Low compression 3 1/2

[Andy_C]

I made it to the Morini stand at the Bristol Bike show yesterday - apologies but I cannot remember who I spoke to, but they were very helpful.

I wanted to get ny hands on a Morini 3 1/2 so that I could try the kickstarter to "feel" the compression.

On mine, you barely notice the compression, I had thought perhaps it was down to the kickstart gearing, but compared to the 3 1/2 on the stand, mine has very little compression.

So what is the issue with mine?

It starts / runs / idle just fine, and it has no problems revving, valve clearances are correct because I checked them, and the bores cant be shot since it does not smoke.

So I am thinking valve timing - when I replaced the belt nothing moved I am certain of that, but the marks did not quite line up, and there was no way you could make them line up. I guess that valve timing could be slightly out and it would still run, but if not opening / closing as they should it could be losing compression or am I wrong ?

Looking forward to seeing what the general opinion is, setting the valve timing does not look to be that difficult, all I need to get is a timing disc.

A

[Andy_C]

An update - bit bored so went out into a cold garage !

Pulled the valve cover off the front cylinder, and set the inlet clearance to 1mm as stated to set / check valve timing.

To get a rough picture of what is going on, I then turned the flywheel first to TDC (The PMS1 mark) - inlet valve was open (well it would be given that it opens 12 degrees before TDC), I then turned the flywheel anti clockwise about 40 degrees or so, and then clockwise to see at what point the inlet valve opened, it is roughly mid way between the PMS1 mark and the A500 mark.

I have been trying to find out what the A500 mark is, and at what angle it is but no joy, if I could find out I could gauge roughly how close the valve timing is.

Other things crossing my mind are that I dont believe that bike had been used much prior to me owning it so could be that the rings are gunged up and might free up after I put some miles on it, secondly perhaps the valves seats are in need of attention, as I say I dont think it can be worn bores as it does not smoke.

Just want to be sure about valve timing before I start riding it in anger in the spring.

****Just noticed the S engine has inlet opening at 28 degrees BTDC and mine has an S engine, but has it got the S cam ? perhaps I should be timing at 28 degrees BTDC****

[3potjohn]

Many years ago I printed a timing disc and stuck it on a CD. Should have used a CD of The Valves.
Using our suitcase weighting hook I get 39lbs or just under 18Kg on the pedal to move it.
Not very standardised is it?

[Andy_C]

Sorry John - I just dont get your reply am I being stupid? don't answer that

[3potjohn]

Not at all, just bored with watching the football and being hemmed in by rain.
I just wondered if I could estimate the effort needed to push the kickstart pedal down and tried a spring balance used for weighing luggage to pull the lever down by way of getting a value.

[Andy_C]

Compared to the 3 1/2 on the MRC stand the compression on mine is minimal - you can just about makeout compression on mine and you can easily turn the flywheel by hand.

The kickstart on the bike on the MRC stand took a lot more effort to push down.

As I say it is a Sport Engine so if it has a Sport cam the timing is 28 degrees as opposed to 12 degrees, so if set for a non sport engine and it does have a sports cam it is going to be 16 degrees out.

Also bored with the seemingly endless rain and winds, Football is a no no for me, Rugby yes, but not Football.

[Martha]

Hi Andy

Which of the three 3 1/2 did you try? Mine, (closest to the Guzzi stand) has an 'unknown' standard of engine build, so may not be representative.

Have you performed a compression check with a tester? There are a standard series of checks that can isolate issues with rings by using a compression tester. If you don't have a tester, as a start, try putting a teaspoonful of oil down the plughole and assess if that gives you more compression. If it does, it is possibly a ring issue. You could also try the same but with each plug out in turn, to see if it is just one cylinder that is problematic.

[Andy_C]

Martha - it was the red one which was parked next to one fitted with an NLM Kickstart.

The tests that you describe are all good ones, but before I do any of those I am going to investigate valve timing, being an S engine I am going to set the valve timing to the S figure and see what happens, if that has no effect, will revert to normal strada value.

Probablhy no way of knowing what cam is fitted without removing and measuing it.

