two motors this week because the could not be run as the owners were parting out vehicles and sold pieces off the motor.

If this guy can't get it running I might get it anyway and plan on doing the rebuild to it.

It's a gamble either way, unless I rebuild before putting it in mine.

I did a motor swap for a friend, we drove 60 miles to get the motor. They guy started it up, sounded fine and let us drive it around his farm. Got it home, did the swap and my friend was happy for three weeks then it threw a rod. It sounded fine when we picked it up. Ended up pulling that one and doing a rebuild anyway.

My other option is to see if I can buy a rebuild 'short block', but that is not what I want to do at this point.

The XJ with the noise is my toy, so if it dies it can sit until I get to it ...but what fun would that be!

I figure it this guys motor cannot be started, it should be able to be cranked and at the least we could do a compression test if nothing else.



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freegdr

if he cant make it run offer less

98fourdoor

Compression test will tell alot but not everything. Still could have low oil pressure or spun bearings. But for 200 you could afford to pull the pan and check the main and rod bearings and possibly throw a new timing chain in there.

Leethecableguy

Does the motor you have run? If so can you look down in the cylinder after you run it and see if there is oil in there. If there is oil down in there you probably scored the cylinder wall. If there is no oil in there you can put a compression tester on the cylinder w/o the gauge on it put your thumb over the end and have a buddy turn the engine over slowly by hand. When you feel pressure on your thumb stop turning the engine, if the pressure doesn't hold then you may just have messed up a valve and all that needs to be done is replace that valve or cylinder head. If you have the time I would pull the cylinder head off and see what you have going on in there. You said there was a tap which makes me think you just have a bent valve. 4.0l motors have enough clearance a bent valve wont usually mess up the piston.