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When I start my truck up I hear what sounds like knocking for just a split second and then it's quiet. Is there a pressure valve or something in the engine that stops that?

_________________
I've never been wrong! Once I thought I was, but I was mistaken.
Rick
Loranger, La
1980 Stepside LUV (Again)

Not a pressure valve that I know of...usually when you hear a thumping that goes away like that is the beginning of a bering going bad. Main berings usually. Hopefully I'm wrong in this case but it's happened to me before.

_________________
In life there is the "Way things should be" and then "There's the way they are".

2005 Silverado 3/4T Crew Cab
1981 Luv 2WD
1979 Luv 4x4 Currently going through Open Heart and Cosmetic surgery
1995 Roughneck JetBoat
1981 Luv parts trk

There is an anti-drainback valve in your oil filter that's supposed to keep some oil in the engine to prevent dry starts. Oil filters, which generally vary in quality, have variable quality anti-drainback valves. It does take a second (literally sometimes one second) for oil pressure to build up when you start.

Ah yes, the oil filter. I think I'll change it to see if it works. If not, save up for some main bearings!

_________________
I've never been wrong! Once I thought I was, but I was mistaken.
Rick
Loranger, La
1980 Stepside LUV (Again)

its more than likely piston slap.

a condition thats not oil pressure related.

A.j.

_________________
http://www.youtube.com/watch?v=ykgDNjeTa0g

It seems I have to tear the entire engine apart to check everything!!

_________________
I've never been wrong! Once I thought I was, but I was mistaken.
Rick
Loranger, La
1980 Stepside LUV (Again)

If it only makes noise for a split second I wouldn't worry to much about it. Try different weights of oil and different filters. If thinner oil stops or helps your problem it may be your oil pickup. If thinner oil makes it worse like 5w or lower youve probably got problems. I had a rod knocking in a LTD once I tried 60 weight oil in it and it helped. Sold it a few months later for 40 dollars minus battery. Check your oil pressure. I know a guy who put one of those cans of engine cleaner through a 72 Le Mans it was never the same, but it always knocked afterwards from start-up to warm-up to blow-up. Oh yeah, check your compression. I use a napa gold oil filter. When I change my oil oil always runs out when the oil filter is removed no matter how carefull I am.

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1980 4x4

I changed the oil and used Lucas oil additive last week. The engine sounds like it is louder at start up now and don't know if it's my parinoia or not, but, it sounds like I hear the rattling at speed and when I ease off the gas. Making bi-weekly trips to Navarre, Florida must be doing it in. 65 MH for so long at one time with such high RPM's (4-speed manual) can't be healthy for these engines. Now I have to look into cost of rebuilding vs cost of just going out and trying to find another engine that runs and doing an engine & tranny swap, vs getting enough money together to do one. Worst, I might be going to work for the city of Hammond to help maintain their tractors for cutting grass so I need my LUV transportation. If it ain't one thing it's another, eh?

_________________
I've never been wrong! Once I thought I was, but I was mistaken.
Rick
Loranger, La
1980 Stepside LUV (Again)

if its running fine otherwise, not excessivly smoking, low on power, or showing large amounts of flake in the oil - then its probably just fine. Piston slap is just an issue caused by the piston being colder than the bore and thus, slightly loose. it kind or rocks, or "slaps" around and makes that knocking sound. I bet it does it when you rev the motor hard in 1st or 2nd, or when ya let off the gas quickly or make fast downshifts .... just the pistons moving around.... doesnt mean the rings are bad though....

your change in oil weight and additives, are what lead me to believe this.... if it was rods or lifters.... it would have had an impact.

A.j.

_________________
http://www.youtube.com/watch?v=ykgDNjeTa0g

Try to find a cheap oil pressure gage and get an actual oil pressure reading at startup and while it's hot. I drove and '80 chevy pickup for a couple years with a nock at startup. It was main berings showing their age but I had no way to do any better at the time so I drove it. It only did it for about second at startup and then it was done for the day. Maybe you have a bering, maybe piston slap, hard to tell without being there. Good luck

_________________
In life there is the "Way things should be" and then "There's the way they are".

2005 Silverado 3/4T Crew Cab
1981 Luv 2WD
1979 Luv 4x4 Currently going through Open Heart and Cosmetic surgery
1995 Roughneck JetBoat
1981 Luv parts trk

I dug out an old mechanical oil pressure guage today and tomorrow after donating blood, I will hook it up and see what the pressure is at start and running. Yes it does make more noise when I shift gears during high revs. No smoke comming out of the exhaust and it has plenty of power. Well, what power you can expect from these engines that is!

_________________
I've never been wrong! Once I thought I was, but I was mistaken.
Rick
Loranger, La
1980 Stepside LUV (Again)