If this has no effect then will look into compression testing.

Both pots are the same compression wise you csan feel it when you kick it over.

[George 350]

Sport cam vs Strada cam
Whilst I've never had the need to do a compression test on either of my Morinis, I do have one of each to compare.
The Strada does require more effort to kick over.
Despite a higher geometric comp ratio, don't forget that the Sport exhaust cam closes significantly later than the Strada, so less 'suck' at kickover speed, and the inlet cam closes way after BDC compared to a Strada, so again at cranking/kickover speed a bigger portion of incoming charge goes back up the inlet port.
Of course, when running, gas dynamics mean this issue is nullified.
In your first post, you say that the marks didn't quite line up. I take it that you are aware that the crank pulley has lots of keyway so that you can 'get it ight'? All the handbooks and manuals detail how to select the correct keyway to use, but a previous owner might not have done so.
Regards,
George

[Steve Brown]

What George says above, and when setting the cam timing the marks are the same for Strada and Sport. So with a degree disc fitted and the clearance at 1mm you will get quite different figures so it should be clear if the timing is out and which type of cam is fitted. (allow a little tolerance for the figures you get versus the quoted figures)
As well as compression testing a cylinder leak test is a good way of finding out what is happening. Or, just take the cylinders off and have a look at what's going on-it doesn't take long.

[BumbleBee]

If its not smoking, its running well and nothing amiss with the timing its probably just the valve seats need lapping.

[Andy_C]

George / Steve - many thanks for your replies.

This afternoon after work I found some time to take a closer look.

I dont have a degree disc so I improvised, what I did was measured the flywheel diameter, multiply by 3.14, and divided the figure by 360 to give me how many mm of circumference = 1 degree and then multipled that by 28 and 12 and put the marks on a piece of tape stuck to the outside of the flywheel so I can see what is hapening at 28 and 12 degrees BTDC - hopefully you follow my reasoning which I think is right.

So if my calculations are correct I could see that the inlet valve was already open at 12 degrees, and at the 28 degree mark BTDC, there was still clearance between the rocker arm and the valve - so the timing was out.

I managed to adjust the belt so that at the 28 degree mark, the 1mm clearance between the rocker and valve stem was zero - or at least as close as I could get it. Think the workshop manual gives you a tolerance of +/- 3 degrees.

So it is now set for a Sport cam, as it was it was neither 12 degrees or 28 as far as I could ascertain.

I double checked it all before tightening up the flywheel, I also double checked valve clearances at the PMS1 and PMS2 marks.

I know about the vernier adjustment of the pulley on the crank, but it looks like it might be rusted in place - any tips for getting a rusted one off if I ever need to ? Cant really see any way other than carefully cut it off with a dremmel or similar.

Compression wise, feels more or less the same although George has given a good reason why the compression feels low when kicking over.

I wont be firing it up for a couple of days as I need a new rocker box gasket, but will give an update when I get it going again.

Bumblebee - Good call, not had a look at the valve seats so might be worth a look - I'll see if the adjustments I have made has doen anything first.

Thanks again.

[Steve Brown]

To get the bottom belt pulley off you need a good 3 leg puller and a thick washer that can be held in place by the circlip on the pulley. It should normally be a tight fit and take some effort to remove. Cutting them off is only needed in really bad cases and a little rust always seems to be there. The whole process is in the manual-have you got one?
The bottom (and top) pullies are both marked by the factory with a small indent. Sometimes it's faint and if it isn't there at all the pulley has probably been replaced, and could likely be out of position. Again the way to get it right is in the manual and not easy to describe on a forum.

[Andy_C]

Steve - that sounds really easy.

I do have a manual, but hold my hands up to never looking up how to remove the pulley.

I have a few decent pullers that should be up to the job if needs be.

Better go and look at the book.

Many thanks again.

[Andy_C]

Steve - that sounds really easy.

I do have a manual, but hold my hands up to never looking up how to remove the pulley.

I have a few decent pullers that should be up to the job if needs be.

Better go and look at the book.

Many thanks again.