ET: Engine (Twin) Twin: rear engine mounting bolt F47/F83?

[brian gains]

For the hard of thought, can someone explain how engine expansion is accommodated in the rear engine mounting bolt assembly F47/ F83 with the cylinder bracket FT3 when hot. I can see that with the locknut slackened the motor can pivot around this point, but as the motor is fixed at the front head and lower mounting plates any expansion movement would surely just be linear and not rotational; what am I missing?

Also, does the initial smaller diameter shoulder on F47 and F83 fit inside the bored bolt hole of FT3 or does it just act as a spacer between the UFM rear mounting plates and FT3.

Thanks in advance.

 

[Peter Holmes]

Isn't any engine expansion taken care of by leaving the front cylinder mounting bolt loose but locked off, which allows for any ending expansion creep, all dealt with comprehensively in the Vincent book by Paul Richardson (otherwise known as The Bible. by me anyway) you must purchase and read this book.

 

[vibrac]

Some "Egli" frames I have encountered do not cater or this expected movement ie its a hole not a slot

 

[chankly bore]

It is the rear bolt that is slackened of by one flat from tight. The rear mount in the U.F.M. is slotted to allow for this, for compression plates and for variation of barrel height as well. Brian, sorry, is your machine the one in a B.S.A. frame? This explains the reference to "lower mounting plates" which would otherwise be incorrect.

 

[Peter Holmes]

Of course, the rear bolt, should have taken my own advice and re-read Richardson before I posted, isn't this memory loss thing awful!

 

[brian gains]

OK , thanks for that c. bore , I can see on closer look that the UFM plates have horizontally elongated holes and I guess the shouldered bush at either end of F47 has corresponding flats which I did not immediately appreciate from photos.

Yes, my query was with regard the VinBsa which I am going over. I had read horrific reports of the head cracking if there was no allowance for movement in this area. In my case the 'massaged' FT3 plate has independent (aluminium ) mounting plates bolted to the frame and I am considering how to introduce allowance for expansion. Does anyone have the larger and smaller diameter measurement for F83?. I am also thinking that the aluminium plates ought to be replaced with steel to make more durable/robust.

I may as well confess now, probably better suited to it's own thread, but Dick Sherwin saved me from humiliation by submitting a photo of the LHS of the machine therefore not revealing that it is a chopped motor with a Norton box. I had naively thought this was done as an economical and acceptable replacement for an original box that had suffered a catastrophic failure. However reading around the subject I now realise it was more commonly done just to shoehorn the motor into a frame with questionably better handling characteristics. I don't mean to start a bun fight but apart from production hybrids I must say even I find this a heretical practise.

 

[BigEd]

Isn't any engine expansion taken care of by leaving the front cylinder mounting bolt loose but locked off, which allows for any ending expansion creep, all dealt with comprehensively in the Vincent book by Paul Richardson (otherwise known as The Bible. by me anyway) you must purchase and read this book.

Rear cylinder head? #1.

 

[Chris Launders]

Chopping the original box off was usually done by people racing them wanting a quicker changing box with a range of ratio's, my Norvin crankcases had been chopped when I got them, they were part of a job lot someone got, a grasstrack outfit with with a full engine in and 4 spare sets of chopped cases (this was in the 80s). I don't think many people chopped them just to fit them in something else.

 

[davidd]

There are a substantial number of Eglis running with the engine bolted solidly into the frame. Despite many of these being very high power engines none of them have seemed to cause any problems related to temperature. I would not dismiss it as a potential problem. I know the Phils did a lot of work on expansion caused by temperature, it just has not been a common problem in practice. I have also seen Eglis with no bolt (and no hole) in the rear cylinder lug.

I am not certain that I would call cutting off the gearbox "heresy". Again, a lot of work went into designing the gearbox specifically to be cut off. Doing so would not have bothered Vincent or Irving considering they designed it to be cut off easily. For the most part it is a lot of work and usually makes little sense.

David

 

[macvette]

The UFM bolt on series D model rear heads is fully tightened. So no expansion slot.
Mac