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...