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Discussion in 'Airheads' started by Lornce, Jan 15, 2008.
More pics!!! show us your lifters!
Sorry 'Chew, I never thought to photograph the lifters. Nothing special about them; they were stock.
Though I did coat them liberally with oil before I put them back in the case.
How did you achieve the 12:1 CR? Is it dual plugged? I'm curious about the specifics it took to make it run well. It was running the stock cam previously with the 1050 pistons, large valve heads and 40mm Bings? Any mods done to the advance and timing?
12:1 (185psi measured cold) is achieved by using a pair of '77 RS heads modded to suit the 1050 Venolias. Specifically - the Venolia's flat periphery. Think squish band as it was meant to be. (BMW's famous "squish band" top ends of the '77 S's and RS's are over 0.100" deep. ie: nice idea but practically useless).
Heads are machined for dual plugs, but I don't use them. I've had problems in the past with reliability from Dyna and Accel coils, so am a little shy about running dual plugs. I'm convinced it would run better at the bottom end with dual plugs, but the squish band is so effective it runs fine with only single plugs. Pre-ignition is not an issue, though I do need to run cooler plugs over the stock set up.
Previously, with the stock cam, modded heads and 1050 Venolias it ran great with 40mm carbs modded slightly richer - increases in torque and power were dramatic. Made off-road and trail riding especially easy with it's huge gains in low end torque/power. It'll idle up walls. Also, fuel efficiency increased to a fairly consistent 55mpg (imperial) which is better than the best of 44mpg it achieved in stock form.
Ignition system is completely stock except for a Harley Davidson coil I fitted in a pinch to replace a failed Bosch piece. It's been there 40k kms now and works without any discernable issues. Though "in theory" it's not idealy suited to the system.
muter mutter mutter...
If I hear you right, the only changes were the 1050 pistons/barrels and the heads were modified?
Were the heads shaved to achieve the 12:1? How were they modified? What specifically was done to create the squish band?
I've got a 77R100S that supposedly has a 1050 kit (so I was told by the PO, though there are no receipts to prove it) and it's been dual plugged. Supposedly it's got higher compression too. With mods to the advance I've managed to get it running pretty good with minor pinging under hard accelleration but it would be better to eliminate it altogether.
It seems that you have the answer!
You make a lot of demands for a guy who isn't sure what's in his own motor.
Tell you what, send your heads to:
"Stay Tuned" Systems Inc.
Mount Hope, ON
And tell him you want the full enchilada and that you're using Venolia 1050cc pistons. But make sure you are, first.
It wouldn't be cool to go broadcasting someone else hard won tuning secrets all over the internet, but if you know anything about the shape of '77 heads and Venolia pistons, and you can do rudimentary math, it won't take long to figure out how the 12:1cr is derived.
Don's port work is part of the equation, too.
Hint: stock heads with 1050cc Venolia's generate about 9:1cr and have almost no useful squish effect.
Changed the output flange seal in the final drive this evening and when I tried refitting the final drive to the swingarm/shaft combo in the frame I nearly went mad.
In the end I removed the swingarm/shaft combo from the frame and held the final drive in a vice with the pinion gear spline facing upwards. In this position it was easier to keep the u-joint straight enough to get the splines mated.
With the para-lever pivots refitted into new bearings the whole shmere was put back into the frame and the swingarm adjusted for centre and the pivot bearings for preload.
With the rear wheel attached and the driveshaft held in place by the rear brake I torqued up the trans output flange bolts on the driveshaft with lock-tite and without lock washers.
As soon as the new exhaust gaskets arrive (hopefully Saturday) it'll finally be ready to roll out for a break-in run. Aiming for Sunday afternoon.
Here's hoping. Looking forward to riding that bike again.
This pic has nothing to do with this stage but I like the perspective.
maybe i'll see you in belfountain tomorrow afternoon
The Monster liiiivves.
The motor's strong and smooth... but now the clutch is a weak link.
Ding ding ding!
Wheelie pics are needed.
(it'll help you kill off that clutch!)
When I can find someone to take them I'll post them toot sweet.
There's lots to photograph. :wink
p.s. the clutch "self healed" once it got hot and bothered enough to burn off the solvent used to clean the mud off the pressure plates...
What happened to the rest of this? I'm so jealous of the bike.
So, I guess I'm trying to cure that by getting some pictures to drool on.
Ya Lornce.. can you please keep posting pic's of this rebuild so I can live vicariously through you .... that way my hands keep clean and my wallet fatter. Looks good so far.
Never occured to me to photograph the bike once it was together. Looked pretty much the same on the outside as it did before I fixed the inside.
Here's a link to a thread about the Ontario Adventure Riders recent involvement at the Toronto bike show that features a pic of the bike.
It's running great, too, btw.
Heh. This brings back memories.
You've a beautiful bike. Huge, loud, and terrifying, I bet.
Thanks, it's beautiful to me. Never more so than when it's covered in dirt and grime.
It's actually nice and quiet with the stock exhaust still fitted. Partly I like the quiet and partly I've never quite been able to stumble upon a nice cheap used Supertrapp.
Not at all terrifying. Just a comfy all-rounder with a bit of healthy throttle response.
Airheads ruin you for lesser bikes.
Here it is at the carwash after a recent ride:
Some of the riding company it keeps:
Buddy with KTM 950SE: "When are you gonna get a new bike?"
Me: "When KTM's start passing me."
'74 R90/6 For Sale