Thanks for your reply,
@ richardhula,
Personally I think that approx 75% of de JP engines have the crankcase decompressor.
I noticed most of the 2 cylinders JP in UK narrow boats have a raised handstart and the decompressor is on the rocker cover.
Funny to see how they start the engine with a piece of rope on decompressor.
http://www.youtube.com/watch?v=xLWnzjEQ2jA
I managed to get my hands on a JP2 . the plate reads:
CS 75977
Spec: 18/2/35
RPM 1200
Please correct me if I am wrong, 18 HP at 1200 revs? And is it one of the latest JP2 build between 1930 and 1951?
Next month I hope to be her having home.
The JP2 looks nice and turns free, no frost damage and is dry stalled in a boat.
The only thing is that the starting handle hasn’t been touched for last 15-20 years.
Hi Bronssie,
Your JP2 is an industrial version built in 1950. The Spec: 18/2/35 suggests 18hp from two cylinders, but this is the historical model identification of nominal horsepower/cylinders used on other CS models, since the JP prefix was not used until later in the long production run. It refers to the power produced @ 1000 rpm, but would clearly be more at the plated 1200 rpm. The last number refers to build spec.
Most marine versions had 1200 rpm governor weights, with most but not all of the industrial versions governed to 1000 rpm I believe.
The marine manual I have dating from the 1960's quoted the JP2M as 23hp @ 1200 rpm. I imagine yours would be the same. Otherwise 9hp/cylinder was the norm with the single cylinder version always being known as the 9/1 not JP1 for some unknown reason.
The reason crankcase mounted decompressor versions are common, especially on the JP3/4's, was probably because so many were supplied during WWII to power searchlight and radar generating sets. As they were invariably hand start this location allowed the decompressors to be easily linked to a common bar operated by a foot pedal. Note that some marine versions were supplied with this type as well though.
Whilst many narrrowboats use the genuine marine version (JP2M or JP3M), the lack of availability of these has lead to many industrial engines being converted for such use. The best of these conversions involve placing the flywheel on the the other end of the engine as on the marine version, to allow a modern gearbox (usually PRM) to be fitted close coupled to the engine block, after its drilled and tapped to take a custom adaptor. The fitting of a starter ring shrunk onto the flywheel to allow electric start is a popular conversion with both variants since most didn't have this factory option.
For the record the marine version has a "dry sump" with external oil tank feeding pressure pump and return via scavenge pump, overhead hand start with chain drive to crank sprocket, and flywheel on the front (injection pump) end to allow the original Blackstone gearbox to be fitted close coupled at the other end. The exhaust manifold is water cooled with a matching water cooled silencer. A raw water circulating pump (gear or piston) was fitted with manually adjustable bypass to control engine temperature. Both types offered offered a bilge pump option twinned with the engine circulating pump. A closed circuit cooling system with its own pump was also an option. One of its crankcase doors would have reference to "R.A Lister (Marine Sales) Ltd." or "Lister Blackstone Marine Limited" on later models.
Although my own engine is a genuine marine version JP2M fully rebuilt by
Marine Power Services, they also convert two and three cylinder industrial versions to near marine spec with water cooled manifold/silencer, thermostatic engine temp control, electric start and swapping the flywheel end to end to allow modern PRM gearbox to be fitted, as shown and mentioned above.
Note the crankcase has already been drilled and tapped to take gearbox adaptor, also the external brass pipe to block from silencer. This is part of the marine cooling circuit with the pump feeding water through exhaust manifold to silencer before it cools the block/heads. Early marine versions used an internal passage in the block below silencer, dispensing with the need for the external pipe.
More info can be had by downloading this JP/JK 2/3M manual and parts list.
Good luck with your engine.