Silly question that i could not answer

[phillnjack2]

Today i got asked by my friend what are these plates on the side of his engine
His engine is a v4 140hp crossflow.
i said they are cover plates for the intake by pass ports
he then said, so what do they do and why are they there ?

i dont realy know why they are there and what they do to be honest

anyone know the benfit of these covers ?

what exactly is a by pass port ?
and why are they able to come open, and yet no covers on loop charged engines



phill..

 

[Auxlarry]

Re: Silly question that i could not answer

Have you taken one off? If you have you would notice the porting or what ever they call it, they aren't just a cover plate! I'll let one of the trained guys help explain this!! I'm just learning from these fine folks!!

Larry

 

[F_R]

Re: Silly question that i could not answer

You need to read up on how a two-stroke engine works. There is a ton of info out there. But very briefly, when the piston is on the upstroke, air & fuel is drawn into the crankcase. Then on the downstroke, that mixture is conpressed in the crankcase. When the piston gets near the bottom of the stroke, first the exhaust ports are uncovered, letting the exhaust out of the cylinder. Right after that, the intake ports on the other side of the cylinder open and the compressed fuel charge in the crankcase is blown into the cylinder. By now, the piston is on its way back up, compressing the charge in the cylinder. When it gets to the top of the stroke, a spark occurs, igniting the charge and pushing the piston back down.

On crossflow engines, the ports are drilled after the block is cast, and the covers seal up the access area. They also direct the charge into the ports. On loop charged engines the operation is similar except the ports are cast in place and aimed.

There is more to it than I just described. A little reading will be enlightening.

 

[HighTrim]

Re: Silly question that i could not answer

Frank while on this topic, why were the 50s OMCS 5.5hp CD and Fisherman models bypass covers not removable. How were they able to cast them together?

In additon to all that Frank mentioned, they also make a handy dandy spot to inspect the piston and rings.

 

[phillnjack2]

Re: Silly question that i could not answer

I know how a 2 stroke works and the difference between loopers and crossflows etc
just didnt know why these covers are there or what exactly was under there, it seemed too obvious to be just the transfer ports
but now it makes sense.

Seems strange that they drilled the ports after casting and then cover them up.
good for cleaning and tidying up the ports and like high trim says seeing the pistons and rings etc.
Might have to have a nosey round in there and see just how good or bad the port finnishing is, i would think better than
the cast in place ports being as these can easily be seen by the prospective owners of the engines !!!!!.


thanks for the info


phill

 

[F_R]

Re: Silly question that i could not answer

Frank while on this topic, why were the 50s OMCS 5.5hp CD and Fisherman models bypass covers not removable. How were they able to cast them together?

In additon to all that Frank mentioned, they also make a handy dandy spot to inspect the piston and rings.

Hm.m.m.m, good question. Hadn't thought about that. Of course the transfer passage would be no problem, just include that in the mold. But the ports still had to be drilled. Thinking about it, I wonder if they were drilled all the way through from the exhaust side (?) Of course they are not directly opposite the exhaust ports, but that could be handled by angleing the drill. Now I gotta check a block to see if that is what they did. I'll get back with you.

New technology perfected the lost foam casting method, making a lot of that stuff commonplace.

 

[F_R]

Re: Silly question that i could not answer

Follow-up....Yep, sure enough, they drilled the ports clear across from the exhaust side, at an angle so that the exhaust ports are higher in the cylinder than the intake ports. Furthermore, on the one I just checked (a 5hp Gale) after drilling through to create the intake ports, they re-drilled the exhaust ports with a larger drill.

So, mystery solved, and we all learned something today.

 

[HighTrim]

Re: Silly question that i could not answer

Cool, thanks. Interesting.

Would love to know their thinking on why they simply didnt make a removable bypass cover like all the other non 5.5hp models.