Topic: 2 sohc4 sync port screws found matched to runners except on cyl 2, coincidence?

[RFogelsong]

I'm currently restoring a cb400f and cb350f and while inspecting the inlet ports after removing the rubber carb connectors, I noticed that all of the sync port block off screws except cyl #2's were all pretty well matched to their ports.  I'd say cyl #2's screw was protruding 1-2 mm, or, enough to catch/scratch the pad of my finger while feeling inside the port.  It's the same on both engines, with #2 protruding about how much I expected them all to stick through in stock configuration from the reports and pictures across the forum. 

I wouldn't think anything of this if it was only on my 400, which, from what I gather, was probably a track bike for a while and could have had a "matched" screw set, with one replaced in the heat of a moment, now showing in the #2 runner, but since it's EXACTLY the same on the 350f, I believe this is likely how they came stock.  Variation in port geometry/wall thickness/un-symmetric casting? 

This is kind of inconsequential, especially on a stock engine, but it sticks into the airflow enough that I think grinding this screw down so that it matches the others might actually make a difference in evening power production across the cylinders.  I figured they'd all be long or they'd all be short/matched, one way or the other, not both.  If it makes a difference anywhere, it'd be on the smallest ports/engine of the series.

I definitely want them to be the same, since I'm there.  It might be inherent and unique to the small-four motor (these two are my first experience with the small sohc platform), but I thought it might be worth calling to the attention of a group that COULD verify/refute/tell me it doesn't matter anyway.

To attempt to answer my own question, I plan to take both bikes to a local shop that has a dyno and egt each head pipe (both running 400f pipes) to ensure my a/f mixtures are even across all cylinders once I get both bikes put together.  This type of instrumented testing (individual cyl. meas. devices) would be the level I think would be required to measure any difference from a mod like this...and it still might be lost in noise...and it's not the primary purpose (really, it's just to tell me if I cleaned all four carbs the same and what direction it needs to go, if any), but as a side-benefit, it'll provide insight to this question. 

[BenelliSEI]

Bizarre........ just shorten the screw. I seriously doubt that’s an engineered solution! Try checking a parts manual. If there is a separate part number, perhaps?

[754]

 Add a washer.
 And dont worry,  cuz if you do, then you must take rubber molds of your ports next, and start comparing them.. and there is more. .

[TwoTired]

Originally the port screws had thick-ish aluminum washers.

I don't think they should protrude into the intake port runner.  Everything else they did was geared toward clean smooth airflow where econmical.

Cheers,

[RFogelsong]

Of course, idk why I was going to grind down a screw rather than adding a washer...such a simple solution and that's definitely all it'll take.

This made me wonder if I was maybe missing the washers on those cylinders...went out to the garage, nope...all silver stock ones were there.  I'll get some beefy copper ones for them when they go back together.

[754]

It may be different lengths over the years.
 I lost one, one day...used a later one.  They used brass some years  aluminum others. 

[RFogelsong]

Add a washer.
 And dont worry,  cuz if you do, then you must take rubber molds of your ports next, and start comparing them.. and there is more. .

O.O tell me more!!!

I would love to be able to find a white paper on the evolution of the Honda port designs and angles.  Flow stuff is really interesting...as an aerospace engineer.

I worked on vintage motorcycles last summer full time to fill out the mechanical side of the theoretical engineering background.  Everyone thinks he's a mechanic...  After wrenching on many different brands, and many different Hondas, it's funny how similar mechanisms are across Hondas DECADES apart.  Some of that is thoughtful, some of it is thriftiness and long-term manufacturing investment, but from what I know about Honda's evolution in capabilities throughout the CB-era, they were frequently labeled the best at casting and manufacturing their own parts. 

I've found a few key names across the 60's to 80's Honda timeline that make me wonder if casting techniques or geometries developed or discovered in the 60's gp era led to methods enabling mass production of our CB's or even my VF's...or possibly restricting us from doing what we really want...the published diagrams from the RC30 hrc race mods manual paint a fuller picture of this sort of thing, for its use case. 

Honda released the new super cub recently and the press was quoting a line about how, around the time of the original cub/super-cub launch (didn't read too closely), Honda quadrupled the power of the next most popular available engine on the market at the time from 1 to 4 hp.  They said they did this, basically, through the use of larger valves.  With Honda being such a 4 stroke rooted company from the start, it sounds like most of the story of the cool technical developments of Honda lie in the head and port design and flow characteristics and casting techniques.  I think we need a friend that speaks Japanese... 

[Tracksnblades1]

Add a washer.
 And dont worry,  cuz if you do, then you must take rubber molds of your ports next, and start comparing them.. and there is more. .

O.O tell me more!!!

I would love to be able to find a white paper on the evolution of the Honda port designs and angles.  Flow stuff is really interesting...as an aerospace engineer.

I worked on vintage motorcycles last summer full time to fill out the mechanical side of the theoretical engineering background.  Everyone thinks he's a mechanic...  After wrenching on many different brands, and many different Hondas, it's funny how similar mechanisms are across Hondas DECADES apart.  Some of that is thoughtful, some of it is thriftiness and long-term manufacturing investment, but from what I know about Honda's evolution in capabilities throughout the CB-era, they were frequently labeled the best at casting and manufacturing their own parts. 

I've found a few key names across the 60's to 80's Honda timeline that make me wonder if casting techniques or geometries developed or discovered in the 60's gp era led to methods enabling mass production of our CB's or even my VF's...or possibly restricting us from doing what we really want...the published diagrams from the RC30 hrc race mods manual paint a fuller picture of this sort of thing, for its use case. 

Honda released the new super cub recently and the press was quoting a line about how, around the time of the original cub/super-cub launch (didn't read too closely), Honda quadrupled the power of the next most popular available engine on the market at the time from 1 to 4 hp.  They said they did this, basically, through the use of larger valves.  With Honda being such a 4 stroke rooted company from the start, it sounds like most of the story of the cool technical developments of Honda lie in the head and port design and flow characteristics and casting techniques.  I think we need a friend that speaks Japanese...

+1,

And many remember Honda's mark they left inthe 2 Stroke world.
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