Sat 29th Aug 10.
I've mostly been working away this week, it's been quite a few miles of travelling to Gloucestershire and Berkshire on the BMW GS1150 (Yes I know... my daughter never ceases to remind me I must be getting old, but I honestly can't think of a better bike to do this mileage all year round).
I started the week involved with a Bentley engine from the late thirties. This has been rebuilt by a specialist company that always work to very high standards. Although carefully run in on the road, unfortunately this engine has given many problems with piston ring and cylinder "bedding", through no fault of the builder.
This is something that I have come across before and something that we are all at some risk of encountering during the restoration work of the older engines.
Some particular makes of aftermarket pistons and rings can bed very poorly especially with some cylinder materials. Experience and chatting to other builders can enlighten you as to whether a particular make might not be compatible but even then it can still cause many hours of worry.
Whilst working for one particular engineering company we ran into real problems of a mismatch between a particular aftermarket piston and a particular pre war car model.
Unfortunately we were caught in the middle, the piston company required the engine to remain stripped for analysis and the customer needed it together to keep the owner as satisfied as possible.
The best option in this case was to have new rings independently manufactured and fitted, therefore the piston manufacturer never really had the analysis or proof of component failure.
The correct running in procedure can also be critical. I have found an excellent article in the book "Four Stroke Tuning" by Alexander G Bell .
Aside from the mechanical/ physical problems caused by materials or final tolerances, there can be other causes of poor bedding in:
The correct lubrication is important, however, you may see different scenarios.
A newly built Morris Minor engine for example, may be filled with a reasonable quality oil and driven very carefully by a very conscientious owner/builder, only to have problems in bedding in.
The same engine however, run on a dyno under a strict criteria might quite happily have bedded in, even perhaps on a very high quality oil.
Incidentally, there may have been a "last ditch" rescue for the careful owner, that is the use of a very thin and aggressive running in oil for a short period of hard driving (Castrol Oils offer a very good helpline for this type of service).
During my time with the engineering company,I would often judge the character of the owner of the newly built pride and joy and perhaps strongly suggest the use of a dedicated running in oil from the outset..
Back to the Bentley.... The engine, recently fitted with another set of pistons and with new liners was set up and run on the dyno through a strict sequence of procedures. Torque loadings indicated that the rings and pistons were bedding in nicely and the initial crankcase breathing fell to a minimum.
We carried out a fuel air ratio check and checked all temperatures and pressures.
Just for interest a power sweep was carried out showing a torque figure in the region of 220ft lbs and about 120HP @ 3800rpm ( I will not disclose the exact figures).
Also this week I've continued on the restoration / refurbishment of an Alfa Romeo 6c, again dating from the late '30s and again at the customer's premises.
The Alfa is such a beautiful car, not only it's stylish although flamboyant design. But also the engineering is to such a high standard, very expensive but very correct engineering, this is such a nice project in this way.
I am currently involved reassembling the individual components of the suspension, each item having had any necessary engineering recovery work.
Some further finishing work on the rolling chassis of a restored Aston Martin 15/98 from 1937.
Followed by the continued build/ pre build of the C.I.M.E. engine for an early to mid '20s GN.
I have been fitting the piston rings on to the pistons, but first I've checked each ring to each respective cylinder and dressed the ring gaps carefully to size. Very time consuming..