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#891712 09/25/22 12:15 pm
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Hi mates,

I recently bought this DBD34, and it is a bit different from my other steeds (pre unit triumphs, Commando, sq4)

[Linked Image from i.ibb.co]
[Linked Image from i.ibb.co]
[Linked Image from i.ibb.co]

I have a few questions regarding it as it has been sitting for quite a long time :
- handling is a bit poor, I think rear Shocks are shot, what are the best options ?
- I was not impressed by the acceleration, perhaps am I too shy on the revs, is reaching 7000 rpm a must for a decent power supply ?
- kickstarter is pita, fooling the ankle if not tiptoeing , is that normal ?


Regards !

Xavier

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Taking claimed values at face value, a Commando weighs 190 kg and has 58 hp. A Gold star weighs 160 kg and has 40 hp. If a 75 kg rider is on both bikes, the Commando has 4.6 kg/hp, while the Gold Star has 5.9 kg/hp. That gives the Commando an almost 30% advantage in acceleration, which is more than enough for the difference to be felt by the rider. Hence, you should avoid drag racing people who are riding Commandos. However, the lighter Gold Star is easier to throw around so you should do quite well racing Commandos in the Alps.

I share your dislike of the forward-leaning kick starter. I find it much more awkward to start with it than with the "normal" rear-leaning kick starter on my Catalina. Although you could swap for a "normal" quadrant to make starting more comfortable, that would be a bad choice because it would have the lever constantly pressing against the inside of your leg while riding. I'm afraid you'll just have to learn to live with it.

As for handling, the correct volume of the correct viscosity oil in the forks certainly is a significant factor, so that's well worth checking before spending money on new Shocks. I put Hagons on the rear of my Catalina, but only because I wanted Shocks that looked original. I don't push the Gold Stars hard enough to benefit from other Shocks, even if they were much better.

nb. I originally wrote Ikons for reasons I can't explain, but I have original-type Hagons (not gas)

Last edited by Magnetoman; 09/25/22 10:01 pm. Reason: nb.
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Looks to be a nice machine with all of the correct bits in the right places

Usual things to address if a Gold Star is not handling well:

Tyre pressures correct
Wheels aligned properly
Forks not twisted, swinging arm bushes not shot?
Correct oil type and level in the forks
Rear shock absorbers adjusted for your weight and distribution
Tyres look to be ok (Avon Roadriders?) I quite like those

Presume you have checked and adjusted all of these things to be just so?

I do like the Hagon gas Shocks and have used them since they came out on various machines, you can get stainless bottom covers for them too.

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Originally Posted by Xavier Devars
Hi mates,.....I recently bought this DBD34, ..........
- I was not impressed by the acceleration, perhaps am I too shy on the revs, is reaching 7000 rpm a must for a decent power supply ?....
Hi and welcome to the exclusive, rarefied, exalted community of GS owners. (Did I lay it on thick enough?)

Power characteristics will vary greatly with camshaft choice. If for example road race cams are fitted, idle will be unreliable and low end will be weak but it will pull strongly from 4500 up to 7000 with a really gratifying surge as it comes on the cam. You will know it when it comes on song.

If it has trials cams in it (kind of unlikely but you never know with a restored bike.) it will run more like a stock B33. Solid idle, good low end but not much top end.

More info would help to really answer your question of what to expect such as:
What cams are fitted
Are valves adjusted properly
Is ignition timing correct
are you using the spark advance correctly

On this last item, the spark lever must be advanced after starting to get full performance. In fact, with modern fuels you will learn to be adjusting it often for best running. I apologise if you already know this but it's an easy oversight for someone new to these bikes. Best of luck as you get to know your new treasure.
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I agree with all the responses above.

My first question would be about the gearing. There are a range of engine sprockets that can fitted that will make a big difference in the acceleration. As well the gearbox ratios will make a difference as you go up through the gears.

