bike grim wrote:I’ve just stripped a standard 1958 150 series 1 framebreather engine. I’m aiming to kit it. I’ve heard various things over the years about not using the standard mag housing but using a later one due to the single seal and petroil lubrication, and also about getting the casing machined on the drive side to fit an oil thrower washer etc but lately have had info from members that there is no need to do that. If that is the case and I use a gp crank, do I just order normal bearings? Are the seals available ? Any guidance would be appreciated.
Thanks Gareth
My belief is that the use of ANY magneto housing & the use of seals & the various bearings that fit is nowadays determined by what the engine builder thinks of primary compression. A standard nitrile outer seal will be fine, though I know some Forum users would prefer to spend more on so-called better seals. I've yet to experience a seal failure as the result of modern fuels.....
If a lower primary compression is desired, say, as might be the case in a racing engine with a good expansion chamber, then omitting the inner seal & ensuring good bearing lubrication with sufficient oil/air ways will enable the later magneto housings to be utilised.
A standard NU type roller bearing will cope & I see no reason as to why the earlier type roller bearing would not also be fine. Some racing engine builders use a specific 'magneto bearing' (a ball bearing) but there are, as ever, varying opinions as to whether the crankshaft is allowed to flex, or not, but the roller bearing type is far stronger in terms of dynamic load capability & the durability, an important consideration with a road engine.
I hope that helps
Posted: Tue May 01, 2018 3:43 pm
Martin Cook @ Chiselspeed said he has run race engines with S1 casings including Mag housing.