SQ4 engine noise

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torbjorn.vik
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SQ4 engine noise

Postby torbjorn.vik » Tue Jun 12, 2018 9:42 pm

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?
1929 Ariel F,1930 LF, 1934 VA31,1951 SQ4, 1957 Huntmaster, 1942 BSA WM20, 1927 Husqvarna mod 180,1969 Honda CD125, 1971 CB450, 1971 CB750

Knud.Degnbol
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Re: SQ4 engine noise

Postby Knud.Degnbol » Tue Jun 12, 2018 10:01 pm

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

nevhunter
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Re: SQ4 engine noise

Postby nevhunter » Tue Jun 12, 2018 11:09 pm

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

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paul.jameson
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Re: SQ4 engine noise

Postby paul.jameson » Wed Jun 13, 2018 11:41 am

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.
Paul Jameson
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GuyH
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Re: SQ4 engine noise

Postby GuyH » Fri Jun 15, 2018 6:59 am

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.
1939 600 OHV 4F, 1939 OH 250, 1939 OG 250 project, MF32 project, 1920 Ariel V twin project, 1956 Huntmaster and various odds and sods

torbjorn.vik
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Re: SQ4 engine noise

Postby torbjorn.vik » Fri Jun 15, 2018 10:49 pm

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.
1929 Ariel F,1930 LF, 1934 VA31,1951 SQ4, 1957 Huntmaster, 1942 BSA WM20, 1927 Husqvarna mod 180,1969 Honda CD125, 1971 CB450, 1971 CB750

nevhunter
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Re: SQ4 engine noise

Postby nevhunter » Sat Jun 16, 2018 2:43 am

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.


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