Jump to content
Westie1

Exhaust valve opening on compression stroke

Recommended Posts

Morning all,

Just been turning the engine over by hand and I have valve lift on what i think is the compression stroke.

Would adjusting the valves stop this or is it designed this way.

Thanks

Found out it's compression release for anyone wondering the same.

Screenshot_20190118-100711_Chrome.jpg

Share this post


Link to post
Share on other sites

Quite normal. Some manufacturers do it with a centrifugally retracted pin altering the cam profile while others do it  with the cam profile itself.

Some do it on the inlet, some on the exhaust and one at least, on both.

Share this post


Link to post
Share on other sites

Never heard of it before and I thought how the hell does the cam change if it does lol, amazing really.

Got the head back on now and hopefully when I've got it rewired it will run bob on.

Share this post


Link to post
Share on other sites

You will also find that older Briggs & also Tecumseh engines around 5hp open the exhaust valve slightly on compression. As the engines wear this can cause starting issues due to low compression. On OHV engines I have countered this by increasing the gap on the exhaust valve & on side valve engines I have removed the exhaust valve & ground a bit off the valve stem (not too much).  I am sure Wristpin will not necessarily approve of this practice but it has worked for me on several occasions.

Share this post


Link to post
Share on other sites
8 hours ago, Fix'em all said:

You will also find that older Briggs & also Tecumseh engines around 5hp open the exhaust valve slightly on compression. As the engines wear this can cause starting issues due to low compression. On OHV engines I have countered this by increasing the gap on the exhaust valve & on side valve engines I have removed the exhaust valve & ground a bit off the valve stem (not too much).  I am sure Wristpin will not necessarily approve of this practice but it has worked for me on several occasions.

Hmm !!!

Approval  or not ,  increasing the gap by any means is counterproductive as far as compression release for easier starting is concerned. The bigger the gap, the less effective, whatever the release method. That said, a really knackered ( technical term) engine may benefit from all the compression that can be found. AKA an elegant, albeit unorthodox, engineering solution!

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×
×
  • Create New...