The Bonneville Project

Engine rebuild complete

After undergoing major surgery, the engine and gearbox unit unit has finally been rebuilt.

This involved a complete strip down and nut-and-bolt rebuild, replacing any worn parts along the way.

Bearing in mind the bike started before the restoration, I was in two minds whether a complete rebuild was necessary.

It was expensive - costing £800 in labour alone - but peace of mind counts for a lot and it was a job I couldn't have done myself.

There are about 380 different components in the engine and gearbox unit, according to a quick scan of the replacement parts catalogue, excluding multiple quantities of nuts, bolts and washers etc.

My rebuild, which was carried out by John at Barnfields Classics, involved replacing about 40 components.

Parts replaced included pistons, main bearings, the wrecked drive side cover, exhaust tappet, clutch chainwheel, primary chain, con rod bolts, and inlet and exhaust valve guides.

The rebuild also revealed that the sludge trap was completely blocked, which could have been nasty had I ridden the bike with the engine left as it was.

Anyway, all the replacement parts and prices are shown in the table below.

You'd probably better sit down while you're scrolling through the table.

Like many projects, an outlay like this virtually guarantees that the bike will end up costing more than it will be worth.

So it's a good job I won't be selling it.

Part No.	Description	Price	Quant.	Total
70-11078	Primary chain oiler	1.75	1	1.75
70-4565	Nut for clutch	2.29	1	2.29
70-3975	Tab washer	0.78	1	0.78
70-6576	Con rod bolt	6.58	4	26.32
70-3827	Inlet valve guide	13.47	pair	13.47
70-3828	Exh'st valve guide	13.48	pair	13.47
82-0879	Rocker box nuts	1.83	set 6	1.83
70-3302	Washers for above	1.13	set 6	1.13
70-4568	Timing side seal	4.47	pair	4.47
70-7565	Oil seal	2.06	1	2.06
70-4144	Rubber grommet alt wire	1.08	1	1.08
70-8801	Exhaust tappet	35.02	1	35.02
70-7563	"O" ring	0.33	1	0.33
21-1866	Stator stud long	6.50	2	13.00
21-0044	Domed nut drive side	4.94	pair	4.94
21-0586	Clutch securing nut	2.91	1	2.91
70-1511	Small end bush	7.52	2	15.04
70-3586	Big end bearing std	21.29	1	21.29
57-2240	Tab washer mainshaft	0.94	1	0.94
57-1919	Main sprocket	17.01	1	17.01
T-946	Oil seal high gear	4.52	1	4.52
70-1591	Main bearing	38.69	1	38.69
70-2897	Main bearing left	24.00	1	24.00
70-3876	Oil seal	2.47	1	2.47
70-3905	Plug sludge	3.24	1	3.24
70-3903	Sludge trap	6.82	1	6.82
21-2016	Conrod selflock nut	0.79	4	3.10
57-2526	Clutch pressure nut	6.49	set 3	6.49
57-3931	Thrust washer	3.88	1	3.88
57-0394	Clutch rollers	6.11	set 20	6.11
70-6061	Chain tensioner blade	12.93	1	12.93
60-0477	Primary chain	23	1	23.00
70-9488	Piston kit	82.91	1	82.91
70-8287	"O" ring	2.47	2	4.94
70-4568	Oil seal point side	5.17	pair	5.17
71-1707	Pair of fibre seals	3.88	1	3.88
	Gasket set	25.00	1	25.00
	Camshaft bush set	25.00	1	25.00
	Plating	30.00	n/a	30.00
	Alternator grommet	1.47	1	1.47
	Drive side cover	50.00	1	50.00
	Screw set (cover)	11.75	set	11.75
	Clutch chainwheel	29.37	1	29.37
			Subtotal	583.87
	All prices in GBP		Labour	800.00
			VAT	included
			TOTAL	1383.87

 

Replacement cylinder head

Firing up the bike before the restoration revealed a lack of compression on the right-hand-side of the engine.

Removing the spark plug revealed the problem - the plug hole was quite extensively damaged and needed repair or replacement.

A basic repair would have cost £50. But the damage was close the the valve seat, and the inside of the cylinder head was in any case rather rough.

I decided it would be easier - and cheaper in the long-run - to replace the cylinder head entirely.

By chance, I found one on Ebay - stamped on the inside with the number 68, meaning it was manufactured in 1968 - exactly the right year for the bike.

It cost me £141 (including £10 postage and packing).

Primary cover disaster

When this bike slithered down the road in 1973, it did so on its side.

The accident caused extensive damage to the bike's left-hand-side and caused the insurers to write off the bike.

It also bent two bolts that attach the primary cover to the crankcase, ripping them through the metal.

Bolts and cover must now be replaced - but fortunately there is no other damage inside the chaincase itself.

Even so, it's another purchase that has contributed to a growing feeling that the project is going to cost much more than I thought.

This uneasy state of being plagues most restorers - as well as their partners.

So I've decided to go through the whole bike and catalogue everything that I need to buy.

That way I will get an overall cost for the project and settle my mind. It will also mean I can order items in bulk, cutting down on postage costs.

Of course, I should have done this at the beginning, but had I done so I probably would never have embarked on the rebuild...