The New And Improved Unofficial R65 Forum V2

Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: mendozeal on August 13, 2011, 05:03:43 PM

Title: installing double crossover headers on a 79?
Post by: mendozeal on August 13, 2011, 05:03:43 PM
again I think the title says it all,
any advice? is it worth it?

also really hoping this 81 corbin I just ordered can be made to fit..
I know the 79 is just a little different but in some funky ways..
Title: Re: installing double crossover headers on a 79?
Post by: Rob Valdez 79 R65 on August 13, 2011, 06:03:45 PM
Did they say what the Corbin seat was installed on, originally?

I know I have seen at least one seat from a Type 247 installed on a Type 248 bike.
Title: Re: installing double crossover headers on a 79?
Post by: mendozeal on August 13, 2011, 07:52:26 PM
Quote
Did they say what the Corbin seat was installed on, originally

it was on a r100 /7
which just lurking on bmw owners of america, I heard this may be the best bet bike.. the ad suggests "but i think it will also fit on 1977-1979 models with the dual sport seat cowling."
but we will see.
Title: Re: installing double crossover headers on a 79?
Post by: Rob Valdez 79 R65 on August 14, 2011, 04:20:28 PM
Quote
Did they say what the Corbin seat was installed on, originally?

I know I have seen at least one seat from a Type 247 installed on a Type 248 bike.
Yes, it is RSMike that has one on his bike!

http://www.bmwr65.org/cgi-bin/yabb2/YaBB.pl?num=1313353555
Title: Re: installing double crossover headers on a 79?
Post by: nhmaf on August 14, 2011, 04:25:10 PM
The /6 seat pans were longer than the /7 bikes', so it would be a better bet that a /7 seat may work than a /6 seat
Title: Re: installing double crossover headers on a 79?
Post by: RSMike on August 14, 2011, 05:13:37 PM
Yes, a /7 seat should fit, I just needed to lower the rear fender very slightly. detail at the link posted by Rob

And yes, I can confirm that no way a /6 seat will fit, too long, my supplier sent me one accidentally before the /7





(modified to "no way" by moderator Rob, for clarity)
Title: Re: installing double crossover headers on a 79?
Post by: tvrla on August 14, 2011, 09:51:19 PM
also really hoping this 81 corbin I just ordered can be made to fit..
I know the 79 is just a little different but in some funky ways..

It might possibly work.

In the late 90s I bought an 83 R100RS with an LS seat installed. It didn't fit the best, but it did work. I wanted the stock seat and tried selling the LS seat with cowl and almost had to give it away. Wish I still had it - it was a nice one.
Title: Re: installing double crossover headers on a 79?
Post by: RSMike on August 15, 2011, 02:25:28 AM
thought the link above was a different one, here is the link to my fitting of the /7 seat:

http://www.bmwr65.org/cgi-bin/yabb2/YaBB.pl?num=1309703763
Title: Re: installing double crossover headers on a 79?
Post by: Semper Gumby on August 15, 2011, 11:24:54 AM
Quote
again I think the title says it all,
any advice? is it worth it? <snip>

Don't know about the seat.

I know the theory about the headers though.  

The front crossover nearest to the cylinders was to improve engine response at low RPM.  The Crossover back near the center stand is for better engine scavenging at high rpms.

Problem is BMW didn't just change the headers between 1979 and 1984.  They changed the airbox assembly, the carbs, they added a pulse injection air system (which we all get ride off).  The whole thing is tuned.  So yes it will go on the bike but can you get it tuned right with your 1979 airbox, filter and carbs?  I think there are enough tools and experience about to make it work OK.  But this is a first as you are in uncharted territory.  You might post up on Boxerworks and see if there is somebody in the much larger airhead world that has experience with doing this.  This may not be a big deal.

So after you put them on go ride it!  Look for flat spots as the motor accelerates and listen for popping sounds as the motor de-accelerates.  If this all works out OK, then just have a look at the plugs to make sure you are not running too hot.

If you sense problems then I recommend two things:  buy the Bing Agency Caberettor manual and get a Colourtune Plug.  Because first we have to know why things are different and how and where to change them and second we have to see what is happening to confirm or feelings about the motor.  Then post up here and tell us what is going on.  (I can hardly wait.)

I recommend the Bing agency manual to every R65 owner regardless of whether he/she is having problems or not.

