Antique Engines and Old Iron
[Home] - [HELP] - [Forums] - [Library] - [Photo Gallery] - [Groups] - [Classified Ads] - [Subscribe] - [Links] - [Books] - [Sponsors] -

Go Back   SmokStak > SmokStak® Antique Engine Community > Antique Gas Engine Discussion > Antique Engine Archives
Forgot Password? Join Us!


Antique Engine Archives All archived posts from 1999 to 2004 when SmokStak was on EnginAds. This is a read-only board.

Antique Engine Archives

What to do about blowby?

this thread has 13 replies and has been viewed 34232 times

Thread Tools Display Modes
Old 12-22-2004, 03:35:22 PM
Mac Leod Mac Leod is offline
Join Date: Nov 2004
Location: California USA
Posts: 753
Thanks: 0
Thanked 44 Times in 35 Posts
Default What to do about blowby?

ok, on my Jaeger the cylinder was honed and the piston was put back in with the old rings (6 0f them) the engine ran well after the rings took a seat. after a few months running occasionaly there is a noticable amount of blow by. I see no reason for this to start now, any ideas why...what can I do?


Mac Leod
Sponsored Links
Old 12-22-2004, 04:40:50 PM
Junkologist's Avatar
Junkologist Junkologist is offline
Join Date: Nov 2004
Location: Avon, Ohio, USA
Posts: 4,395
Thanks: 3,064
Thanked 3,773 Times in 1,687 Posts
Images: 160
Default Re: What to do about blowby

I have never had any luck reusing old piston rings. I know a lot of people that do it, though. If I don't have to pull the piston out of an engine, I don't. If I have to, I replace the rings. The rings are probably one of the cheapest parts you can get for an engine. Unless, of course, you're working on something with a huge bore. If I were you, I would get a new set of rings and lightly hone the cylinder to break the glaze, if there is any, since you said you honed it not long ago. You should also check the side clearance of the rings in the grooves. If that is excessive, compression can leak around the back side of the rings.

Some engines are funny when it comes to blowby. I have a Fairbanks headless "Z" that has no blowby sometimes and other times you'd wonder if it had rings in it at all! I think there is a multitude of things going on in my engine, such as, worn piston, worn ring grooves, the cylinder probably has taper and is out of round. I did just recently renew the wrist pin, and it seems to have helped it a lot by possibly keeping the piston a little more true in the cylinder instead of letting do it's own thing due to the sloppy wrist pin and bushing. These are my experiences, take them for what they're worth.

Happy holidays!

Old 12-22-2004, 05:46:22 PM
Posts: n/a
Default Re: What to do about blowby

there might be a lot of end gap on the rings and once and a while the end gap on all the rings get lined up with one another and the compression just blows right through the end gap.

just a thought

Old 12-28-2004, 12:01:57 AM
Andrew Mackey Andrew Mackey is online now
Join Date: Nov 2004
Location: Rockaway, New Jersey USA
Posts: 13,564
Thanks: 1,926
Thanked 6,283 Times in 4,058 Posts
Default Re: What to do about blowby?

Hi Mac,
Above post is probably spot on, worn rings in a honed cylender wear even more and faster! The end gaps are probably aligning now and then. Is oil or air blowing back in to the oiler? Is oil getting to the piston - 5 to 6 drops a minute? Is the piston wet with oil when the engine is running, or does it appear to be dry? Is oil being blown off the rear of the piston? If you pull the engine over smartly, does it blow by? Or does it only blow by at slow speed? So many questions! If the piston is wet, and the blow by is not noticeable at running speeds, don't worry about it. If it is noticeable at running speed, and or if the piston is running dry, you will have to remedy, and soon, if you want to save the piston and bore. Running dry, and hot leads to extreme wear and fast! Check your piston to cylender clearances - if the piston is too sloppy in the bore, the rings will not be able to seal correctly.
Old 12-28-2004, 01:33:54 AM
Mac Leod Mac Leod is offline
Join Date: Nov 2004
Location: California USA
Posts: 753
Thanks: 0
Thanked 44 Times in 35 Posts
Default Re: What to do about blowby?

with six rings the gaps lineing seems a bit unlikely to me (my opinion not worth much, only had a H&M for a year now). every now and then the oiler wil have air blow back. the piston is geting about 15 drops per 10 or so the bottom of the cilinder had no oil. is too much oil possible, gummed up the rings? never does any work, have nothing for it to run. oil is not blown off the rear of the piston in any great quantity, just a puff of exhaust from the top of the cylinder/piston when it fires.

any more info needed to evaluate the situation?

Mac Leod
Old 12-28-2004, 12:14:50 PM
PistonRing's Avatar
PistonRing PistonRing is offline
Banner Sponsor
Join Date: Oct 2004
Location: Elkton, MD USA
Posts: 291
Thanks: 354
Thanked 501 Times in 119 Posts
Exclamation Re: What to do about blowby?

