Compression on 40-50's Td +Tn 5HP

Scaaty

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What can I expect in the way of compression on the old Johnny Td-20, Tn 25-28 twin 5 HP? Have three blocks, one in the 60's, 2 at 70-75 on a good yank after squirting a little WD in there. Probably a touch carboned up, and have been sitting (long time), but still spin free. This good enough to make a runner, or need a tear down? Thanks
 

JB

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Re: Compression on 40-50's Td +Tn 5HP

I would call all three good to make a runner, SCAATY
 

Scaaty

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Re: Compression on 40-50's Td +Tn 5HP

Thanks JB! And from what I recollect, these are "roller" motors aren't they? Needles crank and rod? If so good for another 50 years after a little de-carb.
 

Paul Moir

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Re: Compression on 40-50's Td +Tn 5HP

They are not. Stick with 24:1. They will last a very, very long time though. They're not know for rod troubles like the later 7.5hp.
 

Chinewalker

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Re: Compression on 40-50's Td +Tn 5HP

The compression numbers are decent. I would do a decarbon, though, as those motors like to gunk up with carbon in the exhaust ports and rings. The oils they used the first half of their lives were a lot "dirtier" than the ones of modern days...<br />- Scott
 

Scaaty

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Re: Compression on 40-50's Td +Tn 5HP

Thanks Scott and Paul (JB). I kinda think they would be fulla carbon, as you say, the oils used in the early years probably have crudded them up pretty well. Thanks for the heads up on the plain bearings. Stay wet.........
 
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