650cc Twin Cylinder Head Oil Restrictors

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650cc Twin Cylinder Head Oil Restrictors

Postby LynP » Sun Jun 09, 2019 6:36 pm

Hi, my query is about the oil restrictor jets in the fitted to the cylinder heads of twins which I believe were omitted in 1959 but re-introduced in 1961.
I am in the process of of re-furbishing the heads of a 1961 engine and I am pretty sure these are the original ones fitted to my engine when it was made. However, the heads I have are not fitted with the jets and so my question is. should I fit restrictor jets or leave it as it is? Can anyone tell me why they were refitted in 1961 and do they have any effect other than letting less oil to the top end?

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Re: 650cc Twin Cylinder Head Oil Restrictors

Postby robcurrie » Tue Jun 11, 2019 3:59 am

Less oil to the heads would mean more oil to the crankshaft.

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Re: 650cc Twin Cylinder Head Oil Restrictors

Postby LynP » Tue Jun 11, 2019 8:28 am

Hi, thank you RobC, I have had the crank reground so clearances should be as they need to be but should I fit restrictors or leave the heads as found? I am thinking perhaps I should fit restrictors.

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Re: 650cc Twin Cylinder Head Oil Restrictors

Postby 1608 » Tue Jun 11, 2019 3:16 pm

I fitted the restritors to my G12 with no ill effects. The top end doesn't need a great deal of oil and as said, it will probably mean a little extra oil elsewhere. As the r'tors were abandoned and subsequently re-introduced it makes sense to fit them to prevent over-oiling.

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Re: 650cc Twin Cylinder Head Oil Restrictors

Postby JEAN-NOEL » Tue Jun 11, 2019 4:01 pm

I agree with John : I would fit them to avoid over oiling in the valves area. On my engine there are 2 restrictors in the oïl channel, in one crankcase half, and two in each head.

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Re: 650cc Twin Cylinder Head Oil Restrictors

Postby LynP » Tue Jun 11, 2019 5:57 pm

My thanks you both 1608 and JEAN-NOEL. Looks like the restrictors are the way to go. My reservations about fitting them were based on something I read about the factory trying to solve the lack of oil getting to the drive side cylinder that resulted in the piston on that side seizing. Various solutions were tried like holes in the cylinder spigot on that side and the article went on to say this was not solved until 1962 when an opening was cast into the inlet cam tunnel for oil to fall onto the bob weight and be flung up into the that cylinder;(I wish I could remember where I read this). I do have a spare pair of 1962 crank cases with a opening/path cast into the end of the inlet tunnel, was this the factories final solution to the problem?
From reading the above I wondered that because the oil drains down from the rocker gear into the cam tunnels, would less oil going to the rockers because of the restrictors, mean less oil would drain down into the inlet cam tunnel resulting in less getting to the drive side bob weigh with a result that side cylinder could once again be affected as before.

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Re: 650cc Twin Cylinder Head Oil Restrictors

Postby JEAN-NOEL » Wed Jun 12, 2019 7:02 am

Hello Lyndon, I think that you have read "Service and overhaul manual", for twins 1955-1965, pages 6 to 13, of F NEILL. A lot of explanations on lubrication, oiling faults et c.
I had a look on twin spares parts lists for 1957, 1963, and was unable to see listed the oïl restrictors, nor in crankcase section, nor in head section ! Obviouly they are existing : they are in stock at AMOC PARTS, n° 018890. I can confirm : 2 in the oïl gallery, 2 in each head.

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Re: 650cc Twin Cylinder Head Oil Restrictors

Postby LynP » Wed Jun 12, 2019 3:51 pm

Hi again JEAN-NOEL, thank you for taking the trouble to check the spares lists and you were right about where I had seen the information on oiling changes, for some reason while I had looked for the information in other sources I did not look there. As and update on this post, I have checked the crankcases and there are 2 restrictors in the gallery. I will fit 2 in each head once the heads have been vapour blasted. Thank you to everyone who has taken their time to help me decide how to proceed. Good riding, LynP

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