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Running on 3 of 4

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MGTF1250Dave

MGTF1250Dave

Jedi Knight
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Aloha All,

It seems I've been driving around for the last few weeks with no compression on one of four cylinders. Lack of power was not that noticable because I drive on mostly flat roads. I first thought the problem was ignition and replace most of the parts. Finally I did a compression check and found the problem. I've ordered the parts to pull the head and replace the valves in #4 cylinder. Have I caused any other possible damage to the engine while driving it like this?

Safety Fast,
Dave
 
This sounds familiar, I'm doing number 3 on my TF 1250 now. You may want to consider having the head rebuilt to go to hardened seats so you can use unleaded gas and going to more wear resistant valve guides.
 
As long as you have the head off, you could consider doing all of the valves. If one has gone, the others are not likely to be far behind.

Whether any other damage was done depends on how long it ran in that condition. A possible problem is that washing from unburned fuel removing the oil film has caused excessive ring & or cylinder wear in the #4 cylinder. At least change the oil.

If reliability is not important, just "fix" the one cylinder & on your way. At least you can't get stuck very far from home.
smile.gif

D
 
Assume you have checked the valve clearance and it is closing fully? Have you run some "SeaFoam" through? Had a cylinder decline seriously in compression and turned out to be some carbon (apparently) in the valve seat that a dose of "SeaFoam" (Checker Auto, etc.) blew out and put compression back to normal for that cylinder. Pulling head is major undertaking but if needed, it's needed.
 
A hint --
When doing a compression check, if you find a low cylinder, set the engine with the valves closed on that cylinder & smack the tip of the valve stems with a soft hammer. Several taps, hard enough to open the valve against it's spring. If there is a bit of carbon between a valve & its seat, as John suggests, this will often dislodge or mash the carbon so that the valve fully seats.
D
 
Aloha,

Thanks FWK, Dave & John for the advice, still 0 compression on # 4. I cranked it over to # 4 at TDC, removed the spark plug and shot compressed air in through the hole. A loud hiss was heard at the exhaust pipe. The exhaust valve seems to be the culprit. I'll know for sure when I pull the head.

The head was proffessionaly rebuilt about 2-3 years ago with new hardened valve seats, stellite faced exhaust valves, valve guides, etc. Hopefully the problem is limited to only # 4.

On a positive note, I have parts to change the rearend ratio to reduce engine revs at highway speed. With the current reduced power, the car had plenty of power except for steep hills or long inclines. I'm no longer concerned that this change will have a big change to acceleration in most situations.

Safety Fast,
Dave
 
Actually, you should gain a lot of power. In addition to the 25% loss of power there are pumping losses on the dead cylinder which could lose another 10 -15%. With a 35 - 40% gain There should be no problem pulling the higher gear.
D
 
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