Good Luck!   8-)
Title: Re: installing double crossover headers on a 79?
Post by: mendozeal on August 19, 2011, 03:20:28 PM
So the headers showed up, got them prepped and painted, and will be installing them as soon as my fin wrench shows up...

Im posting this same post on boxerworks, (with your reply too...) and just ordered the bing manual, and a carb sync kit. well see what happens, I figure just to be "safe" Ill prep and paint the old ones two when I take em off.

I will definitely keep you posted, with pics, and video when its running.
Title: Re: installing double crossover headers on a 79?
Post by: mendozeal on August 19, 2011, 03:57:50 PM
found stuff related to 79's with "double headers"  lurking at http://boxerworks.com waiting for my account to be approved.

My carbs are 64/32/203 & 204 (from a '79)
flat tops type 64-2. slide 911-24, main jet 140, needle jet 2.66, clip position 2

For '81-'84 they were 64/32/335 & 336
r65ls type 64.3, slide 907-1, main jet 138, needle jet 2.64, clip pos. 3

after reading on, I decided to change my jets to the 81 size
(mj138 nj2.64) and will be changing the clip position from 2 to 3.

I also ordered the total carb rebuild kit.
bing reccomends every 20,000 miles, and mines a 79 with 20k. diaphrams still look good but it cannot hurt.
Title: Re: installing double crossover headers on a 79?
Post by: Semper Gumby on August 19, 2011, 09:03:31 PM
Thats a whole lotta stuff to be changing at once.  It helps that someone on Boxerworks has done this before.  I hope it all works out.  Keep us posted.

I'm not going to attempt this myself but I am more than a little bit curious.  The Post 1980 bikes had a lighter flywheel requiring a different tune than the 1980 and 1979 bikes...

Title: Re: installing double crossover headers on a 79?
Post by: Rob Valdez 79 R65 on August 19, 2011, 10:57:09 PM
I rejetted my 203/204 Bings on my '79 to accommodate the larger-valved heads on the '81 R65 engine I put in my bike.

I don't know if the double crossover headers would warrant such a change, but I could easily be wrong.
Title: Re: installing double crossover headers on a 79?
Post by: Barry on August 20, 2011, 04:35:29 AM
I'm not sure you can make sensible jetting comparisons between 79 flat top carbs that have no slide spring and 81 carbs which presumably do have a spring. In other words I don't think putting the 81 jets in a 79 carb will give the same results as they would in an 81 carb.

I once tried the 81 smaller main jet size in my flat tops and the bike would hardly run above 3000 RPM. Mind that was going from a 123 down to a 105. Your change from 140 to 138 is hardly going to be noticeable.

The needle jet change from 2.66 to 2.64 is going to lean you out but will be compensated with a higher needle position.  My guess is you may run a little cold blooded in the low to mid range then it will rev out OK once the slides lift and your working on the tapered section of the needle.

As Gumby said it's an awful lot to change at once. If it was me I'd try fitting the new headers and keep the stock jetting. I bet it runs just fine like that. If not I'd experiment with one jet change or needle position at a time.

I'll be interested to hear how it goes.

Title: Re: installing double crossover headers on a 79?
Post by: mendozeal on August 24, 2011, 01:18:38 AM
had to cut off fin nuts. fun.
double crossovers have a 35mm circumference. the threads on the 79 cyl. head are 32mm.
even the '81 fin nuts wont fit.

game over, going back on ebay.
dang.
thanks for the help guys.
(https://bmwr65.org/smf/proxy.php?request=http%3A%2F%2Fimg.photobucket.com%2Falbums%2Fv307%2Fdreamnightmares%2FP8230148.jpg&hash=261ecbd775a561823ead6c0777b56c5df982435a)
Title: Re: installing double crossover headers on a 79?
Post by: Barry on August 24, 2011, 03:29:45 AM
Quote
double crossovers have a 35mm circumference. the threads on the 79 cyl. head are 32mm.


R45/65's have 35mm dia pipes. Most other airheads are 38mm with some of the 1000's being 40mm.
Title: Re: installing double crossover headers on a 79?
Post by: mendozeal on August 24, 2011, 04:10:21 PM
yeah my measurements were done inside dimensions, and with a plastic ruler. :-?.. sorry haha