Tyre pressures?

['It must be a .....']

You can fee slightl swinging arm play at the pivot end by having a finger touching the swinging arm and frame then pushing the chain up or down with the rear wheel off the ground.

[mbmm350s]

The 250 is different swingarm arrangement to 350 and 500 and is also different to 125. They are all similar in having the solid bushes. The bushes are a top hat shape unlike 350 bushes and so the outer face of the bush is a bearing surface to the frame. The spindle is installed from the left which annoyingly means the left side exhaust needs to be removed. The spindle is not threaded on the left but rather rests in a cone shaped cup in the frame, the right hand side is threaded into the frame, the spindle is tightened until nearly all the end float is eliminated, the right hand side is just a locknut.
If the spindle is overtightened the right side frame plate can be swaged outward.
No Morini manual describes the detail of the 250 2C swinging arm but its pretty simple.
Both our 250s have detectable play in the bushes and need rectifying but neither bike is unstable, new bushes are available but spindles are hard to find in new condition.
One thing if you are used to riding modern bikes with fat tyres of low profile then the switch to 100% profile skinny old fashioned tyres can be a little disconcerting for some.
Mark

[Parker3865]

Just returned from a week away and thought I would measure my tyre pressures.
Rear; 26ish psi
Front 20ish psi
I think I checked them a couple of rides ago. Maybe just over a month ago.

So my conclusions are:
1) Check tyre pressures every ride!
2)Run at with pillion pressures (rear maybe up to 38psi) See picture of chart I made to convert from ATM and BAR to psi.

tyre pressure coversions.PNG (20.54 KiB) Viewed 665 times

3) Don't use ContiGo tyres again!! Easy as they will not be making them, but current tyres will probably outlast me given the annual mileage I am likely to do.

[BarryCambs]

I was talking about this with Mark at the AGM yesterday. I've always found the handling and straight line stability on my to be fantastic. We had a look in the car park and it's got Metzeler ME22 on it. I think I went with these as they was some sort of consensus on the forum when I got it. Having told Mark I wouldn't have deviated from the standard fitting, it turns out it's got 2.75 on the front, but a 3.25 on the back. I've no idea why, but maybe it had a 3.25 on it when I got it. It's not at all sensitive to tyre pressures. I use 29 from and 32 rear.

We did wonder if there could be something else wrong, especially given you started from a from a pile of parts? Does it have the correct fork springs, or has someone substituted some from another bike over the years, sort of things??

I've just measured a couple of things on mine, with the help of a young child and me holding the bike as upright as possible, so I'm not saying they are millimetre perfect!

The rear shocks are Hagon and centre to centre (no load) look to be 310mm. with it off the stand, floor to centre of the top shock mount - 620mm. With me (93kg) sat on it, it only drops to 600mm.

From the floor to the back corner of the fork yoke is 935mm.

I think you said you're in Brentford or Braintree, so if you want to meet half way or something, you're more than welcome to try mine or compare fork stiffness etc.

Barry

[Parker3865]

Barry, many thanks for your thoughts and measurements .My forks have the same dimensions as yours. My shocks are 320mm, I am not sure 10mm will make that much difference. The forks and shocks have 5w oil in them. I think the forks are softish, but feel that is spring rate not damping.

In the meantime I checked my rear pressure again today and it was down to 33psi, from 39psi on Saturday. I found I could tighten the valve body quite a bit so am now wondering if I have had a slight leak through the valve, leading to lower pressure. The wobbly feeling is more rear tyre low pressure than fork angle being wrong.

I am in Brentwood, so not far from Cambridge. It would be nice to meet up sometime and compare notes

[mbmm350s]

Hi Richard
Original Sebac shocks 310mm between centres, replacement Marzocchi also 310mm.

10mm wouldn't make much difference would it, especially as shocks are not vertical?

Personally i would go for a medium grade fork oil which is 10W but this is really down to personal choice on how you like the feel.

We have found on 350s all sorts of preload spacers worth checking you have sufficient front fork preload.
I would want the spacer to be a little proud or flush with the top of the tube, front unloaded, so you have to push the nut to engage the thread. I disassembled the 1983 250 to help check. The other 1980 2C has ACE bars and would require more diassembly.
The standard length on the 83 250 is 60mm. Oddly the spacer is not shown in the parts book. The spring is 455mm. The spacer is 3mm proud of top of tube.
If 350s are anything to go by all sorts of spring lengths and spacers could be present.

Cheers Mark

[Parker3865]

Mark, thanks for all of the useful info. I may try 10w oil. I have bought some forks from Arthur, so I can see if I can get mine better! The damper rods are very corroded and one of the forks still has a little more play than I would ideally like. I can measure my springs and compare.

Occam's razor? The simplest things...
So:
1) As mentioned I have tightened up the valve in the valve body and the tyre maintains pressure for at least a week, not sure it was before.
2) I feel so stupid, I checked the pressures with a different gauge and found my, new this year, tyre pump gauge is overeading. So 30psi on the gauge is nearer 20psi on other gauges.
Ran at 28psi front and 38psi rear today for a fair run at different speeds and felt a lot better. The 'a bit weavy' seems to be gone, at last!

[norbert]

You are talking here about the 250V if I am right?

But surely a lot of 350 driver are following the theme as well.
Till now I´ve only ridden 350 chasis. As far as I know normaly they all came with 300mm rear shocks. I´ve put 315 mm Konis in a 74 Strada frame and for me it is ok. Some people don´t like them for beeing a bit hard To me they are fine like the 300 Ikons I have since 20 years in another 350 K frame. Travelling with clip ons in a bit sporty way (not racing!)

I´ve allways used SAE 15 fork oil in the Marzocchi forks.
Till I`ve mounted a fork with Paioli dampers from a 74 Strada (using the 230 doblesimplex from a Benelli Tornado). That was much harder than I was used to. I had to change to SAE 10 an even a bit less. The dampers are quite diferent! Since a couple of years I wear the cartridge dampers from Sören in that fork (I guess the Idea is from Paul Compton, if I´m right) with SAE 3 (!)
To me it seems that the Paioli dampers in the fork of the drum brake area need a more fluid oil than the Marzocchi dampers of the disc models to feel the same. I maybe wrong, but that´s my experience.

For many years I allways put 200 ccm (ofSAE 15 as said) in each leg. I reduced it to about 180 ccm to get it a bit smoother and raise the air damping efect.
But all this about how you want your rear shocks and the fork is a very personal, individual theme as Mark says like handlebars and a harder seat or a sofa

[BarryCambs]

Don't feel stupid - it took me a while to realise my beautiful and expensive new pump was reading 10psi low.

[MickeyMoto]

Mark, thanks for all of the useful info. I may try 10w oil. I have bought some forks from Arthur, so I can see if I can get mine better! The damper rods are very corroded and one of the forks still has a little more play than I would ideally like. I can measure my springs and compare.

Occam's razor? The simplest things...
So:
1) As mentioned I have tightened up the valve in the valve body and the tyre maintains pressure for at least a week, not sure it was before.
2) I feel so stupid, I checked the pressures with a different gauge and found my, new this year, tyre pump gauge is overeading. So 30psi on the gauge is nearer 20psi on other gauges.
Ran at 28psi front and 38psi rear today for a fair run at different speeds and felt a lot better. The 'a bit weavy' seems to be gone, at last!

I was once told there should be a 3 to 4 psi difference front to back. Not sure if anybody has a clue about it?

I use 32/36 on my 350, but then how do I know my gauge is correct?