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#439251 - 06/08/12 9:31 pm A65 Head Flow - Match The Ports  
Joined: Jan 2006
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Gary E Offline
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Gary E  Offline
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Medford, Oregon
Currently rebuilding the engine. What are experiences with flowing and matching the ports on A65 ('68) heads. This engine will be not used in competition. I plan to balance the bottom end.

Not interested in specifically enlarging the ports, only want to match the flow to each side. Are the stock ports and combustion chambers already close enough that little can be gained, or is there room for improvement?


1967 BSA Wasp
1967 BSA Hornet (West Coast Model)
1967 BSA Hornet (East Coast Model)
1968 BSA Firebird Scrambler
1968 BSA Spitfire Mark IV
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#439270 - 06/08/12 10:48 pm Re: A65 Head Flow - Match The Ports [Re: Gary E]  
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Pete R - R.I.P. Offline
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I'd say very little to be gained,apart from a good job on the valve seats.
The round part of the port is too big already.All the restriction is at the valve,until you get up around 1/2" valve-lift (and you won't get that much lift).

At 1/2" lift,the valve can flow about as much as a 29mm round port.At that point,you could justify removing some metal near the valve guide and squaring the port in that area (as much as you can),because that area would then be slightly more restrictive than the valve and the round part of the port.It's hardly necessary,with any normal valve lift.

It won't hurt to match the ports to the carbs,but that's probably good already.

#439290 - 06/09/12 12:09 am Re: A65 Head Flow - Match The Ports [Re: Gary E]  
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Gary E Offline
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Gary E  Offline
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Medford, Oregon
Thanks for the info Pete. I'm not interested in making the ports larger. My primary interest is to match the flow for both cylinders. Each side is flowed and the lowest flow side is then matched to the side with the largest flow. Secondary interest is to smooth the roughness of the ports. I'm not really interested in removing material (other than matching the flow), or changing the shape of the ports or combustion chamber.

I'm sure others have already been there, done that, of what I am considering, so interested in knowing if noteworthy gain is possible.


1967 BSA Wasp
1967 BSA Hornet (West Coast Model)
1967 BSA Hornet (East Coast Model)
1968 BSA Firebird Scrambler
1968 BSA Spitfire Mark IV
#439303 - 06/09/12 12:35 am Re: A65 Head Flow - Match The Ports [Re: Gary E]  
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Mark Parker Offline
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Bega NSW Australia
I don't think its something you need do, you could blend and smooth but it wouldn't be very noticable, doing the valve seats with a good 3 angle will improve it.


mark
#439418 - 06/09/12 7:53 pm Re: A65 Head Flow - Match The Ports [Re: Gary E]  
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Richard Phillips Offline
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San Luis Obispo, CA
Gary,
Match the intake ports to each other, then match the gaskets to the intake port.
Richard

#439429 - 06/09/12 9:30 pm Re: A65 Head Flow - Match The Ports [Re: Richard Phillips]  
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Gary E Offline
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Medford, Oregon
Originally Posted By: Richard Phillips
Gary,
Match the intake ports to each other, then match the gaskets to the intake port.
Richard

Exactly. That is what I would like to do if I hear from someone that has actually bench flowed, for volume, an A65 head, to see if their is a difference worthy of doing it.


1967 BSA Wasp
1967 BSA Hornet (West Coast Model)
1967 BSA Hornet (East Coast Model)
1968 BSA Firebird Scrambler
1968 BSA Spitfire Mark IV
#439446 - 06/09/12 11:39 pm Re: A65 Head Flow - Match The Ports [Re: Gary E]  
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Richard Phillips Offline
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Richard Phillips  Offline
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San Luis Obispo, CA
I think all you need to do is match the ports, flowing them can get tricky if you do not have a flow bench.

#439452 - 06/10/12 12:03 am Re: A65 Head Flow - Match The Ports [Re: Gary E]  
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Gary E Offline
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Gary E  Offline
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Medford, Oregon
Really difficult to match the ports by eye. I've got a flow bench available.


1967 BSA Wasp
1967 BSA Hornet (West Coast Model)
1967 BSA Hornet (East Coast Model)
1968 BSA Firebird Scrambler
1968 BSA Spitfire Mark IV
#439466 - 06/10/12 1:18 am Re: A65 Head Flow - Match The Ports [Re: Gary E]  
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Richard Phillips Offline
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Richard Phillips  Offline
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San Luis Obispo, CA
I use calipers, and blue die, then draw it out. Flow bench is very cool. You don't need to do much cutting, just balance. I

#439479 - 06/10/12 3:47 am Re: A65 Head Flow - Match The Ports [Re: Gary E]  
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Mark Parker Offline
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"I've got a flow bench available." It would be interesting to see what the std head flows. I wish someone around here had one.


mark
#439515 - 06/10/12 2:00 pm Re: A65 Head Flow - Match The Ports [Re: Gary E]  
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Gary E Offline
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Gary E  Offline
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Medford, Oregon
Unless I read otherwise I may have to step up and find out how a standard head casting fairs in terms of flow to each side. I'm sure others have already been there, done that.


1967 BSA Wasp
1967 BSA Hornet (West Coast Model)
1967 BSA Hornet (East Coast Model)
1968 BSA Firebird Scrambler
1968 BSA Spitfire Mark IV
#439527 - 06/10/12 3:11 pm Re: A65 Head Flow - Match The Ports [Re: Gary E]  
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Magnetoman Online content
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Originally Posted By: Gary E
What are experiences with flowing and matching the ports on A65 ('68) heads. This engine will be not used in competition.
I have my own flow bench in the garage and have read just about everything on the topic I could get my hands on. With that as background, and with your stated application of the bike in mind, my advice would be to leave the head alone.

