Mastiff Engine part 4 - off centre tappets to cams

Note for Mick Knights re his Mastiff Engine - part 4 article

It could be that the intention of the designer for having the tappets / cam followers offset to the cam centre was to induce tappet / cam follower rotation. This was done on some production flathead engines many years ago to equalize the wear and to spread the oil around on the tappet shaft.

Just one explanation - there may be others. Cheers JD

Hi. Jeff.

Sounds like a plausible explanation. When I spoke to Kirk at Hemingway kits he told me it was an intentional part of the original design, but I was a bit too far down the line to carry out remedial work. Perhaps a note on the drawings to alert builders not using, or without the build notes to the different in hole centres on different components, but there again we are only talking a sixty forth of an inch on the original scale, which shouldn't have too much detrimental effect in the greater scheme of things.

Regards.

Mick

For Mick Knights

Help !

I am French and I am very interested in the construction of the Mastiff following your plans in MEW. Unfortunately I can not find your plans. Hobbystore does not have it. How to buy your plans?
I bought the plans of Masson in Hemingway, but I would like to have yours.

Excuse my bad English ...

Regards

François

Not only side valve engine, I've seen both OHV, OHC and DOHC has tappets slightly off center of the camshaft. The purpose is to get tappets to rotate and get even wear without gnaw directly on the surface. It contributes to the longevity of tappets.

Hi Francois. Your English is better than my French! The plans are from Hemingway kits, I've just multiplied each dimension by 1.5 to give the increased scale.

Hi Mick

Thanks for your reply

I have Hemingway plans

what I do not see, is how to assemble the 2 halves of the krancase: it has not much material to drill holes for screws to secure the halves ! And there are oil ways ...

Regards

François

If you are using the castings (original scale) then the crankcase is in one piece and I assume with all the internal features. If your making it from stock then there's no way you can machine the internal detail of the camshaft gallery without leaving the cutter radius in all the corners, you will also need long series cutters. I'm afraid you'll have to wait until the series reaches the stage when I tackle the assembly and the oil supply as its easier to show this with photographs. I do take the oil supply around the engine using external pipe work and the oil enters the engine from two ports on the sides at either end of crank case. The crankcase is held together by long series cap head screws, but you can't put these in until the oil ways and other features have been established. I used extra screws along the camshaft cover and the flange at the flywheel end for added strength. The two halves are finally secured using JB Weld, with all mating faces having a keying channel machined in them. Hope this helps.

Mick

Hi Mick

thank you, I understand better. I will actually waiting for the end of the articles.

I do not use the casting but I use a scale of 1.26 to easily convert in metric (inches multiplied by 32)

Thank you very much

François