B7100 blow-by question

[AOW162435]

Hello again. Last year I posted about the new-to-me '79 B7100 I purchased (B7100).
Following a thorough going-through & servicing, I took it out to our property in WV and put to work pulling a 5' mower every few weeks. At the time, the tractor had 928 hours on the clock.
The tractor starts correctly, runs fantastic, has plenty of power, and generally does what I need it to do. When I first purchased it and ran it, the blow-by from the valve cover vent tube was minimal at best (completely normal from my experience). A few weeks ago, I suddenly noticed a much greater amount once bringing it to idle. It will rev up butter smooth and run at full RPM without an issue, but once dropped to idle, the blow-by will immediately start.

I have read many, many posts & write ups online, both from here as well as on other forums. The end result is that I'm no closer to figuring out if this is truly problematic, or more of a nuisance. I did read that the breather has a screen that can become clogged - I'm happy to remove the valve cover and do so.

But based on my write-up, can anyone offer a fresh perspective on the matter? At this point, the tractor has around 950 hours.


Andreas

 

[TheOldHokie]

Hello again. Last year I posted about the new-to-me '79 B7100 I purchased (B7100).
Following a thorough going-through & servicing, I took it out to our property in WV and put to work pulling a 5' mower every few weeks. At the time, the tractor had 928 hours on the clock.
The tractor starts correctly, runs fantastic, has plenty of power, and generally does what I need it to do. When I first purchased it and ran it, the blow-by from the valve cover vent tube was minimal at best (completely normal from my experience). A few weeks ago, I suddenly noticed a much greater amount once bringing it to idle. It will rev up butter smooth and run at full RPM without an issue, but once dropped to idle, the blow-by will immediately start.

I have read many, many posts & write ups online, both from here as well as on other forums. The end result is that I'm no closer to figuring out if this is truly problematic, or more of a nuisance. I did read that the breather has a screen that can become clogged - I'm happy to remove the valve cover and do so.

But based on my write-up, can anyone offer a fresh perspective on the matter? At this point, the tractor has around 950 hours.


Andreas

Fix it till you break it

Dan

 

[85Hokie]

Blow by as you as you know full well is gases that are getting by the rings.

This may sound a bit counter intuitive - but running it harder, longer will make for a better engine.

Low speed = low temps - low temps are very bad!! As my physics teacher in HS said - if you could run a car at much higher temps, it would be more efficient. BUT we cannot.

The blow by cannot be "fixed" in an easy way - a rebuild is the true answer. BUT, if compression is good enough cold = then run it and don't worry about it UNTIL such time it does not start easily.

 

[TerryKing]

I suddenly noticed a much greater amount once bringing it to idle. It will rev up butter smooth and run at full RPM without an issue, but once dropped to idle, the blow-by will immediately start.

Hi Andreas, Not sure what is happening here... Hmmmm..

I've worked on many (older, like me) cars and trucks with engines worn enough to have some blow-by. Rebuilt a few.

I usually (always?) saw blow-by increase under load (like revving a gas engine). Higher combustion pressure.

MAYBE the rings are imperfect, but the higher combustion pressure under load "seats" the rings better??

I will try to check my B7100HST when I run it again.. So right now: Hmmmmm...

 

[AOW162435]

Would it be of any help if I take a video of what I'm seeing?

Andreas

 

[AOW162435]

Over the last few days, I mowed for around 5 hours total. Very steep fields & meadows (our property and two neighbors). I kept 85Hokie's comment in mind about running it hard... The tractor definitely got a workout cutting 4' high growth and going up slopes I can barely walk up.
I made sure to stop every so often to clean the radiator screen of accumulated milk weed fuzz, etc., and topped off coolant every morning.
I think I was hoping for some sort of miracle but the blow by is just as bad or even more. As stated earlier, it's not really visible while plowing along at full steam, but as soon as I throttle down and come to a stop, it sends a steady stream of vapor out of the hose.

Would really like a few more thoughts on what could have brought this on out of the blue. It really is a nice example (~960 hrs) and runs so well. While I'm not up for tearing the engine down myself, I'd have no issue pulling the front axle / frame away in order to fully expose the engine.


Andreas

 

[TheOldHokie]

Over the last few days, I mowed for around 5 hours total. Very steep fields & meadows (our property and two neighbors). I kept 85Hokie's comment in mind about running it hard... The tractor definitely got a workout cutting 4' high growth and going up slopes I can barely walk up.
I made sure to stop every so often to clean the radiator screen of accumulated milk weed fuzz, etc., and topped off coolant every morning.
I think I was hoping for some sort of miracle but the blow by is just as bad or even more. As stated earlier, it's not really visible while plowing along at full steam, but as soon as I throttle down and come to a stop, it sends a steady stream of vapor out of the hose.

Would really like a few more thoughts on what could have brought this on out of the blue. It really is a nice example (~960 hrs) and runs so well. While I'm not up for tearing the engine down myself, I'd have no issue pulling the front axle / frame away in order to fully expose the engine.


Andreas

My thoughts:

You just worked the snot out of your 35-50 year old tractor cutting 4 foot high vegatation on mountain goat trails. The tractor performed flawlessly but when done you observed visible vapor at the crankcase breather.

 

[InTheWoods]

...The blow by cannot be "fixed" in an easy way - a rebuild is the true answer. BUT, if compression is good enough cold = then run it and don't worry about it UNTIL such time it does not start easily.

Yep - no easy fix.

Just keep an eye on your oil level, as it is possible to blow out crankcase oil with excessive blowby...

 

[85Hokie]

one thing that will scare you - IF you fill the radiator up TOO much, it will spew OUT via the hose that goes to the whistle ....and you will smell radiator fluid.......

The fluid in the radiator should be about an inch below the fill top - covering the top of the fins.

Remember this - the fluid works on expansion caused by heat = as the water gets hot it will rise, comes up the top hose and falls through the radiator.

Get you an infrared thermometer - get the tractor good and hot, run the snot out of it.

SHOOT the top neck of the radiator while running - should be 195-210 F......... shoot the bottom neck, should be about 80 to 100 F LOWER.

And that vapor trail the Old Hokie mentioned ............. hell that is a good sign!!

If it starts easily with glowing and runs well - keep the radiator clean and it will go ANOTHER 960 hours!!!!

 

[GeoHorn]

Don’t really “shoot” the radiator top and bottom or you will definitely have a radiator leak problem.

It may be that a stuck piston ring (or several) may be the cause of low-speed blow-by. Working the engine hard May resolve this after some time. There may be some folks who will encourage you to try various “mystery oils” or “snake oils”… but I’m not a proponent of those.

I think you have a good running tractor and that if you regularly check and maintain fluid levels for safety…. the little tractor may “cure” itself by simply being used regularly. Don’t be too hasty to tear into it unnecessarily. IMO