Author Topic: Valve springs for 500 OHV  (Read 313 times)

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Offline Cliffy73

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Valve springs for 500 OHV
« on: 08 Apr 2022 at 16:08 »
Hi can anyone advise me what are the best valve springs to use on a DT 500 engine. The springs I've got are for the long stem valve used o  the enclosed push rod and rocker cylinder heads with the swperate pedestals. Cheers Chris.

Offline Doug

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Re: Valve springs for 500 OHV
« Reply #1 on: 08 Apr 2022 at 23:16 »
The London Douglas Motor Cycle Club prewar spares carried the DT/SW5 valve springs. Have you checked with them to see if they still do?

I have a pair of the enclosed valve 1934-35 Douglas ohv models, so the later springs would be of interest to me. 

-Doug

Offline Doug

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Re: Valve springs for 500 OHV
« Reply #2 on: 08 Apr 2022 at 23:57 »
Just did a little checking and the outer spring for the DT as supplied by the Club is 1-3/8 inch o.d., 1-1/2 inch free length, and 0.147 inch diameter wire, with just a bit more than three full working coils.

A set in a 1935 ohv engine I have are identical. Though could have been replaced decades ago by a set intended for a DT, other than they are right-hand wind rather than left-hand like the DT.

A set measured from a 1931-32 F/G ohv model are again like the DT, except the wire is 0.126 inch diameter rather than 0.147, so giving a lower rate.

The road models used duplex springs where as the DT used triplex for the exhaust and duplex for the inlet. Presumably to compensate for the tendency of the exhaust valve spring to weaken over time due to heat. I have not come across any info as to what the SW5 used. The innermost spring of the DT triplex set was the same part number as the 350EW valve spring. The Club just sells (or did) the DT sets as the duplex, though they also carry the 350EW springs too.

If what you have are a set for a F/G31, then the rate maybe a bit low if you are intending on racing, but would be fine for road use. And clearly DT sets would also work in a road going machine, albeit a higher loading on the tappets and cam lobes. As you can see above, the lengths are the same and the longer valves used for the enclosed valve models just compensates for the greater distance introduced by the enclosed head and detachable perches. I did not compare the installed height, which might vary between the two designs and change the seat pressure. But if you can get the DT springs from the club, or the springs that you have match the DT dimensions, then as you are installing them on a DT type head the installed height on the enclose valve head is a moot point.

I did a study of the spring rates, and the new club DT valve springs (duplex) are 143.9lbs*inch. A used (and very rusty) set of DT valve springs had deteriorated to 122bs*inch, of which the innermost spring was contributing 16.2bs*inch to that total. A used set of F/G31 springs (duplex) was measured at 88.8bs*inch.

The following image shows the setup with force dynometer. Once resistance was detected the spring was compressed in 0.05 inch increments and a reading taken to plot the spring rate.   




-Doug

« Last Edit: 09 Apr 2022 at 00:09 by Doug »

Offline Cliffy73

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Re: Valve springs for 500 OHV
« Reply #3 on: 09 Apr 2022 at 10:07 »
Thanks for that Doug I will get in touch with the club spares. Do you know if they do camshafts as the one I have is bent and beyond use. Cheers Chris

Offline Doug

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Re: Valve springs for 500 OHV
« Reply #4 on: 09 Apr 2022 at 13:21 »
They don't do the ohv prewar camshafts. I had mine re-profiled to spec by a custom cam outfit here in the USA. Generally you will find one of two cams used in the DTs, The one stamped 10.5063.20 ans IN.OP.20 . The latter is also used in the 1934-35 road machines and I have seen the former as being stated used in the F/G31 models. So with a single carburetor thay make decent road camshafts.

I do make new tappets and adjusters for the DT, and a few other odds and ends advertised here on the Forum.

-Doug

Tappets:
https://www.douglasmotorcycles.net/index.php?topic=5054.msg18137#msg18137
Rocker spindels:
https://www.douglasmotorcycles.net/index.php?topic=5052.msg18134#msg18134
Valves:
https://www.douglasmotorcycles.net/index.php?topic=2141.msg7762#msg7762


 

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