Hi Mac-
When you honed the cylinder you forced the old rings to get about 20 years of accelerated wear in a days time. By introdicing this much wear you most likely wore the rings much past the point of working "acceptably". Had you not honed you could have probably gotten away with it. In any case there has been a past compression problem with your engine. Having 6 rings in it tells me that some past owner was trying to get better compression than he had by doubling up. Usually doubling up doesn't work any better or worse than single rings and is only a desirable solution where the proper width single ring is not readily available. Check your ring side clearances. This is likely your problem area. Expect to see an extra 1.5 thou of clearance due to using the doubled rings. With 2 per groove you should have 3 thou when new, and 6.5 thou is the max. Seven or more and you need machine work. The top groove always wears the most. You need a set of three rings 3 1/4" x 1/4". And probably three .030" spacers to go on the top side of the rings. Measuring with feeler gauges will tell the story. When the rings are not held tightly enough in the ring grooves due to wear the rings can turn in the grooves. The force gravity makes the gaps all line up at the top in a horizontal engine much like a marble finding the bottom of a punch bowl when released. Maybe not quite this fast but faster than you might imagine. In any case the compression doesn't escape past the lined up gaps. 95% of the leakage is by the sides of the rings where they don't lay flat against the ring land. End gap means very little in the business of sealing compression. It can however indicate a ring that is not the proper size for the cylinder and tip you off that the ring may not be round for the desired cylinder diameter.
The two big problem areas today are:
#1. The thing that is way overdone to engines is honing. If you want to save yourself a lot of headaches skip this step. If the cylinder is not rusty or is not a newly bored cylinder you are better off not to hone.
#2. NOT checking the side clearance in the ring grooves. 5 thou is the max acceptable. Any more and compression problems are coming to your neighborhood shortly.
Recommended reading:
Good luck in your quest for compression. Give me a call or email and I will be glad to help.
Thank you,
Dave Reed
Otto Gas Engine Works
2167 Blue Ball Road
Elkton MD 21921-3330
phone 410-398-7340
Old 12-28-2004, 12:26:11 PM
Ken Majeski's Avatar
Ken Majeski Ken Majeski is offline
Join Date: Oct 2004
Location: South Lawton, Wisconsin
Posts: 2,808
Thanks: 1,583
Thanked 2,414 Times in 835 Posts
Images: 46
Default Re: What to do about blowby?

Well..... If the cylinder/rings/piston is worn at all it will depend on oil to help Seal the rings. AND if you flood the engine when starting it once oil will be washed off and once it starts to blow by it will keep the oil from getting to the proper place. Sort of a No Win situation. Does the oiler have a Check Ball in it.???? Sometimes blowby will keep the oil from going down the pipe to where it is supposed to be.

If the piston is worn too much or the cylinder is tapered the piston will Cock in the bore and the rings will not seat. If you have good compression when turning it one way and much less when turning it the other way I would expect to find excessive wear.
Ken Majeski, Ellsworth Wis.
Old 12-28-2004, 02:02:10 PM
Simple_serf Simple_serf is offline
Join Date: Nov 2004
Location: Jamestown, New York USA
Posts: 147
Thanks: 0
Thanked 8 Times in 4 Posts
Default Re: What to do about blowby?

My FMZ Has a massive amount of compression, but at tdc it has a bit of blowby. My Novo is the same way. Granted, the FMZ only has about 2 hrs on it since honing... I put new rings in it, I think the rings were $5 each and the engine uses three. For the amount of trouble they can cause it is really easier to just put on a new set of rings. If you do this, then honing to break the glaze is a good idea. I run this engine with the oiler up as high as I can without smoke coming out the exhaust, not surprisingly it is just a few drops per minute over what Fairbanks recomended.

The simple serf
Old 12-30-2004, 04:28:45 PM
hit-n-miss166922 hit-n-miss166922 is offline
Join Date: Nov 2004
Location: Waukesha, Wisconsin USA
Posts: 92
Thanks: 4
Thanked 3 Times in 1 Post
Default Re: What to do about blowby?

Hello fron Wisconsin!!!
All replays are excellant, The only thing that I would use instesd of a hone is a bottle brush type hone, you know the one with the little balls. They break the glaze but do not change the size and never chatter. Also will follow the taper or out of roundness of the cylinder. I like using them!!!!
Old 12-30-2004, 05:40:47 PM
Mac Leod Mac Leod is offline
Join Date: Nov 2004
Location: California USA
Posts: 753
Thanks: 0
Thanked 44 Times in 35 Posts
Default Re: What to do about blowby?

I still see no reason for the rings to seat so well and then have blowby a short while later other than the ring gap lineing up...seems to have compression when I turn it over backwards, very little blowby

Mac Leod


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

F o r u m Jump

Similar Threads Chosen at Random
Thread Thread Starter F o r u m Replies Last Post
Engine Blowby TomH Antique Gas Engine Discussion 7 07-26-2005 04:12:01 PM

Use "Ctrl" mouse wheel to change screen size.
All times are GMT -4. The time now is 03:43:38 PM.

Smokstak and Enginads site search!

All use is subject to our TERMS OF SERVICE
SMOKSTAK® is a Registered Trade Mark - A Community of Antique Engine Enthusiasts
Copyright © 2000 - 2016 by Harry Matthews P.O. Box 5612 - Sarasota, FL 34277