What have you done with your bike/s today?

[chaterlea25]

Hi RD,
I was out with some friends on Wednesday   on bikes, it was my first ride out since Covid  and doing my knee in
I borrowed a guzzi for the day
 One of the guys has a 29 Ariel on which he has fitted an electric starter
He fitted a ring gear to the clutch basket and a car starter incorporating a reduction gear behind the gearbox,  it works a treat.

On another forum there is a discussion on fitting a decompresser to a single that originally did not have one
One of the suggestions is to fit the half compression valves used on chainsaws
It might be worth your while checking those out?
At a fiver each on eBay not a lot to lose?
First of all fit them to the sparklpug holes and see if you can kick it over before attacking the heads with a drill 

John

[muskrat]

G'day RD.
I would have thought the lockdown diet of yummies would have helped 
I had to do similar for a mate with a high comp HD.
Good luck.
Cheers

[RDfella]

Thanks for the input, John. I have to say I’ve never come across decompression valves for two strokes for starting purposes, though Villiers engines sometimes had them. Mainly for stopping, I believe.
My project has decompression (by virtue of holding the exhaust valve open) on both cylinders. I have the front connected, mainly because when mag ignited, the rear cyl was the most likely to fire and releasing the front from compression creates less resistance. It has started on the kickstart, but it’s very iffy because ‘getting it over’ is a matter of luck.
Now some Honda four strokes have automatic decompression for starting and it works a treat. My generator has it and pulling the recoil is a breeze. Below is a video of how it operates – bit like the impulse starter on magnetos of the 50’s.
The system is actually quite ingenious and simple – but it would require a complete re-design of the camshaft and driving sprocket. Not impossible, but I’m desperately trying not to create more work. There’s been quite a while now where I’ve just wanted to get it finished.

https://uk.video.search.yahoo.com/search/video?fr=yfp-search-sb&p=honda+decompression+start+mechanism#id=2&vid=eceabe0dec8511cbc80e8b2fcfbe53ad&action=click

[chaterlea25]

Hi RD
The chainsaw units leak off some compression but leave enough to start the engine, then pop closed once the engine starts

John

[orabanda]

The big bore Yamaha's (DT and motocross models) have a decompressor valve which is opened by a cam lobe on the kickstarter shaft, and lifts a poppet valve in the front wall of the barrel.
This allows compression to bleed via a 6mm hole in the barrel, into the exhaust port.

Some of the early 360's also had a decompression lever on the handlebar. the big two strokes had plenty of compression (and performance).

They are always easy starters.

[RDfella]

My project uses modified Yam 500 SR cyl heads. Both have manual decompressors, but, as we all know, an engine will not start decompressed. We need to lose some compression, not all.
And so, following on from John’s comments, I got to thinking about automatic decompressors but, as the Yam cam sprockets are bolted to the camshafts, creating an automatic decompressor would entail a major redesign as clearly one couldn’t attach a centrifugal actuator working through a hollow camshaft when there’s a bolt in the way. And I’d hate to spend months designing / building a new camshaft assembly only to find the fixed position of the decompressor was wrong. Apart from one good video, a few poor pictures and some rambling patent applications, I can find very little on the internet about 4str automatic decompressors.
But I have an idea: The heads have manual decompressors, consisting of a rotating spindle pushing down on the exhaust rocker. Upstairs, there is an alloy cup sandwiched between the head and cam cover with a tiny window in it. Its purpose is to see the peg mounted on the cam sprocket by afore-mentioned bolt as a means of identifying the best kickstarting position. Except you can’t see the damned thing because it’s dark in there.

BUT, it seems to me it would be fairly simple to convert that window / peg into a contact breaker. Which in turn could switch a solenoid operating the decompressor lever. An advantage would be that the cup can be rotated to time the decompressor for best results.
One would just need a handlebar-mounted switch to energise the system for starting.
Could be a lot easier that trying to design a starter system where I’d have to contend with 90* change of direction and associated overhang between drive and crankshaft.

