Thread: Series IIa Motor Rebuild.

The I had a similar problem with a rebuilt engine many years ago, and after reading your post today I remembered the cause. I don’t know how long your engine was out for repair and the reason for the rebuild so I may be off the mark but is your exhaust system causing a restriction. The symptoms are similar lack of power and black smoke under load also if run long enough engine temperature can rise, quickly and very high as the engine cannot get rid of the heat. The engine also cannot breath and will not pull in a full charge of air due to valve overlap which occurs at the end of the exhaust stroke. At this time the exhaust valve is held open just long enough to assist in drawing air into the cylinder with the inlet valve just opening.Sounds silly but in normal operation the exhausting gas will create a small vacuum in the cylinder thus assisting in purging the cylinder and drawing in the air fuel mixture.
So before you do too much more check exhaust flow, it may sound good idling in the yard but can be blocked, a drive up the road with someone following should tell you it will sound restricted. If you canÂ’t do that another way is too install a mercury manometer into the exhaust manifold or a water manometer in to the inlet manifold and check flow. The inlet manifold should show a vacuum when running, after checking inlet vacuum during a drive up the hill then disconnect the exhaust and retry if there is no blockage the vacuum will be the same or very similar if there is a big difference I would suspect a restriction in the exhaust.
And if using a manometer in the exhaust manifold you will se a high reading if the exhaust is blocked.
Hope this makes sense and assists you Gippy

That sounds like a definite possibility Gippy. I'll grab my neighbour this afternoon when I get home and see if his observations can shed light any light on your theory. Thanks for the heads up.

Originally Posted by Gippslander

The I had a similar problem with a rebuilt engine many years ago, and after reading your post today I remembered the cause. I don’t know how long your engine was out for repair and the reason for the rebuild so I may be off the mark but is your exhaust system causing a restriction. The symptoms are similar lack of power and black smoke under load also if run long enough engine temperature can rise, quickly and very high as the engine cannot get rid of the heat. The engine also cannot breath and will not pull in a full charge of air due to valve overlap which occurs at the end of the exhaust stroke. At this time the exhaust valve is held open just long enough to assist in drawing air into the cylinder with the inlet valve just opening.Sounds silly but in normal operation the exhausting gas will create a small vacuum in the cylinder thus assisting in purging the cylinder and drawing in the air fuel mixture.
So before you do too much more check exhaust flow, it may sound good idling in the yard but can be blocked, a drive up the road with someone following should tell you it will sound restricted. If you canÂ’t do that another way is too install a mercury manometer into the exhaust manifold or a water manometer in to the inlet manifold and check flow. The inlet manifold should show a vacuum when running, after checking inlet vacuum during a drive up the hill then disconnect the exhaust and retry if there is no blockage the vacuum will be the same or very similar if there is a big difference I would suspect a restriction in the exhaust.
And if using a manometer in the exhaust manifold you will se a high reading if the exhaust is blocked.
Hope this makes sense and assists you Gippy

Well how did it go we’re you able to resolve the issue, I hope you have would be great to hear a result.

gippy