GRD 233 Compression Test

Found a guy with a KBS-5 with 15k miles on odometer. He is not zure but thinks it is original miles and not 115k as it was a farm truck. It has been sitting for a few years so I had him do a compression test. It came back 60-55-60-60-55-70. He said he put.oil in the cylinders a few months back but not before this test. He seems like he is being honest. He is a rat rod guy and says he usually cannot fine people.to take the chassis and engines. I told him he needs to keep my number.

My questions is about the compression test. It seems like the engine should at least run with this compression but what are the chances are that things will loosen up the rings and valves will seat and the compression will come back up?

Thanks,
Mike

it's low but fairly even, meaning no blown pistons or burnt valves,

sitting a long time cylinders can be dry, valves can be slow to close, he could'v had a weak battery,

I did an experiment on cold engine hot engine compression testing of a newly rebuilt motor,

you can search it in this category posts by me, been a few years, you may need to dig a little,

I bought a SD 264 that was supposedly factory rebuilt but been sitting for a few years, when I did a compression test at the site, it was relatively low but even, so I bought it

some years later, I cranked motor over to get oil up into all passages rocker arm, pistons ETC. did another test with a hot battery, got a lot better results,

true reading will be with a bleed down test, not always easy to do while looking at someone else's motor.

factory manual lists compression ratio of a new motor at 6.3

I have a conversion chart somewhere to PSI

Compression ratio x 14.7 will get you the theoretical PSI.

That is about right as i believe 90 is about the right compression. My questions still stands though. What are the chances that the compression will come up on its own without major work if it has been sitting for 20 years?

I would bet on the compression test getting higher..
Take it easy when the motor starts. My cousin and his son started an old Chevy Babbitt bearing engine, then revved it up and destroyed the engine. So, the Chevy continues to sit in a shed. .

I've dealt with a lot of older motors in the past and when you check compression, consistency is important. The readings he gave you are consistent with the 70 reading being the least consistent. One being higher is ok. When the engine runs again, it will try to re-seat the rings to the cylinders and in most cases the readings go up after some run in. If it has high miles and a lot of wear, it will not.
If he put oil in the cylinders a while back, it could have still been sitting in there when he did the test...that would give a higher reading and not be a good test to go by.
Like the saying..we roll the dice and takes our chances. Good luck if you decide to purchase it.

I don't even own a compression tester any more. I have a cyl leakage tester that I use for diagnoses.
With old engines that have sat a long time, I would start and run at idle or low speed until it warms up.
side note, compression readings are supposed to be taken on a warm engine anyway
If the engine has sat long enough to have stuck rings, running them at slow speed to heat the piston may free them. If they are stuck bad enough, when the piston swells from the heat they will score the bore. If stuck bad than you are going to have to tear down the engine anyway.
I had one Gardner 6LXB that I let run for hours, ran slowly around town, but still scored the liner when I took it up to speed under load. The bus was bought sight-unseen in a field, I was sent to Tulsa, Ok to install a clutch and drive it back to Chicago. It made it to the edge of town, and then the rest of the way to Chicago on a wrecker. Sometimes you win and sometimes you loose. Once in Chicago I was able to put one piston and clean up the liner.
Point being a compression test wouldn't have helped. Esp a compression test done on a cold engine.

On my 49 KB-1 Panel I did an experiment just to see about compression tests

This is what I wrote on 1940 and older posts:
so background on the motor, GRD 214 was rebuilt in 1991 and never started, I got it in 2013, took off head, new 30 over pistons fresh honed cylinders, new valves/seats, etc., holes 3 & 4 had some corrosion as there was never a carb installed and moisture got into intake, cylinder walls cleaned good, 3 & 4 intake valves removed & refaced and seats were refaced in the truck, did nothing to other pistons, valves as it was all new, inspected bearings, all crank/rods turned with new bearings,
everything reassembled,

the motor has probably 30 miles and 5-6 hrs. on it, so broke in? probably not, rings seated? probably,

test done with fully charged 6v. and 12. batteries, 12. connected with jumper cables directly to starter, brand new compression tester as my 30 yr old one was giving wacky readings, carb held in wide open position,

6v. cold 1=98, 2=95, 3=88, 4=85, 5=85, 6=98

12v. cold 1=108, 2=102, 3-95, 4=98, 5=99, 6=110

then I ran the truck for about 1/2 an hour, up to operating temp on gauge, block was hot to touch, not super hot,

6v. hot 1=98, 2=90, 3=95, 4=85, 5=90, 6=100

12v. hot 1=113, 2=110, 3=105, 4=100, 5=103, 6=115

conclusions:
to me compression tests can vary greatly, so I wouldn't get hung up on number rather than even across the board,

all old mechanics manuals tell you variances in castings of combustion chamber can affect reading by 10lbs,

12v. tests can make you feel better about your 6v. motor's health by giving you about 10lbs. higher reading

I plan to do another compression test after I drive it a couple hundred miles or so,

Here is the link to the entire post.
http://oldihc.org/phpBB3/viewtopic.php?f=5&t=8885&p=68438&hilit=+compression+test+hot#p68438

Well i took a chance on the truck and got it running today. i put marvel mystery oil in the cylinders a couple of times over 3-4 days. Truck seems to run pretty good although i have not yet retested the compression. I may wait a bit and do that. From the trucks condition and how complete it is i would say it is likely 15k original miles.Truck came from Idaho so only minor surface rust and not much of that.