Air flow does not do what people intuitively think it does, so anything you do to a head in the hopes of making things better is at least as likely to reduce the flow as it is to increase it. Even with a flow bench, what do you do when you remove some metal in the hopes of increasing flow, and the flow actually decreases? You can't put the metal back (yes, there's epoxy, but you will forever wonder if/when it is going to come loose and be sucked into the engine).

Someone who specializes in, say, porting A65 heads will have ruined more than one in the process of teaching himself what works and what doesn't for that particular head (for learning purposes, it's OK to use epoxy). There are some fuzzy general principles to porting, so the knowledge gained from an A65 head will be a good starting point for porting a Bonneville, but changes will be needed.

The most important thing for anyone is to have a smooth inlet track from the carb to the head. This is something everyone can and should do, and it requires no special tools. The track does not have to be smooth as in polished, but it has to be without any steps whatever -- especially along the bottom of the inlet track -- at the various joints (before anyone mentions it, a Gold Star with a GP is a special case where performance at idle isn't important).

When starting and at idle the fuel enters the airstream from two tiny holes at the rear of the slide. That fuel hugs the bottom of the track for some distance and, if it encounters a gasket protruding only an insignificant 1/16" into the stream, the flow will be disrupted and it is likely your life will be miserable until you fix this problem. At anything beyond idle this step doesn't matter, so the carb will be well behaved at all times other than when trying to start it. Some of the problems blamed on clogged pilot jets -- and indeed these problems are very real -- very likely are caused by slightly misfitting gaskets (and/or a mismatch to the inlet on the head). Because this involves turbulent airflow, whose behavior is non-intuitive, it is possible on a given bike for the gasket to protrude without causing a problem with starting. However, while a protruding gasket may or may not cause problems for a particular bike, making sure it doesn't protrude is very easy and ensures there won't be a problem.

Also, the carb is held by two studs passing through fairly wide clearance holes in the carb. Even if you match the hold diameter of the gasket and the carb perfectly, the clearance of those holes means one time you mount the carb the gasket could be a bit low (which would be fine), but the next time it could be a bit high, protruding into the airstream at the bottom. The same applies to the inlet to the head where, even if of identical diameter to the carb, the clearance means the carb could be mounted a bit too high one time, and a bit too low the next time. There's nothing like a "hidden variable" like this to drive someone insane when trying to solve a starting/jetting problem. After mounting the carb, simply run your finger or a popsickle stick along the bottom surface to check that nothing is protruding.

#439534 - 06/10/12 4:20 pm Re: A65 Head Flow - Match The Ports [Re: Gary E]  
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Gary E Offline
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Gary E  Offline
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Medford, Oregon
Mag,

Thanks for the info. I concur with most of what you have provided, from experience with aircraft heads (experimental category), VW (sand rail) engines, drag boat engines (Chev. & Mopar), as well as V8 (Chev.) engines for drags, over the years. Never used epoxy for build up of ports. With alloy heads such as VW, we welded 'em up and made the changes. And yes, a lot were throw aways as some ideas didn't work out; that's the R&D or experimental part.

Gasket ridges and port lumps are a basic given in port/carb. tuning, and is useful to all who assemble there own engines.

But, again, what I'm interested in knowing is how equal or non-equal is the flow in a standard, non-molested A65 68-701 head? Then I can decide if flow match improvement is worthy of consideration. You have a flow bench. Have you done any flow measurements on a stock A65 head? If so, what were the results of that work?


1967 BSA Wasp
1967 BSA Hornet (West Coast Model)
1967 BSA Hornet (East Coast Model)
1968 BSA Firebird Scrambler
1968 BSA Spitfire Mark IV
#439549 - 06/10/12 5:07 pm Re: A65 Head Flow - Match The Ports [Re: Gary E]  
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Magnetoman Online content
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Originally Posted By: Gary E

But, again, what I'm interested in knowing is how equal or non-equal is the flow in a standard, non-molested A65 68-701 head? Then I can decide if flow match improvement is worthy of consideration. You have a flow bench. Have you done any flow measurements on a stock A65 head?
Unfortunately, I'm sure I'm unique amongst everyone on this forum in having too many projects, and too little spare time... The closest I've come to the measurement you would like is with stock A10 heads, and even there I don't have results yet. I have one of the rare dual-carb A10 heads so, naturally, I can't help wondering if it actually flows any better than a stock head. I machined the necessary adapters and dummy A10 cylinder for mounting A10 heads on my Superflow bench, fabricated a micrometer adjustable variable valve opening assembly (necessary for measuring flow vs. lift), and made one quick run on one of the heads to confirm I had worked out the kinks. That was two years ago and I haven't gotten back to it yet because other motorcycle projects keep coming up that have filled my spare time.

#439563 - 06/10/12 6:29 pm Re: A65 Head Flow - Match The Ports [Re: Gary E]  
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Gary E Offline
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Medford, Oregon
Aw, I understand, as the list of things to do here is also long. Too many things not enough time. Have been "trying" to continue with the rebuilding of the Spitfire engine, so inteneded to get a jump on what I will do with the head, hence the flow considerations. Thanks for contributing the info.


1967 BSA Wasp
1967 BSA Hornet (West Coast Model)
1967 BSA Hornet (East Coast Model)
1968 BSA Firebird Scrambler
1968 BSA Spitfire Mark IV

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