Seagull Engine Construction Diary

Making a 10cc twin 4-stroke to the E T Westbury design

Assembly and Finish

This section deals with an assortment of fitting and finishing jobs, leading up to final assembly, that don't really belong to any particular part.


2010-10-23 - Main Bearing Housing

I made a bush to align the cut-away in the main bearing housing with the camshaft hole. I used it to get the right position while tightening the sump bolt which hold the bearing housing in place firmly enough to allow it to be removed for spotting the holes through. After drilling, I tapped the six holes using the pillar tool to guide the tap. (1½ hrs)

2010-11-07 - Timing-End Bearing Housing & Lapping

Using the scrap timing end camshaft bush for alignment, I spotted the hole positions through to the crankcase and sump, and drilled and tapped as before and cut down a pair of 6-BA socket cap screws to the required 932″ overall length for the two extra holes by the camshaft.

Before starting work on fitting the crankshaft bearings, the end faces of the crankcase and sump assembly need to be checked and if necessary lapped flat and square to ensure that both bearing housings sit in their final positions. For lapping these faces I used 400 or 800 grit wet-or-dry paper (can't remember which) taped to my granite surface plate, with paraffin (kerosene) as a lubricant. First, I lapped the top face parallel with the sump joint face to provide a datum. It will still need a final rub before fitting the cylinders, even though the overall height is now 3 thou undersize. Moving to the timing-end face, the sump face was very slightly high, even with the main bearing housing bolted up tight. I lapped this face flat and square. Although the flywheel end blued up square and not far off flat, I still lapped that too, although largely to look right. The resulting smooth, slightly matt surface looks so much better. Next job: lapping the bearings. (2 hrs)

Timing Case

2011-12-21 - Trial assembly

With Timing-End Bearing Housing and Timing case full machined, and the Idler Stud made, it was was time for a trial assembly. Trying the gears, the crankshaft pinion and idler ran were good but the idler and camshaft gear have come out quite a bit too tight. This will need further work. The fit of the timing case depends on the dowels, the idler stud and the crankshaft sleeve, and it is not surprising that this will not go together comfortably without fitting work. (1 hour)

2011-12-30 - Easing

Having pushed the timing case home I found I needed to warm it up almost too hot to hold before it would come off in the hand. I also need to put tapped forcing-screw holes in the bearing housing to make it easier to dismantle without having to slacken the sump securing bolts as well. I refitted the idler stud in its chucking bush and polished it until it went fully home with a shake-free easy push fit, but the stud and dowels are still in conflict. The fit is free until it the case is almost home, and carefully easing the hole a little with a hand reamer makes for an easier fit. (1¼ hours)

2011-12-31 - Assessment

The crankshaft sleeve turns sweetly in the timing case. The assembled crankshaft and sleeve turn with a half-turn a little stiff when running in the timing-end main bearing and timing case. Fully assembled, with a full set of bolts holding the timing case in place, there is some stiffness, but I think it will bed in OK. The idler pinion was also stiff on its stud when home to the shoulder. This was soon cured by polishing over the oil hole in the stud with 1200 grit wet-or-dry paper. The gear train will have to be investigated further, as it is too tight to expect it to run. (2 hours)


2015-03-04 - No 1 Cylinder assembly

After trimming 6-BA cap-heads to fit, I prepared No 1 Cylinder assembly for blasting by blanking off all the exposed machined bits. Straight out of my new blasting cabinet, the result looked nasty because of staining from porosity, mainly of the cylinder casting. Given a paraffin (kerosene) wash, a hot soapy water wash, and a wipe with light oil, it looks a lot better and blends in with the crankcase parts similarly finished some time ago. (2¼ hours)

2015-03-05 - No 2 Cylinder assembly

Today I went through the same procedure with the other cylinder. (1¼ hour)


2015-03-06 - Lapping the manifolds

As a diversion from making tiny studs, I spent a little time lapping the main joint faces of the mainfolds, using 600 grit silicon carbide paste on a glass plate. After carefully cleaning up, I tried the inlet manifold on the surface plate. It blues up perfectly with with a very thin smear. (1 hour)


2015-03-21 - Studs and washers all made

With all the castings (except the carb body) finished, fettled, and sand blasted, and all the studs and washers made, I thought it was time to go for a trial assembly to see how it all looks. This was just the castings, I did not put any of the moving parts inside. The timing case is not pushed fully home. I think the apparent unevenness of the head studs, which are individually measured, is largely down to variability in the thickness of the commercial nuts. For the inlet manifold I have used some more recently bought nuts that are 6 BA with a 7 BA hexagon: washers for the standard size would have overlapped the casting.