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Hi, I have an 18HP opposed twin horizontal Briggs engine on my racing mower. The engine runs fine and is in good condition. The only strange thing it does is it locks up when you turn it backwards by hand. It does it once per revolution, in the same spot. When it does lock, I can go forward just a tad, and it will "unlock" and I'll hear a click. I can then continue spinning it all the way around backwards. Its also strange that I can hear mechanical clicking noise as I turn the engine, either forward or backward. I think this noise is related to what is causing the locking. The noise goes away when the engine is running, and no other problems occur. I don't know if the engine has compression release, but if it does I think it might be the cause of the issue. Either that or the governor inside is acting up? Any advise? Thanks!!!

Pop off the top housing and look, your coil may be loose and this happens when the magnets pull it into the flywheel.

Thanks, I'll take a look. It really sounds like it's coming from inside the engine though, do you know if these have compression release?

Take off the valve chest covers and watch, feel the pushrods / cam followers.
Depending upon your grind, they can hang when going backwards.

That sounds more along the lines of what it is, I am off school next week I'll take the covers off and see if that's what it is. Thanks!

SleeperMower said:

That sounds more along the lines of what it is, I am off school next week I'll take the covers off and see if that's what it is. Thanks!

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If you have an OPPOSED twin you won't have pushrods...... Those twins are an L head type........ Now if you have a V-Twin Vanguard then that's a different animal......

Plus Tard......

Boudreaux In Eunice La. said:

If you have an OPPOSED twin you won't have pushrods...... Those twins are an L head type........ Now if you have a V-Twin Vanguard then that's a different animal......

Plus Tard......

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Could not remember if the twins had a short rod or a long follower, which is why the post read " pushrods / followers"
Only pulled down one twin and that was only to do a valve job.
Apart from that , the others have just been head gasket replacements on the left head.

However cam followers jambing on the cam when the engine runs backwards is a fairly common event, particularly on an older engine if you have been flogging it.
There was a bit of a guess that he had replaced the valves & springs with heavier ones without increasing the hardness of the cam face & followers.
I see this a lot in vintage motorcycles, owners fit stronger valve but ignore the rubbing forces that creates on the old cam.

On BSA B50's, it is also a very common occurance when the wrong followers are fitted.
Motor locks up solid if you try to turn it backwards.

All good points brought up, I'll check the cam followers and see if that is the issue. I'll keep you guys posted. Its funny I couldnt find anything online about cam followers causing the engine to lock, but I suppose most guys dont try to spin their engine backwards by hand... Thanks!

SleeperMower said:

All good points brought up, I'll check the cam followers and see if that is the issue. I'll keep you guys posted. Its funny I couldnt find anything online about cam followers causing the engine to lock, but I suppose most guys dont try to spin their engine backwards by hand... Thanks!

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Does your engine resmble this??

Yes, except its a horizontal shaft. Same engine

Has this engine been built as a race engine? There are some real weird camshafts for some Briggs engines. See flat cam lobes - by design - for longer duration. Might be something going on similar to this?

tom3 said:

Has this engine been built as a race engine? There are some real weird camshafts for some Briggs engines. See flat cam lobes - by design - for longer duration. Might be something going on similar to this?

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Hence the suggestion to check for the cam followers binding on the cam.

Seen a couple of grinds that would give you grief running backwards

I figured out the problem. The lighting/charging coil under the flywheel was hitting the magnets on the flywheel. The coil is damaged from it rubbing on the magnets. It was creating a "ratcheting" effect, allowing the engine to be turned one way, but not the other. I removed coil and solved problem. Its been a few months, but wanted to update in case anyone else has a similar issue. Thanks!!:thumbsup:

...wanted to update in case anyone else has a similar issue.

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Updates are always appreciated. Many times we are hit with "drive-by" posters who don't give
a rats behind.

Yes thanks always nice to update ! And I did not think at that at all well done