Welcome to the DoItYourself Forums!

To post questions, help other DIYers and reduce advertising (like the one on your left), join our DIY community. It's free!

Mechanical compression release


J A Boggan's Avatar
Visiting Guest

Posts: n/a

05-18-03, 10:17 PM   #1  
J A Boggan
Mechanical compression release

I have a Briggs and Stratton 5 Hp engine model - 124702, type - 3101-01 and code - 92061858. It dosen't have but 40 psi compression...could it have compression release. If it does, I've been told, that you could rotate it backwards to get a true reading on the compression. If this is true, could you explain how this works? Also, how can you determine if it has compression release or not? Thanks in advance.

 
Sponsored Links
cheese's Avatar
Forum Topic Moderator

Join Date: Jul 2001
Posts: 16,567
GA

05-19-03, 10:52 AM   #2  
I don't believe that engine has a compression release. It is OHV, correct? If so, check that the valves are not too tight.


"Who is John Galt?" - Ayn Rand (Atlas Shrugged)

God bless!

 
J A Boggan's Avatar
Visiting Guest

Posts: n/a

05-19-03, 02:43 PM   #3  
J A Boggan
Cheese, It's a L head. Is there anything to rotating it backwards. This is something I picked up in another forum.
Thanks,
JB

P.S. - I'm going to try a leakdown test also.

 
mikejmerritt's Avatar
Visiting Guest

Posts: n/a

05-19-03, 06:29 PM   #4  
mikejmerritt
Hey J A Boggan, there is not really a compression release as in a "part" that can fail on an L head Briggs that could cause poor compression. What they do have is a high spot on the back side of the exhaust cam lobe that lets the exhaust valve pop up just a bit as the piston comes up on the compression stroke. You can see this if you roll an engine through slowly watching the exhaust valve. It will jump up just a little about half way through the compression stroke. When the engine is being started, whether rope or electric, this action reduces the compression quite a bit allowing easy starting. Now you know where the famous Briggs "Easy Spin Starting" phrase comes from. All modern Briggs and Tecumseh L head engines use this system. Once running this action has little if any effect on compression. Compression tests run on these engines will be a bit low compared to true compression but you will be able to get an idea what it is and once running you can count on the compression being greater than when tested. It is true that this system is defeated by spinning the engine in reverse and is most accurate when using an electric impact wrench. Watch any old time small engine mechanic roll an engine through to check compression and he will always do it backwards.....Mike


Last edited by mikejmerritt; 05-20-03 at 03:15 AM.
 
cheese's Avatar
Forum Topic Moderator

Join Date: Jul 2001
Posts: 16,567
GA

05-19-03, 07:58 PM   #5  
Oops...I didn't look up your exact model#, just found one close, and it was an OHV. Mike is correct, and spinning it backwards will allow an accurate reading.


"Who is John Galt?" - Ayn Rand (Atlas Shrugged)

God bless!

 
Search this Thread