Question about low compression...
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New User
Joined: Jun 2011
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Question about low compression...
I have a 1978 Ford F-250 with a 400 6.6l motor with 125,000 original miles. It had regular oil changes. I recently removed the oil bath air cleaner and replaced it with a K&N 14"x3" open air element with a vent kit. It also has a new mechanical fuel pump. The timing is retarded by 4 degrees and I have been told that at our elevation (4,500-6,500ft) it should be retarded around 10 degrees.
On it's first trip with the new parts I was pulling a 5,800 lb travel trailer and the rear main seal started leaking after an hour or so at 65 mph. I took it to my mechanic and had him do a compression test to see if it was worth repairing the seal. He said two were low at around 105 psi and the other four were near 125 psi.
Could the timing cause low compression? Is it worth repairing the seal...apparently you have to drop the the transmission? Should I try thicker oil and an oil treatment?
Thanks...
On it's first trip with the new parts I was pulling a 5,800 lb travel trailer and the rear main seal started leaking after an hour or so at 65 mph. I took it to my mechanic and had him do a compression test to see if it was worth repairing the seal. He said two were low at around 105 psi and the other four were near 125 psi.
Could the timing cause low compression? Is it worth repairing the seal...apparently you have to drop the the transmission? Should I try thicker oil and an oil treatment?
Thanks...
Cargo Master
Joined: Oct 2010
Posts: 3,417
Likes: 32
Timing doesn't effect a compression check. It's done with no spark plugs so timing wouldn't com into play.
I don't think you need to drop the tranny to change the rear main either. I've done it on a few 352's only dropping the pan and the rear rod cap. It's enough of a pain in the *** to begin with without taking the tranny out.
At 105 compression it's time to think about a rebuild for that motor.
I don't think you need to drop the tranny to change the rear main either. I've done it on a few 352's only dropping the pan and the rear rod cap. It's enough of a pain in the *** to begin with without taking the tranny out.
At 105 compression it's time to think about a rebuild for that motor.
