SQ4 engine noise

[torbjorn.vik]

Hi, some may remember I had a problem with the oil vacating the engine through the crankcase breather. I followed the various tips I got on the forum, blew through all the oilways with compressed air, found that the washer in the oil pressure regulator had been put in the wrong way and put everything back together. It now keeps all its oil inside, both when running and afterwards. Starts easily, idles and responds nicely. However, when under load there is a persistent ticking noise which follows the increase in revs, like there is a very large valve clearance gap on one valve - which is not the case. The noise disappears when easing off on the throttle. Any ideas? Should I just use it as is or is this an indication of some imminent failure?

[Knud.Degnbol]

Could it be pinking caused by low octane petrol or too early ignition?

[nevhunter]

Have you got wear in the coupling gears? Check in numerous positions. That would be worse when hot. If that is the cause it won't hurt the engine but may annoy you. Nev

[paul.jameson]

Check whether one or both of your coupling gears are loose on the shafts. The easy way to do this is to remove the front crank end cover on the timing side, put the bike in gear, rear brake hard on and see if you can rotate the front crank at all in either direction using a suitable spanner / socket. If you find some movement, take off the timing cover and see if the movement co-incides with movement of the rear crank. If it doesn't you have a loose coupling gear or gears.

[GuyH]

This was an issue recognised by Ariel and page 8 of their 1939 - 46 Square Four owners handbook has a paragraph explaining that owners may hear a metallic knock when riding a square four at low revs when the engine is hot and:

"it is almost certainly due to the small initial clearance allowed between the teeth of the crankshaft coupling gears. The knock arises from the alternations of power impulses on each crankshaft. This noise is perfectly harmless and can be ignored. However if you wish to eliminate, retard the ignition somewhat and/or drop to a lower gear"

I found the noise pretty disconcerting when I first heard it and, like yours I found it wasn't just at low speed but also as I accelerated but the noise cleared once I was cruising at a reasonable speed.

[torbjorn.vik]

Thanks everyone! It’s not pinking; I know what that sounds like. I do not believe there is any significant wear in the coupling gears as as almost everything inside the engine is either new, nos or professionally reconditioned. Including each and every bearing. I think I’ll go with the explanation from GuyH and continue to ride it for a while. And then carry out the test described by Paul J after the driving season is over.

[nevhunter]

It's my understanding that these gears are ground to final size when new as one would expect to get the required accuracy and matched at assembly initially. The cases heat and expand more than the gears so absolutely quiet running is unlikely when the engine gets hot. They include a sound absorbing cover and absorbent material in each gear . It's there for a reason.. Nev.

[merrick marshall]

Hello, dont seem to get on the forum much. Though ,i am having trouble identifying an knocking, intermittant noise coming ,when at idle or low revs. Saw this thread and struck a chord. Ive had the primary side off numerous times and redid the end float on the rear crankshaft,via the timing side shimming. Thought i had found it, but no. Less but still there. I know it says in the manual about ringing of the coupling gears and as i haven't seen /heard another SQ 4 to compare it with. I dont know if they all do THAT. Ive reset the valve timing, and It now speeds along lovely. No noise then. The clutch could be a contributor , but again do they all do that? Will check the tappets again and a couple of other things. Have had the stethoscope on the bearings and nothing sounds terninal. My memory now seems to be fading and i wonder if it was forever like this..... Is there someone out there in the merseyside area who i can share my burden. Have taken the sidecar off to sort this problem? out. Kind regards.

[KenGriggs]

Have you checked the primary chain tension? Sometimes the gearbox can move backwards slightly, if it isn't tightened enough, under the load from the rear wheel. That can cause the primary chain to become very tight, and cause a noise under acceleration. The gearbox mounting bolts both top and bottom need to be very tightly fastened to prevent movement.

[merrick marshall]

Hi Ken , Done that. Have had the complete primary side off and reattached the clutch and started it up. Usually do it blindfolded now, with a steven seagal bandana around my head. I have tightened the mounting bolts up so no way should it be able to move.