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Old 04-22-2013, 10:12 AM   #1
benthic OP
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MOAR OOOMPH! (R80/7 to dual plugged 1000)

On Friday I fired off a check for the following:

-Squish band Heads, Pistons and Rods from 1977 R100S, Heads are dual-plugged; magnesium valve spring retainers. Pistons have lightweight wristpins, rods and pistons balanced. Pistons have Nikasil compatible rings.
-Pair of nearly new Nikasil cylinders- about 20,000 miles on them.
-Pair of 40mm Bing carbs

In terms of condition, there are some dings on the cooling fins, nothing broke or noticeably bent. The pistons are quite functional; if not as pretty as they once were. Exhaust port (38mm) threads are old; not damaged. Valves are good; some slight "tuliping" in the left intake; but the valves are smooth and not loose in the guides; "lap them and use them". Might want to have the rods made more roundy and fit new bearing shells and bushings too. When live on bike the compression was consistently 150 Right/147 Left.


Over the weekend I did some reading:) and I have questions do you have answers?

If I understand correctly, what I NEED is new coils, new plug wires, and a points booster. Do I have this right? I read something that implied I might need 2 boosters is this right? The bike currently has a stock 1978 R80/7 engine (points).

Might want to have the rods made more roundy Im not sure what this means

Also, I've read mention about a new final drive, but i don't understand why it would matter, can anyone give me a simple explanation of why I'd want to do that, and why it's ok not to?

It seems Accel and Dyna are the most frequently reference coils any real difference between them?

In addition to what I NEED, any upgrades changes worth looking into while Im at it? Im going to wait to order anything until I have the parts in my hot little hands, and I expect that to happen later this week/early next week with any luck:)

Thanks all!
Spencer
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1978 BMW R80/7
"all we need is time and courage." - Renner
"A lightened flywheel on your bike is like me getting into Spandex and putting on track shoes to walk the dog." - M
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Old 04-22-2013, 10:42 AM   #2
Airhead Wrangler
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Can't speak to the dual plugging part, but as far as the final drive is concerned, the R80 final drive is a bit low of gear ratio for a 1000cc top end. You'll have monstrous torque being put to the ground, 1st gear roll-on wheelies might be possible, and your 0-60 acceleration will be pretty impressive (for an airhead), but cruising at 70 mph you'll be spinning much higher revs than necessary and won't get the greatest gas mileage.
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Old 04-22-2013, 11:22 AM   #3
chasbmw
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The tricky bit with dual plugging is getting the right ignition timing curve, this means making some changes to the original advance and retard unit so that ignition timing is stock at start up, but retarded 4 degrees at a full advance @approx 4000 revs.

Various ways to do this, search the web or use an electronic ignition unit with a suitable ignition curve.
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Old 04-22-2013, 12:07 PM   #4
benthic OP
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Quote:
Originally Posted by Airhead Wrangler View Post
Can't speak to the dual plugging part, but as far as the final drive is concerned, the R80 final drive is a bit low of gear ratio for a 1000cc top end. You'll have monstrous torque being put to the ground, 1st gear roll-on wheelies might be possible, and your 0-60 acceleration will be pretty impressive (for an airhead), but cruising at 70 mph you'll be spinning much higher revs than necessary and won't get the greatest gas mileage.
I still don't understand why it will be reving higher - why wouldn't it be spinning at the same speed?

Quote:
Originally Posted by chasbmw View Post
The tricky bit with dual plugging is getting the right ignition timing curve, this means making some changes to the original advance and retard unit so that ignition timing is stock at start up, but retarded 4 degrees at a full advance @approx 4000 revs.

Various ways to do this, search the web or use an electronic ignition unit with a suitable ignition curve.
From what I've read, I should be able to do this with my points, worst case having to file additional adjustment into the existing holes(?).

thanks!
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1978 BMW R80/7
"all we need is time and courage." - Renner
"A lightened flywheel on your bike is like me getting into Spandex and putting on track shoes to walk the dog." - M
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Old 04-22-2013, 01:25 PM   #5
Airhead Wrangler
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Quote:
Originally Posted by benthic View Post
I still don't understand why it will be reving higher - why wouldn't it be spinning at the same speed?
Yes, it will still be spinning the same number of revs for a given speed, but highER than necessary for 1000cc top end. It will be spinning higher revs than stock R100 models and you won't gain any top speed. You could give it a higher final drive ratio because you now have a bit more HP to push those taller gears. Or you can just accept worse gas mileage and enjoy a zippier bike around town. Either way.
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R80ST Gets The HPN Treatment
Seattle to TDF on an airhead

Current rides: HPN #834, '93 R100GSPD "red rocket", '73 R75/5 Toaster mongrel, '80 Ducati Pantah 500SL, '92 DR350, '67 Honda SS50, '80 Honda Chaly.
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Old 04-22-2013, 01:32 PM   #6
Hookalatch
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Quote:
Originally Posted by benthic View Post
I still don't understand why it will be reving higher - why wouldn't it be spinning at the same speed?



