WHEEL SIZES

There seems to be a great deal of confusion over the different wheels fitted to lsettas, and nobody really knows the full facts. However, this is how I imagine it should be:

The front wheels of which there should be two, are narrow, by which is meant 300 x 10. They have stud holes that are made to take the normal wheel nuts from the outside.

The rear wheel is wider, at 350 x 10, and has the stud holes drilled out so that the wheel can be fitted in the way that is peculiar to the rear of the Isetta. The spare wheel should be another narrow one, but with the larger holes, so that it can be used at either end of the car. In addition the centre of the spare wheel should be offset in relation to the rim to allow clearance over the rear hub.

The front wheels and the spare should be fitted with 4.80 x 10 tyres. The rear wheel, and the fronts on many cars, is fitted with a 5.20 x 10 tyre. These dimensions apply only to three wheel British built cars with one-piece wheels.

HINTS & TIPS ON STRIPPING & REBUILDING A BMW ISETTA ENGINE

1. The advance/retard unit, commutator and fly wheel are really only effectively removed with suitable pullers. Such pullers are available from the Club's spares. A flywheel puller can easily be made up from scrap metal. The threads in the flywheel for locating the tool are 3/8ths" UNF. With tapers, the trick is to be patient. It will give eventually. Try not to use extreme force. Something may break and cause more trouble.

2. If dismantling the crankshaft assembly, ensure the oil slinger plate fitted to the front with a countersunk screw, is cleaned out. A hard crust of oil and dirt particles gather in the channel. This unit, and the gauze at the bottom of the crankcase, are your only means of oil filtration.

3. When removing the timing cover remove all nuts and bolts (don't forget the countersunk screw on the RH side). Warm the cover slightly with a blow-torch in the vicinity of the oil seal. The supporting bearing here is a slight interference fit in the cover. Release the cover by using a soft hammer on the back of the cover. NEVER wedge a screwdriver between the cover and the crankcase.

4. When removing the cylinder barrel there are very few places to knock to remove it. Again, a screwdriver shouldn't be used. The best way here is to remove the head and the securing nuts on the barrel. Now put a small square of wood into the bore, place the piston well down the bore and re-fit the cylinder head temporarily. Now rotate the engine by the front securing bolt (if fitted) and the force of the wood touching the valves lifts the head and the barrel off the studs together. This avoids any damage to the delicate cooling fins on the barrel.

5. When checking the big-end for play only take into account up and down movement. Sideways movement is always present.

6. If the crankshaft sprocket has to be removed - its a tight fit. A heavy-duty or better a hydraulic puller is required. Heat up the sprocket to help it along.

7. The oil delivery plate for the timing chain should not have the pipe obstructed. A worn timing chain will burr over the pipe, thus restricitng the flow. Repair or replace the plate if damaged. No oil flow will wear out a new chain rapidly.

8. When re-fitting flywheel, ensure it seats correctly on the woodruff key and secure nut to about 110 lb/ft, using a small amount of Loctite on the nut. The nut size is 36mm or 17/16th".

9. When re-fitting the clutch assembly use three bolts about double the length of the originals for fitting purposes only. The longer bolts will have to be threaded all the way up and a nut used on each to draw the clutch assembly to the flywheel. This compresses the diaphragm. The clutch friction plate must be centred by sight or with a home-made tool. Once the spring is compressed the normal bolts can be fitted in the three remaining holes, then the longer bolts removed and the remainder fitted.

10. The cylinder head, being the weakest part of the engine (as those who have had a valve drop will confirm) needs special attention. If possible, valves, guides, springs and collets should be replaced, although a little expensive. At the very least, the exhaust valve and guide should he replaced. All new parts are available at the club spares store.

11. About the most awkward part of rebuilding an lsetta engine is the timing chain refitment and valve timing. The only timing mark to help you find theTDC of the crankshaft is on the flywheel. There are no marks on the camshaft sprocket. The method given here assumes the engine is in its basic rebuilding stage, i.e. piston, barrel and head not fitted. Fit the camshaft and followers. Ensure the crankshaft is at TDC by aligning the OT mark with the centre of the cut-out of the crankcase. Now rotate the camshaft sprocket and note when the followers are just rocking i.e. the inlet just starting to open, exhaust just starting to close. In this position, look at the camshaft sprocket. There are two holes in it and through each hole should be seen about a 1/3 of each camshaft securing screw. In the left-hand hole it is at the top and at the bottom in the fight-hand hole. Be careful not to position the sprocket 180 degrees out because in this incorrect position the followers aren't rocking, of course. Now feed the timing chain around, keeping the timing correct. If the original chain link is availablejoin the chain together from the front. Now rotate the engine until the link is above the recess at the bottom of the crankcase. Now the new link can be fitted from behind - easier said than done! But with patience and long-nosed pliers plus a small Allen key to pull the new link into place from behind, the old link can he pushed out. A new spring clip is fitted with the closed end facing the direction of rotation (clockwise). Now rotate the camshaft two complete turns and re-check the alignment. Incorrect valve timing will make the engine either not run at all or it will be lacking power and back-firing.

12. Finally, when re-assembling, use gasket sealant on all but sump and cylinder head to ensure against oil leaks BUT use sparingly and avoid blocking oil supply holes with sealant.

After the engine has been run until hot, wait until it is cool and then check tightness of head bolts and barrel nuts. RE-check valve clearances. Oil should be changed at about 500 miles and the running-in period should be at least 500 miles but preferably 1000 miles if you can stand the lower speed for that length of time. The top speed while running in is 40 mph MAXIMUM.

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