I would expect that you have the RRT2 gearset with the close 3rd and 4th gear. If so, most of the acceleration has to be done with the 1st three gears as a shift into 4th only drops the RPM 9%.

Other gearbox ratio sets are more spread out and are easier to live with for normal riding.

Gordo.


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Hi, thanks guys.

I am pretty used to manual timing, and I was a bit surprised when I found out that the engine would only accept full advance as a timing for starting. So today I just gave it a glance, and points gap was no good. So I guess it was a on the too retarded side even with lever in full advance position, but even with that, it was able to reach 5000 rpm while riding. Will re-time tomorrow.

Regarding the handling, I will change the tires (those are shot), re align front wheel, check the swing arm play, change the rear Shocks that are really shot, and refill the leaking front forks.

I have no idea what cams are in, but this beast doesn’t like idling. Oh, and it is RRT2 GBox. I found the clutch to have too little slipping range, a bit kind of ON/OFF .

Regards

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Originally Posted by Xavier Devars
......I was a bit surprised when I found out that the engine would only accept full advance as a timing for starting. So today I just gave it a glance, and points gap was no good. So I guess it was a on the too retarded side even with lever in full advance position, but even with that, it was able to reach 5000 rpm while riding. Will re-time tomorrow..............
Yes, for sure clean and gap the points and then check the timing before digging in deeper. That could be all it needs. Closed up point gap retards the timing.

If, when you check your timing, you find it only 2 or 3 degrees retarded at full advance, increasing the point gap by 2 or 3 thousandths of an inch more than the recommended .012" will get you closer to correct and if later you find the engine does not like that timing because of lower quality modern fuel, you can change it back more easily. (Or, just use the spark lever.)

Originally Posted by Xavier Devars
................I have no idea what cams are in, but this beast doesn’t like idling. Oh, and it is RRT2 GBox..............
It's probably got the road race cams in it.....

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It's well worth checking the current timing before doing anything to adjust it. Luckily, it's easy to do. I have six factory dyno sheets for DBD Clubmans, and all six list 39° BTDC. Ignoring possible effects of modern fuel on timing, because we don't know what those effects are, a ruler down the spark plug hole has sufficient accuracy to determine the timing to better than 1°. Note the height against some fixed point on the head when the engine is at TDC, then drop the piston until the points open (overshoot and return, to eliminate backlash). The following show how much leeway you have in your measurements:

38 __ 11.58 mm
39 __ 12.16 mm
40 __ 12.75 mm

If you find some value other than the above, post the information and I'll let you know where it's currently set.

An inexpensive inductance meter makes setting the timing easier and more accurate than cigarette paper (search for Magnetoman and LCR for more information).

As for your clutch issue, search the Projects forum for Magnetoman and 6-spring clutch to find how a modified socket and torque wrench are used to get the optimum tension on the clutch springs. This alone might solve the on/off behavior you're experiencing.

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Okay, once correctly set, the engine pulls better and it was easy to reach the 7000 rpm mark, well it does not feel really comfortable yet to me as I am not used to and afraid of it blowing like a grenade. A bit of vibrations through the 5000’s, and easily reaching the 70/80 mph.

Step by step…

I’ll check your post about clutch Mag’.thx.

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Originally Posted by Xavier Devars
.......... A bit of vibrations through the 5000’s, and easily reaching the 70/80 mph..........
That''s sounding more like it. Glad to hear your bike is responding like it should.

About vibration, it will vibrate some but I personally find them surprisingly smooth compared to other BSA's. But be sure all the engine and gearbox bolts are good and tight. That will help. Also, the head steady makes a difference but for some reason, some bikes are smoother without it..

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Having reread part of the issue on ignition - your mag should be slack advance so when lever closed and cable is slack you should have full advance and you tighten the cable ie pull lever towards you for retard.
Some early machines and the basic B31/33 models had mags the other way round.

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Yes, that's the same with pre unit triumphs. I have worked on a friend's B31 and learned the lever has the inverted action, which, by the way, is Not really helping if your cable snaps.

