Engine & gearbox rebuild summary

This is a summary of the parts and specs for my 1969 TR6 engine and gearbox rebuild project, as a baseline and documentation for what was done.

Engine summary

Build completed and first startup: June 17, 2021

Car mileage: 78,xxx

Initial compression after cam break-in: 175, 180, 175, 175, 175, 175

Initial cam break-in and first 50 miles of driving were with Driven BR40 break-in oil. After that changed to VR1 20w-50.

Block: #CC56337E, a replacement from a '72(?) TR6. Bored to 0.40" oversize to clean up surface rust. Front aluminum oil gallery plug hole was retapped to 1/4" NPT and plug replaced with a standard steel hex plug. Large aluminum plug above the oil filter was replaced with a stainless steel 3/4" plug, installed with Loctite 620 retaining compound. Core plugs are nickel-plated steel, installed with Permatex #1. Most other gaskets are dressed with Hondabond.

Crank: short-back from '72 short block, ground to 0.20" under to clean up surface rust

Cylinder head: fully rebuilt, minor chamber smoothing and port matching, surface skimmed for cleanup. Height measures 3.43", which calculates to 9.47:1 compression ratio with 0.40 pistons.

Flywheel is non-original replacement to match short-back crank, new ring gear installed

Distributor was rebuilt by Jeff at Advanced Distributors and recurved to match new cam. His recommended timing is 14-18° BTDC at idle with retard module disabled. Retard vacuum module was rebuilt and is currently in use with a new vacuum valve.

New engine parts:

  • Bearings: King, bimetal, 0.20" undersize
  • Pistons: AE/Nural, 0.40" oversize, with stock rings. Pistons and rods were matched to balance within 2 grams, no machining for balance. Connecting rod bolts are ARP.
  • Camshaft: BP270 cam from BPNW, timed to 112° ATDC per spec
  • Nitrided HD lifters
  • Shorter 8.125" forged push rods
  • Dual valve springs from later TR6 spec, replaced original single-spring setup. New 1-piece exhaust valve retainers.
  • New intake and exhaust valves
  • Thrust washers: front is standard size, rear is 0.002" oversize solid bronze from Good Parts. Crank end float at initial build was 0.005".
  • Timing set: Renold chain, new sprockets from TRF
  • Front and rear seals
  • Front oil sleeve
  • Steel front sealing block
  • Oil pump - later alloy version
  • ARP head studs

Other related new/updated parts

  • Electric fan, and original fan removed. Fan is set up as a pusher on the front of the radiator, on home-built mounts. Fan is from American Volt, 16", rated at 12 amps and 2852 CFM. It has a manual override switch installed under the steering wheel and a thermostat control installed in the radiator downpipe. Fan extension replacer is from Good Parts.
  • Gear reduction starter to match new flywheel
  • Stock-style Bell stainless steel exhaust system from british-stainless-exhaust.com
  • Driveshaft was rebuilt and balanced by Proven Force
  • Adjustable jet conversion installed in carburetors
  • 2-piece plastic gearbox cover

Gearbox summary

All parts from The Roadster Factory. Syncro rings were measured well within spec, so were re-used.

New parts:

  • main bearings (RHP)
  • tailshaft bearing
  • countershaft bearings
  • input shaft bearing
  • layshaft (uprated hardened version)
  • thrust washers
  • 1-2 gear detent spring - weak tension for that selector
  • anti-rattle spring - broken in shifter

Clutch is a standard Borg & Beck kit, with throwout bearing. Fork got new pin and additional 5/16" shoulder bolt. New cross shaft and bushings, new pilot bushing, and all new hydraulics including stainless steel braided flex line.