Excessive Blowby in a Refreshed Engine

[Bill Hudson]

Folks,

Just finished helping a friend replace a refreshed engine in his Cub and it is blowing a lot of oil out the breather/filler tube. So the hunt for the problem begins, here are the facts:
Engine was:

hottanked
Miced and found to be within spec for standard rings and bearings
Cylinders honed
New valve guides installed
Valves and seats ground and lapped in
Head was surfaced
Polished crank

My friend and another fellow installed the rings and bearings and assembled the engine
My friend and I installed the engine

installed and timed governor and magneto, nice 1/4 inch blue spark
Adjusted the valves .015 cold
New plugs
Thought compression was low 45 to 60 pounds dry, 45 to 67 pounds wet

Finally got the puppy to run using a 12 volt battery that spun the engine fast enough to start it. Now the low compression is explained by blowby out the breather/filler pipe, lots of blowby. My thoughts are:

cylinders not honed properly
Rings not installed properly
Ring end gaps too large
Ring end gaps not staggered enough

The machine shop has a sterling reputation and is the one I use/recommend, so I'm comfortable with his work, however, we all make mistakes. The engine has not been opened up yet.

My friend needs the help to get this puppy running with greatly reduced blowby. Any light you can shed on this will be much appreciated.

Thanks.

Bill

[gitractorman]

I'm betting the rings are not installed correctly. Given all of the information and what looks to be a thorough job, I'd bet it was something simple like the rings not installed in the right order, or the all the end gaps lined up. Low compression and blow-by = ring problem. Luckily, you can drop the oil pan and pull the head, and take care of it without removing the whole engine.

[Eugene]

Thought compression was low 45 to 60 pounds dry, 45 to 67 pounds wet.

If this is the compression test results after the engine rebuild, valves are also suspect.

I would plastigage the rod and main bearings when I did the in tractor tear down.

[Smokeycub]

Well Bill, Sorry to hear that. I'm guessing you already know what's going on.

Low compression and blow-by = ring problem.

I agree. It could be any/or a combination of the hone work, which type of rings, fitting of rings, and alignment, but on any re-ring I've done (Cub or otherwise) there's never been an issue with blow-by. I have had some oil consumption until the rings seated and that cleared up pretty quickly.

[ricky racer]

It's pretty much has to be rings or valves. Easiest to check is valve adjustment. It's hard to believe that a 50 year old engine is still within spec. with a standard bore. If the cylinder bore was at the upper limit then honed out to clean up the bores its more than likely well out of spec. now. What did the end gaps measure before installation? If the valves are properly adjusted, a bore job, new pistons & rings will make it like new.

[Boss Hog]

Bill I am sure that a new set of oversized rings filed to fit will solve the problem. I expect you will find an assy error , broken rings, etc
Boss

[SouthernOutlaw]

I agree with every body that it is probably a ring problem. My first question with the rebuild is did anyone use a ridge cutter before honing the cylinders. I have made that mistake one time. Never again. Recheck the cylinder bore for out of round. It doesn't take much to keep rings from sealing. Also make sure the rings were not installed up side down. Again ask me how I know. Should be easy to find the problem, but will take a little checking. Ring gap. Buy next largest size file to minimum gap. New std rings may be at max gap. With every thing torn down rehone the cylinders.

[John *.?-!.* cub owner]

My suggestion would be to take it to the shop and let them check. I prefer to let the shop do the rings, etc. I can do them, but the shop is better and quicker. I have had several done at local shop and always pay them the $25 or so they charge to install and gap the rings, whether they be standard, or it has been bored. Out of all the engines I have had done for me and friends the only problem I have ever had was low oil pressure on one, and it turned out to be my gauge.

[kmokgm]

Before going too far, check the Breather Tube from the front of the block to the Air Cleaner. Also insure the passageway in the block is open into the crankcase as well as the connector at the Air Cleaner.
I assume you are working on a Farmall Cub. The numbered series Lo-Boys did not have the vent tube to the air cleaner. Not sure why.

[TurboRoadster]

rings havent seated yet, open lower petcock on radiator, put garden hose in top of radiator, flow enough water to keep cold water circulating and draining out. While flowing the water, run the motor at a high idle for 30 minutes and see if they seal up.

[Steve Butram]

Wish you were closer. You could put it on the Cub Dyno and run it under a load.

[Bill Hudson]

Thanks for all the input, it is appreciated. Just a bit of an update, the owner has used the Cub this summer, primarily to move wagons/trailers around the nursery, and is pleased with the power and performance of the Cub. He has not mentioned the blowby as being a problem, so I'll let that sleeping dog lye.

I now have his TC unit on my workbench. We disassembled it enough to determine that the screen needed replacing. Parts are ordered and complete teardown and rebuild will happen when all parts are in hand.

Bill

[BigBill]

On the drag race engines I built once the oil pressure is up, the engine is up to operating temp, valves adjusted, timing set, carb adjusted its wide open throttle for 30 seconds to seat the rings. Never had any problems show up.

Your excessive blow by tells me it's the ring gaps are lined up or the ring gaps are too big.
Chrome rings take longer to seat under normal use.

Fact, my older new Husqvarna pro chainsaws were broken in right away. My new Husqvarna chainsaws took cutting twenty cords of firewood to break in. After being broken in the newer saws run awesome.