Another question :

What value should I expect from a compression test on such an engine ?

Many thanks, Regards

Xavier

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The coarse rule of thumb will be 14.5 (atmospheric pressure in psi) x compression ratio, assuming a cold engine and wide open throttle. So typical CR of 9.5:1 so somewhere between 130 and 140 at best.

It is also more complicated because of the effect of cold cylinder and the true dynamic CR will be lower (aluminium likely 7:1 and iron 6:1 and the heating effect of compressing the air (so x 1.4 but 1.3 is practical value)

So 7 x.1.3 x 14.5 (depending on your altitude/air density) which is approximately same ballpark figure with your pressure meter.

Last edited by Neil1964; 09/29/22 7:04 pm.
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I've found that 9 to 1 whether in a Jag or a Triumph usually shows around 175 psi compression pressure. The heating effect is substantial as explained to us by MM in another thread.

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Xavier: Looking at your photos above it appears that you have cable slack for advance as the cable is on the forward side of the mag.

Slack cable advance was introduced in 1955.

Gordo


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OK.
Just checked the compression on my CB Goldie with scrambles cams in it. 180 lbs on the 5th kick. It cc'd out to 9.1 to 1 when I put it together in 2020 during covid.
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Thx !
I have 150 with electric starter, from cold. And 135 with Kickstarter alone.
So tends to point toward a mid-used engine ?

Oh, can someone share a pic of its fuel line arrangement from fuel bowl to carb please ? (For a GP of course) Mine seems a bit too long and twisty.

Many thanks for all your inputs.

Regards

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What readings do you get with a squirt of light oil or Redex down the bore when you repeat the exercise?

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Hi, left home for a few days. I'll give it a try when back, but it has been running lately, so bore shouldn't be so dry, should it ?

Regards

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Another question comes to my mind : with a RRT2 gearbox, how are you supposed to make a race start ?

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Originally Posted by Xavier Devars
.......I have 150 with electric starter, from cold. And 135 with Kickstarter alone. ............
During your compression check you are holding the throttle wide open of course. If so, the first thing I would do is check the valve clearances. That's your most likely culprit. Sometimes you can actually hear a valve leak hissing if you listen at the carb inlet or the exhaust pipe when holding the kick starter up against compression pressure. (This might take 2 people.)

Do the oil down the plug hole check if the compression is still low after adjusting the valves, AND if you don't hear any hissing, because if you do, you still have a valve problem.. Other big leaks such as head gasket would be rather obvious because it would be chirping at you and oozing black oil from the head joint.

Your bike has an electric starter? What luxury. How do you like it?

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Yep, throttle wide open. Will have a look at the valves then, seems one of the easiest thing to check on this bike !

Electric starter was not a search criteria for me, but since the bike got it, it is a a bonus. Use is not really practical. First you flip a switch energising its loop, then pull the decompressor lever, push the starter switch, let the crank gain momentum and then release decompressor.

As the bike is starting first kick from cold, I don't use it, but sometimes it helps when hot, as the starting may get trickier.

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Ok, I have a good 155 (10 bar +) after 5 kicks, this after resetting valve gaps which were too tight, and checking decompressor had some play.
Oil in the bore didn’t change a thing.

Are there different compression pistons available ? Can it be that mine is on the lower side ?

Regards

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Originally Posted by Xavier Devars
Are there different compression pistons available ? Can it be that mine is on the lower side ?
It could be that the rings aren't sealing, which easily could be a problem if the bike had sat for a long time. Or, it could be a previous owner installed a low compression piston to deal with modern fuel. If you have a borescope and a small metal ruler to bend into an 'L', the graph I've linked to here can tell you the compression ratio. Even without a borescope and ruler, but with a flashlight, you should be able to tell just by looking at the top of the piston whether the CR is less than 9:1.

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I’ll have a look then, thanks. However, the link to your graph isn’t working.

Is 150/155 psi bad for a cold engine ?

Regards

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