Saturday, August 27, 2011

JAP 4B Racing Engine For Sale

                                                                  J.A.P. 4B Engine

On offer is a J.A.P. 4B long stroke racing engine from a parts stash out of
the Midwest Cooper F3 racing fraternity.

The engine was pulled from a racer years ago to be rebuilt for a new race
season which, for various unknown reasons, never happened.
This is the same 4B engine that was run in flat track, dirt track and grass track motocycles.

In preparation for the rebuild the case was cleaned and the inside coated
with red glyptol and the outside was given a spray of gray for corrosion
control on the lectron/magnesium case. The engine has had the flywheel and
main bearings fitted along with the con rod.

All other parts have been dry fitted before final tolerance and proper
honing and fitting.  The engine has no seals with it and must be considered
a complete but unassembled engine.
The parts provided are as follows;

  Glass beaded steel head
  1 1/4 inlet track has a good nut and carb flange which has been blended
into the head intake port but not polished.
  Good threads on exhaust outlet and chromed exhaust nut with a nice
smoothing of the exhaust port but not polished
  New Titanium valve spring caps and keepers
  New stainless steel valves - 1 ¾ intake - 1/1/2 exhaust
  New valve springs
  New steel valve guides with the option of alum/bronze if desired
  Valve rocker and bushings with needle bearings are original equipment in
good condition
  Complete rocker box with a small crack in the bottom edge of one rear
spring cap
  Oil line from pump to rocker box and secondary feeders from rocker box to
valve guides but oil pipe unions will have to be sourced for the build
  Lodge Pink spark plug (SL51?) maybe just a place keeper
  New Carrillo H-Beam rod
  New 80mm Arias domed racing piston with rings
  Case cleaned and coated for corrosion protection on the outside and oil
shedding on the inside
  Wellworthy ALFIN barrel- good fins and good clean steel sleeve
  4 compression studs for head to case - good threads - stud appearance fair
but useable
  Pilgrim oil pump - used but on inspection appears good
  Oil box has in place four oil return valves
  Polished roller valve lifters
  Valve cam with unknown profile
  Flywheel has been polished and balanced - unknown balance percentage
  New alloy push rods with good ends
  Chromed push rod tubes
  Magnesium timing side cover, oil box cover, oil return box and magneto
  SEM magneto which sparks but has not been tested and needs cleaning and
new points cap
  Drive side splined carrier and retaining nut for drive cog
Unknown maker bronze mechanical tachometer drive to run off the magneto
shaft with cable drive end which should, with appropriate cable, drive a
Smiths Chronometric tachometer

Engine has been dry assembled only for the purpose of checking parts fit and
inventory of parts.  This engine has not been built as it is excess to my
requirements.  What would be required is cleaning and fitting of all parts
to specifications.

My Overland cycle needs only one engine and so this engine which as they say is excess to my needs has to find a new home.  I would very much prefer it go to a home that will run it.

Anybody with an interest in this engine please leave your contact information as a comment and I will get back to you.

                                                       The simplicity of the J.A.P. 4B

This is a photo of the for sale engine before dry assembly to check that everything was there.


  1. hello, i just want to know about the above picture. do u really want to sell that engine?

    please send some pictures if you really to sell it to


  2. Good engine and post. By the way if your looking quality engines just like this one. I totally recommend this site for you.