From what I've read, I should be able to do this with my points, worst case having to file additional adjustment into the existing holes(?).

thanks!
He didn't say you would be reving higher, just higher than necessary. The engine will be turning the same rpm as before but the additional power you engine produces means it could do it at lower rpm's (if you wanted to change gearing). The 1000cc engine will likely vibrate more at the same rpm but that isn't necessarily a given depending on balance and tune.

I am doing a similar swap on my R80 engine and see the lower gearing as at least a theoretical advantage for my riding. I am more interested in the bike being quick than fast. However, I haven't had it on the road yet and may not be happy but I think I will. Anyway I am mentally prepared to change final drives and the speedometer if it turns out I don't like it geared that way.

Chuck
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Old 04-22-2013, 01:46 PM   #7
benthic OP
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AW, Hookalatch - i think i understand. It will be reving the same as the stock 80, but is producing enough power that it doesn't HAVE to rev that high. and it won't gain top speed because my final drive is now the limiting factor? I think i'm ok with that. I haven't found the stock R80 to be to slow;) I will be curious about the gas milage, if the drop is significant. I wonder if the dual plug will mitigate that at all(?).


Quote:
Originally Posted by Hookalatch View Post
...The 1000cc engine will likely vibrate more at the same rpm but that isn't necessarily a given depending on balance and tune...
From what I understand, the lightened wristpins are supposed to help address the increased vibration.

Thanks guys!
Spencer
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1978 BMW R80/7
"all we need is time and courage." - Renner
"A lightened flywheel on your bike is like me getting into Spandex and putting on track shoes to walk the dog." - M
www.blindfishz.com
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Old 04-22-2013, 01:56 PM   #8
Airhead Wrangler
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Quote:
Originally Posted by benthic View Post
I will be curious about the gas milage, if the drop is significant. I wonder if the dual plug will mitigate that at all(?)
Depends on your compression ratio. If you go with stock 9.5:1 (stock for '77) then you might actually not lose much in gas mileage. Dual plugging will just help you run crappier gas. Without dual plugging, 9.5:1 probably should use premium depending on your climate.
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R80ST Gets The HPN Treatment
Seattle to TDF on an airhead

Current rides: HPN #834, '93 R100GSPD "red rocket", '73 R75/5 Toaster mongrel, '80 Ducati Pantah 500SL, '92 DR350, '67 Honda SS50, '80 Honda Chaly.
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Old 04-22-2013, 02:25 PM   #9
Rob Farmer
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Don't forget the rs airbox. The one with the perforated back.

You won't get the ignition right with your points. The twin plugging works against you at higher rpm. Boyer make an ignition with a twin plug curve.

For my money I'd stay single plug. Keep the 32mm carbs. Port the heads and fit high comp pistons. Rs airbox and rs bevel box. I have a 78 100/7 with this spec and it runs beautifully.

If you stay with the 80 bevel box the bike will feel like it's revving its nuts off, it needs some load to pull against

Rob Farmer screwed with this post 04-22-2013 at 02:36 PM
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Old 04-23-2013, 10:31 AM   #10
benthic OP
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Quote:
Originally Posted by Rob Farmer View Post
Don't forget the rs airbox. The one with the perforated back.

You won't get the ignition right with your points. The twin plugging works against you at higher rpm. Boyer make an ignition with a twin plug curve.

For my money I'd stay single plug. Keep the 32mm carbs. Port the heads and fit high comp pistons. Rs airbox and rs bevel box. I have a 78 100/7 with this spec and it runs beautifully.

If you stay with the 80 bevel box the bike will feel like it's revving its nuts off, it needs some load to pull against
I figured I could drill out my current airbox, but I'm keeping my eyes open for an already perf'd clamshell (although, I've heard that the later style snorkel box is better)

I'm looking into a electronic ignition, but am not sold yet...

I can't stay with the 32mm carbs because i'm getting the big intake valve heads.

