VCCA Home Forums TECHNICAL - GENERAL Mechanical - Engine, Trans, etc compression test

Hi any one know the compression test pressure is of a 171 chev 4 ,? just had 30thou rebore, done 40miles ago and has a bit of blowby,any one seen that with freshly rebored motor? Thanks

Last winter I was doing a lot of maintenance on my 28 and when I checked compression I had 55 psi on all four cylinders. Not sure if it has Ben rebuild, when I checked the rods they still had a number of shims.

You need to put some more miles on the engine and allow the rings to seat. Then you can be concerned if you still have excessive blowby.

It will take 500 to 1000 miles for the rings to bed in much at all and 2000 mile to fully bed in. I would expect reducing blow by up to the about 2000 mile.
Tony

Ok i have the problem that the crankshaft pressure is causing the lifters to leak resonably bad , have replaced origonal lifters with ones in better condition but still leak the same, anyway ill clock up a few miles and see how it gos,would be good to know if anyone else has had the same oil leak after a rebore with a chev 4

Is the crankcase vented properly? If not, the extra pressure in the crankcase might push extra oil up around the lifters.

Dean

Yes breather pipe is open ,dont have the origonal vented cap. I will put some miles on it and see what happens.

If the cap is not vented, I believe the crankcase will be over pressurized.

I have a couple of oil tube caps in my stash that have holes. If you're interested, I'll sell you one for $5 plus shipping. One has two holes and the other has seven holes (see the attached photo).

Lemme know, Dean

I dont have a cap on the breather pipe at all , it is open.ill put a few miles on the motor then wory about it then i think.the pistons we used were the modern type with the very thin rings which are supposed to have less outward tension than the old thick rings.the idear is a smaller contact area (rings to bore) needs less outward tension , less friction ,fuef efficency. Well thats supposed to be the idear??? All rings were cheaked for gap in cyls before fitting ,and up the right way, and joins were spaced in the correct spots on the pistons so that shouldnt be a issue. I think i will just run it and see how it gos, just have to keep washing the leaking oil off.

With low tension rings it will take a while to wear off enough of the cross hatch pattern on the cylinder walls to seat the rings. Once the rings and cylinder walls are comfy with each other the blow by should be reduced. Do you get much flow from the pipe with the cap off? I would think that an open pipe would relieve the pressure to push oil past the lifters. What break-in oil are you using 10-W30?

There is a pulse at the breather tube and a small amount of oil ,if you have ever removed the breather pipe and looked into the crankcase while the motor is running you can understand why there might be a little oil spitting out with even a small amount of blowby.im using plain old supermarket 20w50 no frills oil to run it in, but im changing to "penrite running in oil"10w40 specially made for running in ,i think 10w30 might blow straight out around the lifters ?

If you use an oil that is thick (50W) for example it may not vaporize and splash up on the bottom of the pistons. However, you don't want too light either. I suggest a 10W30 for the next oil change.

The lubrication of mid-30s and earlier Chevrolet engines is similar to two stroke engines. Most of the lubrication is from and oil mist produced when the dipper passes through oil in the troughs. 20W-50 is too viscous for break in and except for very high ambient temperatures >100 deg F. You want plenty of tiny oil droplets hitting the cylinder walls to lubricate the rings as well as the wrist pins. Higher viscosity oils produce larger droplets that don't do the job. I understand that you don't like the oil oozing past the lifters but you won't like premature wear of a wrist pin even more. Or a sticking piston ring either.

Yep im going to the run in oil 10w40.penrite recomend after running in ,there 20w60 shelsley, they say it replaces the 30 grade of the 1920, google ,penrite shelsley lite 20w60.

Their 20w60 shel........

A 20w60 is way too thick. See Chippers post up above. The wear will be excessive and even reduce power trying to move oil that thick. Break-in oil choice is usually as thin as possible since clearances are so tight.
You could look at a full synthetic 10w30 after break-in if you have concerns with high environmental operating temps but anything thicker with not provide the proper misting effect.

Penrite has some great specialty products for older engines, but these thick multi-grades are not the best spec for this particular oiling system.

This 20w60 oil is the oil they recomend for chev4s splash lube motors.if you look at the label of their oil bottle in their adds,you will see 20w 60 and just below it ,that it can be used were 30w was used. Im going to send them a email and ask them about the misting of their oils.

My gut feeling, even though I am a Penrite fan, is that SAE 30 is too heavy for anything that does not have pressure fed rods, never mind 20W60.

There are people in this thread (not me) who have very extensive experience with the Chevrolet Four. IMHO listen to them.

I will not put 20w60 into anything that isnt worn out let alone a fresh rebuild,would even be tempted to use 5w30 for the first 200 mile then switch to 10w30.
Tony

Yep ill go to 10w 30 i think , this is from the back of penrite bottle of shelsley, light 20w60,medium 25w70 and heavy 50w70,replacing sae 20 or 30,40 and 50 ?

The second number in the multigrade is the most significant one for a "nice weather" vehicle. In the case of 10w30, the oil when hot (212F) thins down to +/- 30 weight which is about right for these older engines on a summer day.

The first number in a multigrade is really only significant in cold weather. Let's say it's -20 out (C or F). When you start your engine, the 10w30 has the cold CHARACTERISTIC of a 10 weight. It's still thicker than the 30 weight is at the hot temperature but as it warms up it thins down to 30. That's why 5w30 and 0w30 exist. In simplistic terms they both thin down to normal 30 weight at full operating temperature but when cold they are designed to flow more easily than a COLD 30 weight oil. Once the engine is hot, it cannot tell whether it has 0w30, 5w30 or 10w30 as they are all a 30 weight when hot. The first number only affects the starting thickness and you want thin oil to circulate quickly, especially in cold weather.

Some of the oils you list have 2nd numbers of 60 and 70. These are really, really thick oils. Even the first numbers are high. A 50w70 in an engine would have difficulty cranking over and could cause wear as it's too thick to pump well on startup and will likely never splash or mist even when hot.

I suspect these thick oils are intended for very tired, loose, full pressure oiled engines, almost as a last ditch effort to keep the engine running...

Back in them thar days, we would add a qt of kerosene to the oil and feed some Bon Ami down the carb in order to set/seat rings. I DON'T recommend this procedure, but you get the idea.

For some excellent comments on building the Chevrolet 4-cylinder 171 cu engine, go to "School is in Session" under Tech Talk on this Forum.

Also look up Dean "Rustoholic" Meltz dissertation on the same subject for some good solid advice.

The numbers i have put on here are from penrite you can see for you self simply google "shelsley oil"and yes i will take a look at those.

Excellent oil grade summary Canadiantim. Couldn't have done any better myself.

JH,

Might try pulling a load behind it at a good speed for about 50 miles or so. It will help seat the rings to the cylinders.

Here is what to do. Get a small trailer and load about six to eight good sized sheep in it. You're looking for about six to a thousand pounds or three to five hundred kilos. (Remember that your favorite ewe may get in the mix. Unload her.)

Drive up and down some inclines. A good pull, without overheating, is what you're looking for. The sheep will appreciate the ride and show it by smiling at you when you unload them back at the pasture.

Good luck. I hope this helps. No down side to this. Just think, when it's time for market or shearing, they will come a-running as soon as they hear that thing clatter near the pasture. Music to their ears. Is too!

Best,

Charlie

Take your favorite ewe on a ride all by herself. Right there in the cabin with you. And, never, never, ever teach her to talk.