550K3 cylinder compression

[nairb]

Hi, I stopped using my old K3 back in 1995 when it started burning loads of oil and poor performance.   Fast forward some 25 years later and I finally decided to restore the bike.

I pulled the top end off and was surprised to find there was no lip on the bores at all.  The rings and oil scrapers were well tired.  So I thought a very light hone and a new set of rings would be ok.  I also put some paraffin down the valve intakes to check for leaks.  They were still in good(ish) shape.

So it was all resembled and after much effort to get the carbs to stop leaking it finally was ready for the road.   The bike actually starts and runs ok.  It could do with the carbs being setup better but it does rev ok and pulls through the gears.
Unfortunately the speed does not match the engine revs.  So I thought it might be the clutch (42k) miles and purchased a new cllutch kit and cable from DSS.  I fitted these and it made no difference at all.

So next I checked the timing - looks almost spot on.  So finally I checked the compression.......
With COLD cylinders and no oil down bores and all plugs out and throttle fully open I tested each in turn.

I found the pressures to all be about 155-165/cylinder.  I think the manual says they should be 177psi.

So after some 200 miles the engine has improved a little but the engine still needs to rev too hard.  I was expecting about 5200k revs for 60mph.

I have been trying to keep the revs down to start with to run-in the engine after the rebuild.

My question is ...... is 155-165/cylinder too low?? when cold.  I should really try the test with a hot engine I guess.

Other than this issue it seems to run ok.

Ta
Nairb

[robvangulik]

The amount of revs at any speed is mechanically determined and high or low compression has nothing to do with that.

[Seabeowner]

As said compression will make no difference to revs vs speed. The only thing is clutch slip.
With standard final sprocket gearing 17/37 at 5000rpm you should get: 3rd-45mph: 4th-55mph: 5th-63mph.
Different tyres and inaccuracy of gauges will make a difference.

[Bryanj]

Thatcompressionis fine and definately not your problem, is your memory offa bit as they do need to be reved through thegears even up to top of red bad

[nairb]

That compression is fine and definately not your problem, is your memory off a bit as they do need to be reved through the gears even up to top of red bad

Well I thought I might add a bit more now its done 450 miles since its rebuild. I think the above statement "memory off a bit"  is very true.   I have several other bikes. A 500 single, 2x550, a 450 and a xs650.  The 550k3 is the only inline 4 I have.  But I have done some 42k with it in the past (25+ years) so I did know it quite well...... "did" is the word.

So I thought to start with there MUST be some clutch slip or other problem still with the bike.  The engine seemed to be revving far to high.  And little acceleration.
But I kept the revs down to start with to try and "run in" the top end.  And went about the country lanes.  As the miles went by the engine power came up a bit.
The gearing is 17/37 and the engine will pull about 5200k at 60mph.  Assuming the gauges are still semi accurate??.

With 450 miles done the engine is running ok. So it seems that I really had forgotten how much these bikes needed to be revved to get up to speed.  I still try to change up to a sixth gear.  I might try an 18 front sprocket and some stage.
Thanks
Nairb

[Bryanj]

If you do it will not accelerate very well, the overal gearing is very similar to the 500 as although the sprockets are different so is the primary gear ratio.
In the original 500 handbook it says it is not advisable to rev out of the top of the red band! These fours really need buzzing  over 6-7 grand to keep going and are happy cruizing in the same range

[nairb]

A final comment.... the k3 has now done some 750 miles since being brought back to life.  In the last 15 or so years I have mainly rode a bunch of Suzuki triples, a couple of parallel twins - xs650 & cl450 with a cb360 thrown in for a change.

It has to be said that the k3 is turning out to be very civilized.  No great cloud of blue 2-stroke smoke.  It dosent send the cattle running for cover in the fields.  Dosent clatter and bletch great clouds of smoke in the small country villages.  I had forgotten what a different riding experience a 4 cylinder 4-stroke can be.

Having said all this I still keep trying for a 6th gear and concerned that its revving to high.  No doubt I will get used to its style.  Maybe its time to take a triple out for a day to get the perspective back.

Nairb   

[Johnny4428]

Hi Nairn, mine is also done 730 ish miles since rebuild, I am enjoying my K3 now as much if not more than I have ever done and I’ve owned the bike for 35 years. As Bryanj said on this forum these bikes prefer the higher Rev bands. That’s probably why the gearing is the way it is so these things are revving into their comfort zone. Although 60 mph mine is just over 4000rpm. Not sure of accuracy of gauges. Great bikes and underrated in IMO.