Re: Snapey's 1935 Racing Biposto

Posted by Matt snape On 2011/3/29 7:27:39

So finally, after many, many months, I have organised the shed to accommodate the new Packard project. I have a clear floor and new benches so next on the list will be a trip to Wades Workshop to pick up the rolling chassis that I arranged to 'acquire' from him over a year ago now.

In the meantime I have not been idle and after stripping down the 282 engine that Wade virtually donated to the cause (I think it was in the way and he wanted it out), we have identified a number of areas that will need some further work.

Once the engine was mounted on a stand it was pulled down (not that many pieces in one of these) and cleaned up a little. My first concern was to check to see how sound the crank shaft was. If you have never picked up the crank from one of these, take my advice and have someone younger and fitter do it for you - I know it is a big engine but OMG this thing is heavy! Anyway, after much grunting it was hung from the roof on a piece of sturdy wire through a flange bolt hole and given what my father has always referred to as the 'ding' test. Take a 5/8 open ended ring spanner and give the suspended crank a nice solid tap towards the bottom end and you should get a nice, long, resonate 'dinggggggggggg'. If you hear a 'donk' it means you have a problem (most likely a crack) and a brand new door stop or garden ornament hanging from the ceiling. I got a really long, resonate 'dinggggggggggg...ggggg' that seemed to go on forever - so HWT... (Happy With That).

Examination of the main & big end surfaces raised some questions as most are quite poor, but one looks brand new and is possibly a reclaimed surface. Sizes seem pretty uniform though, so machining should be able to take care of this end of things. The main housings and caps all look sound, so should be no problems there. The conrods also look good and are much 'nicer' pieces than I expected for a large, slow revving, long stroke engine of this era. I would probably get them crack tested and then surface relieved first, but if the length is workable then I will most likely reuse them.

Pistons, on the other hand, are a different matter. Wade was kind enough to source some slightly used pistons from his personal stock and typical of Packard they are lovely things, but the alloy and steel 'strut' construction of these is not my preferred choice for a forced induction motor. Also looking at the bores I think they will have to be taken out at least 40-60thou to clean up properly so that means that Wades pistons won't be able to be used at this time either.

Given that this will be a 'performance' engine using period technology, then boring the block out for larger capacity would be one of our first considerations, so the next step is to find some pistons to suit. With a standard bore of 3.25" (out to 3.31" at 60 over) and with a compression height of (from memory?) roughly 2.125" this is not going to be a very easy task - although I am willing to consider a bore size out to near 3.50". Of course this might be pushing my luck a little and I can't really afford to machine the engine just to then sleeve it back down to standard. Decking the block to enable using smaller compression height pistons is a limited option since that would require re-machining all the valve head reliefs (read, more cost), although I am not likely to end up using the standard valves so the reduction in valve length itself would not be an issue. Either way, to use this block and get the larger capacity, I would like to go with the largest bore size possible. Either way it seems likely that we will be looking at either custom pistons on the standard con rods or larger pistons with a smaller compression height from some other application on longer custom con rods. Either way will be acceptable, but budget is always a concern so we will have to see what we can find in the books.

The cam shaft (aka the 'bump stick') hasn't really been considered yet, but that will likely also need testing and a carefully considered regrind. I will likely leave the research here to my brother as he has this nice little computer package that enables him to model cam profiles, timing, etc, etc, for the best performance and he'll get upset if I don't ask for his help. He also builds and rebuilds classic race cars and their engines and gearboxes for a living, so he is a handy guy to know.

So that is about the state of things at this point. Next time I hope to share some results of our research into engine internals and hopefully the chassis will be finding its way to its new home.