What I’m thinking of is a system whereby compression is released until, say, 30* before TDC. That would have the effect of at least halving the volume in the cylinder to be compressed, effectively making that cylinder temporarily 250cc and lower CR. 
Relying on an open valve to release compression over the whole cycle would require ensuring a balance is achieved where enough gas escaped to make turning the engine over easier, without so much that it won’t fire. That would seem a bit of a challenge, as even how fast one kicked it over would make a huge difference. 

[muskrat]

G'day RD.
Which cylinder has the least duration to firing from the other? I would have thought that by decomping that cylinder there would be enough inertia from the kicker to fire the other. Your V won't quite have the same amount of crank revolution as an XT/SR. Using the manual decomp to get it just over TDC then the boot gives the 4 strokes needed. If you only decomp to 30 BTDC you are still kicking against compression and not carrying enough inertia to fire the second cylinder.
Cheers

Richard, I had a DT360 in the 80's, was easy with the decomp but dangerous without, just like the XT500

[orabanda]

Musky,
I still have the DT's (but I don't drink!).

Faster than an A10, pulls more wheelies, but about a quarter of the range!

Richard

[RDfella]

Musky – the rear cyl. As for decompressors, I only have the front cyl connected. Reason for that was when it was on magneto the rear cylinder gets a better spark that the front and is therefore more likely to ‘strike a light’. Consequently, I decompressed the one lest likely to fire in order to make kicking easier. As soon as it was running on the rear, the decomp lever was released for it to come onto two cyls.
When I built my other twin, I deliberately kept the CR lowish for easier starting, and it is no problem at all (800cc @ 7:1). This one is 1,000cc @ 9:1 and I have to do something about it as without rollers it’s basically unstartable.
I’ve tried the machinations associated with other bikes – getting it to TDC then ¾ of a turn or whatever before kicking it (that’s why the Yam XT has this window I referred to, so you can find the best crank position to kick at. If only you could see through it to achieve that! Good idea that doesn’t work, otherwise I’d try it. 
I gave up on all that and reverted to decompressing the front, bringing the rear up to compression and then kicking, keeping the front decompressed until running on the rear (on the rare occassions it actually kicked over). On the rollers I don’t touch the decomp and just feed it in on the clutch.

I must do some more research on automatic decompressors. Looking at the general design, they appear timed. Which makes sense to me, because bleeding gases off over TDC seems to me likely to inhibit starting as, for example, we find with badly seating valves. I’m thinking partial decompression, where it starts much later up the bore so one is compressing 200 or 250cc instead of 500.

[Worty]

Lovely bikes Orabanda, fancy one myself

[RDfella]

Got pizzed off trying to get the recently-converted-to 12v tractor to charge, so did some investigation of automatic decompressors. Put the 8hp Honda generator on the cycle lift and did a cursory check of valve timings / crank position. I found the exhaust valve starts to open a 2nd time just before the inlet closes and closes again around 45* BTDC, thereby reducing the amount of charge to be compressed. Sufficient to fire the charge whilst at the same time substantially reducing the effort required to spin it over (recoil start).

[beezermacc]

Our club went on its first official run of the year. We did 115 miles around Derbyshire and Staffordshire. The scenery was absolutely stunning.

[Worty]

Derbys and Staffs are my stomping grounds Beezermacc - lovely countryside.

[Greybeard]

Derbys and Staffs are my stomping grounds Beezermacc - lovely countryside.

I love the BSAOC weekends in those areas.

[Butch (cb)]

Rode up to Dunfermline for the week last week. A little over 400 miles each way and a (Guzzi) Club member took me for a 300 mile scoot around the Cairngorms on the Tuesday. I was on Blue my T3. Did just shy of 1200 miles all in and she ran peachy. This despite being slung down the road by another, and my having to make a few running repairs before the return. 

Ordered a new rear tyre for my SP, seemed a lot of money. I'll be fitting that some time.

Also ordered a whole bunch of bits ready to service my pal's Serow 225. That will include wheel bearings front and back and a new chain and sprockets.