Hi,
Just picked up a 1993 F350 with a 460, 165,000 miles. I was told by the PO that cylinder #1 and #5 have low to no compression. I was pulling the plugs to do a compression test and saw that #1 plug was cross threaded and #5 has not been firing, it was covered in oil and there is what smells like gas around the outside of #5 exhaust manifold.

I saw no blow by from the oil fill, or the dip stick tube, some bubbles in the radiator, but they stopped coming as the engine ran. There was no smoke from the tail pipe on start up but lots of white/gray smoke when it warmed up. I'm pretty sure it was smoke and not steam because it did not dissipate.

Because of the striped threads I was not able to do a compression test on #1 and #5 was dead. All others had exactly 80 lbs of pressure as measured by a POS Autozone loan a tool gauge. (The gauge was brand new.) I don't trust the reading. I'll try and borrow a quality gauge from a neighbor.


Is it possible that all others had exactly 80 lbs of pressure?
What should be my next move.


I can just pull the heads and rebuild them. I can then look so see what the cylinders and pistons look like.

With the heads removed can I tap from inside out to try and fix the threads?
I'll also need to replace the oil pan gasket and this can only be done with the engine out, or lifted up to clear the cross member.

Thanks

 

For them all to be at 80 psi I have to ask how many times did you rotate the engine over?
The stripped threads on #5 can be helicoiled, and the cross threaded #1 can be retapped or helicoiled. just make sure to coat the tap in grease heavily so it will catch the shavings

Matt

 

I'd say about 10 times of rotation. #1 is cross threaded. #5 has no compression. I'm not sure if #5 has bad valves, or bad rings. A leak down would show that, but I don't have a tester. Unfortunately they are opposing, or I'd just pull the one side head and rebuild it, but now I have to at least do both the heads.


I was wondering if the 6 others are all exactly the same then its probable the rings are good in all of them. And the low reading was probably due to a crappy gauge???


I'm trying to figure out if I need to pull the engine and rebuild the whole thing, or just the heads.

Thanks

 

You did the compression test with the throttle WOT right? 80 PSI is extremely low.

 

Yes at WOT. I guess what is puzzling me is that ALL were at 80. This is what making me think the gauge is off, plus it was a cheapo gauge.


I know I just need to go ahead and invest in a quality compression and leak down tester, but the combined cost would be about $300. And I still need to get a cherry picker and an engine stand. That's a lot for me considering I paid $1000 for the truck. The truck is worth it to put about $3000 into. Guess I'm being cheap.

 

80 is extremely low, I would probably skip all the BS and head straight for the rebuild or find another motor to drop in it seeing that you are on a tight budget..

matt

 

I agree, 80 is way too low to bother trying to repair anything, but I did get another gauge and will try another test before the rebuild. I’ll repost with new results. I learned from here to never assume the worst.<O</O
<O</O
So far I know for sure that #1 is cross threaded and may just need that repaired and #5 has some issue, rings, or valves, won't know till I do a leak down on #5 after a second compression test.<O</O
Thanks<O</O
<O</O

 

Hi,
I wanted to post an update, just in case someone comes across this and is in the same predicament
I went and got another "loan a tool" from Autozone and this time it showed 4 cylinders to be at 120 and 2 at 122.

Obviously these are not numbers from a new engine, but are great for even wear. So now I still can not tell what the cross threaded #1 and # 5 are doing, but my guess is that they are also fine and just need the head rebuilt.

I will do a leak down on #5 and see if I still need to pull the engine or not, but I'm glad all the compression #s are not 80. It was a brand new gauge, bad out of the box. A head rebuilt maybe all that's needed.

Thanks

 

thanks for circling back and updating, so many of these exploratory threads die off with conclusion.

Odd that both front cylinders are affected. Gotta be something common to them. Both are the easiet to get to pointing to operator error on them both...

thanks and good luck!