Honda CB400F2 Restoration Part Three
Series originally printed in Mechanics in 1994

Stripping The Engine

I took the frame and other cycle parts to A.W Smith of Darley Abbey Mills for blasting and enamelling. Mr Smith is a modest man, and does an excellent job. His speciality is restoring bicycles, so he knows what he is doing. His shop is an Aladdin's Cave, with jobs ranging from lawnmowers and bicycles to Jaguar alloy wheels and motorbike parts of all ages. He was not enthusiastic about enamelling the Honda's little brackets but was happy to blast them for me. He enamelled the frame, swing arm, stands and one or two of the larger brackets. All the small bits have been nicely cleaned-up, so it will be quite straightforward for me to paint them when the weather warms up.

While the dark nights were still with us, I prepared my first shopping list and sent it off to David Silver Spares. The CB400's steering head bearings looked decidedly tired so I ordered a set of taper-roller bearings. Other essentials were an oil seal kit, chains & sprockets plus gasket sets for the four carburettors.

I was due a couple of days holiday this week, so the engine was the target for my next attack. It was already sitting comfortably on a sheet of melamine-faced chipboard on my bench, so it was time to pluck up courage & get the spanners out.

The rocker box was the first to come off and lifted without incident. I was eager to see inside after 34,000 miles, and was pleasantly surprised with my findings. The cam follower pads looked remarkably good. With the cam sprocket detached from its shaft I was able to extricate the camshaft from the head. The bottom half of the cam bearings had not escaped so lightly and the cam lobes looked worn but, thankfully, not pitted.

Next came the head. Most of the nuts came away without incident. Unfortunately, two of them live outside the rocker cover, buried alongside the two inner spark plugs. Both had sustained considerable corrosion damage and were reluctant to come undone. The corrosion meant that neither had much in the way of corners for my socket to get a grip on. Out of desperation, one was undone by tapping an undersized Whitworth socket over the mangled nut. The second and last ( isn't always so! ) was not having any of this, and lost all of its corners in the struggle. The only way out was to split the nut by drilling carefully down through it. With this done, the nut was removed using a specially made long chisel to part it from its stud.

With the head off, Those four dinky little piston crowns were exposed for the first time. They really did look lost amongst all that cylinder finning. Luckily, there were again no nasty surprises. The valves all looked in good order. I was again pleasantly surprised, as early Honda twins and singles that I have worked on always had exhaust valves with bits missing.

I eased off the cylinder block to see if the good luck would hold out. Four bright little piston skirts peeped out, all with intact rings. I did not anticipate problems with the rest of the engine as it had always run quietly and smoothly. Dismantling the parts which had been bathed in oil was considerably easier than those open to the elements. I was annoyed that I couldn't get the alternator rotor off without a puller, but reasoned that it didn't have to be removed anyway.

The clutch and gearbox looked like they could handle an engine of considerably more power, and came apart without any special tools or pullers. Strictly, the clutch nut needs a special spanner, but because it doesn't actually hold the clutch onto a taper like a British one does, it is no problem to tap it undone with a suitable soft drift, once the tab washer has been released.

Compared with British and Italian machines, it was lovely to be able to just lift the crank and gearbox internals from the horizontally split cases without any huffing and puffing. It certainly helps with assembly as the parts can be simply dropped back in again in the correct order.

Having split everything into lumps, it was time to finish off the dismantling process and label everything up. Valves, pistons and rockers were all marked or put onto cards showing their correct position for reassembly. The valves were in excellent condition as were the seats in the head. A clean up and light grind should sort them out. The exhaust flange studs came out with the help of a pair of nuts locked on to the thread and a large application of heat from my rip-snorting blowtorch.

All the aluminium cases ( there are a lot! ) will be taken to Long Eaton Enamellers who make a beautiful job of bead blasting. Bill Woods seems to use much finer beads than others and gets a beautiful satin finish on aluminium. To make his life a little easier, I have degreased all the castings with Gunk.

I am impressed with the way the engine has survived, with two exceptions. I always wondered how Honda manufactured these SOHC cylinder heads as there seems to be no way that the bearings could be line bored. The simple answer is that they machine each half separately and hope for the best! I'm sure that my camshaft has never been anywhere near the upper half of its bearings. Secondly, Hondas of this era suffered badly from corrosion, but I didn't expect the problem to extend to the engine. Unless the fasteners are bathed in engine oil they need very careful treatment. I'm just glad that I replaced most of the Phillips screws with Allen headed socket screws fifteen ( was it that long!) years ago.

Next month, I should have a set of clean engine cases, newly plated fasteners courtesy of Derby Plating Services, and a painted frame. Time for some reassembly, I think.

Graham Curtis 25th May 1998

Thanks to the following suppliers who helped with the project

Tippetts Motors (Surbiton) Ltd
312-320 Ewel Road,
Tolworth,
Surbiton
Surrey KT8 7AW

Mick Bull Motorcycles
Unit 2,
36 Canal Street
Derby DE1 2RJ
Tel 01332 367470

David Silver Spares
Unit 14,
Masterlord Ind Estate
Station Road
Leiston
Suffolk
IP16 4JD
Tel 01728 833020

Derby Plating Services Ltd
148 Abbey Street
Derby
DE22 3SS
Tel 01332 382408