Hondo78
Junior Member
- Joined
- Jun 11, 2019
- Posts
- 16
- Reaction score
- 7
- Location
- 94531
- First Name
- Roger
- Truck Year
- 1989
- Truck Model
- 3500 crew cab dually
- Engine Size
- 454
1986 c10 factory 305 engine 52,000 original miles. I bought the truck from PO he had it running but said it had been sitting in a barn for 7 years. The engine runs good but the oil usage is bad like a quart every 350 to 400 miles. Has no leaks no smoking on initial start up but you let it sit idling for 2 to 3 minutes and there's excessive smoke from the drivers side exhaust. Spark plugs on that side are oily with cylinder 5 and 7 being the worst. Compression on that side range from 145 to 155. What do you guys think? Broken rings? No smoke on start up kind of rules out valve seals?
This will not be well received but here goes,
1. Drive down your street in first gear to 25-30 mph and let off the throttle if it smokes you likely have valve seal issues. If you accelerate hard and it smokes you have ring issues.
2. I Bought a C10 new in 1985 with a 305 automatic, after 10,000 miles I returned to Parker Robb Chevrolet and asked for an engine evaluation as the truck would burn a quart of oil between oil changes, (1500-1600 miles). The truck was returned with a GM report, stating burning a quart by 1500 miles is within spec.
3. Valve seals are an easy weekend fix, rings can be reseated by putting a table spoon of baking soda into the intake and working the engine driving up a grade at a brisk pace. (Not recommended but common practice in 1985)
The 305 is not a worth while engine to rebuild unless you need a numbers matching engine; they do however wake up with matching pistons sizes and a balance, with a mild cam and better OEM 305 small chamber heads.
What I did in 1985?; I bought a balanced 350 with, small chamber small valve iron heads and installed a mild cam. Oil consumption issue was no longer an issue, the peddle feel improved and fuel economy picked up by 1.5 mpg highway.
Noteworthy: My 305, when disassembled had three different sized pistons installed directly from Chevrolet, so balance was not a concern at Chevrolet in 1985. The engine was produced in MX as were most of the common low performance small block line up after 1970. That's why we bought BMW 320I's for our spouses to drive, better build quality. GM was fat and happy.