The set of parts i'm getting has a Compression ratio of 9.5:1; stock for 1977 R100S.

I guess I'm still confused about the final drive - if it will be reving the same (as discussed above) as the stock engine, why will it feel like it is "revving its nuts off"? Because of the potential for increased vibration?

Thanks!
Spencer
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1978 BMW R80/7
"all we need is time and courage." - Renner
"A lightened flywheel on your bike is like me getting into Spandex and putting on track shoes to walk the dog." - M
www.blindfishz.com
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Old 04-23-2013, 11:00 AM   #11
Lornce
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Quote:
Originally Posted by benthic View Post
I guess I'm still confused about the final drive - if it will be reving the same (as discussed above) as the stock engine, why will it feel like it is "revving its nuts off"? Because of the potential for increased vibration?

Thanks!
Spencer
'77 R100S top end parts mated with Nik barrels is a nice find.

Re. Gearing: The R80 gears (3.36:1 ) are too short to make practical use of the healthy torque and power produced by the R100S top end. With that top end mated to 33/11 or 32/11 gears (ie: lower operating revs) you'd exceed the performance of your R80/7 and likely exceed it's fuel economy, too. Fuel economy of the R100S motor with the R80 gears will be quite poor and the bike will feel unnecessarily frenetic/busy while riding at higher speeds.

I'd be looking for a 33/11 (3.00:1) or 32/11 (2.91:1) final drive if it were me.

But that's just my preference.

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Old 04-23-2013, 02:08 PM   #12
Rob Farmer
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If the heads are 77 then the exhaust ports will be 40mm so your going to need 40mm headers to suit along with matching silencers.
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Old 04-23-2013, 02:15 PM   #13
benthic OP
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Quote:
Originally Posted by Lornce View Post
'77 R100S top end parts mated with Nik barrels is a nice find.

Re. Gearing: The R80 gears (3.36:1 ) are too short to make practical use of the healthy torque and power produced by the R100S top end. With that top end mated to 33/11 or 32/11 gears (ie: lower operating revs) you'd exceed the performance of your R80/7 and likely exceed it's fuel economy, too. Fuel economy of the R100S motor with the R80 gears will be quite poor and the bike will feel unnecessarily frenetic/busy while riding at higher speeds.

I'd be looking for a 33/11 (3.00:1) or 32/11 (2.91:1) final drive if it were me.

But that's just my preference.

I just got some great news that a good friend of mine can probably lend me a FD from a 100/7 so i might be able to try before I buy one (and I located one locally that's for sale). I think I'm going to have to see for myself how the bike runs at speed with the new parts...

Quote:
Originally Posted by Rob Farmer View Post
If the heads are 77 then the exhaust ports will be 40mm so your going to need 40mm headers to suit along with matching silencers.
According to the seller the exhaust ports are 38mm, so I shouldn't have a problem there (fingers crossed because that would suck since my headers are shiny and new)
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1978 BMW R80/7
"all we need is time and courage." - Renner
"A lightened flywheel on your bike is like me getting into Spandex and putting on track shoes to walk the dog." - M
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Old 04-23-2013, 05:05 PM   #14
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Quote:
Originally Posted by Rob Farmer View Post
If the heads are 77 then the exhaust ports will be 40mm so your going to need 40mm headers to suit along with matching silencers.

There were no '77 R100S's sold in North America with 40mm exhaust ports.

The first '77 RS's to arrive had 40mm ports, but not even all the '77 RS's arriving in N. America had 40mm exhaust ports.

fwiw.

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Old 04-23-2013, 08:01 PM   #15
Beemerboff
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My 1000cc twin plugged R80 G/S DOES 21 KM/L on standard gearing, 19 KM/L with a 5% higher fifth gear.

My bike is smooth and well tuned so I cant tell the difference in revs, but there is a decent sort of difference when you open the throttle.

As Rob has said , Boyer sell a Micropower dual plug system which includes coils, plug leads and caps, and costs less than a pair of Dyno coils and a booster.

The curve is just about perfect, and as the electronic system fires at exactly equal intervals the engine runs smoother too. It only has one curve, the right one, so you are spared the expense of dyno time selecting the best curve from the 22 or so available on some other systems which cost 3 to 4 times the price.

Mine replaced a bodged A/R unit with Dyna coils which the PO has fitted, and the improvement in starting, smoothness and performance is well worth paying at lot extra for, and as it comes in cheaper it seems to me to be a no brainer.

I bought mine from Gremlin Racetech, Motobins have then but I dont think they trade with the US
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