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MG MGB GT V8 Factory Originals Technical - What constitutes a 'good' conversion?

A lot of you guys can seemingly walk up to a V8 conversion, look at where the steering column comes through the firewall into the engine bay, and say in six seconds whether a proper conversion job has been done. What are you looking for? What do you look for in general? I am hoping to purchase a V8 conversion (Rover or BOP) -- don't have the time, tools, or know-how to pull off the entire project myself -- and I am wondering how to assess it. My tastes run toward GTs, but since almost all of them are chrome bumpered cars, I realize converting them is around twice the effort and the likelihood of it being done wrong is higher, so I will probably get a roadster. If you are reading this, Roger Parker, Glen Towery, J Hesser or anyone else in the know, what moves do you want to see before pronouncing a conversion sound? What are pitfalls to watch out for?
Matt Wilson

I think the most important criteria in judging these cars is CREATIVITY. I really dislike the term "proper" - it's okay for restored "factory" cars - but I hate to see it applied to CONVERSIONS. These cars should reflect the creativity as well as the craftsmanship and engineering skills of their creators.

Too many converters use cheap hardware, and when they design brackets they tend to put bolts in "single shear", which is a cardinal sin. I've seen some pretty ugly wiring on conversions.

People talk a lot about cooling these engines - I don't understand why some people make cooling system fabrication look so difficult! Fans should be shrouded - both for safety and for cooling efficiency. Radiators should be mounted so the whole core area gets used, so they're easy to fill and to check coolant level on, and so air at the top of the radiator is easily purged. Radiator mounting brackets should be robust - but regretably most aren't.

Personally, I have a huge preference for chrome-bumper MGs. They're just better...

I like roadsters in general, but GT's are stronger than roadsters to begin with. Also, I can't prove it but my observation is GTs seem to age better. (My belief is their floorboards rust less, since they don't get caught in the rain with their top down.) Anyway, chassis strength and rigidity is important for a V8 powered MGB....

Curtis, for us laymen ... what does it mean to put a bolt in "single shear"? ... what would be an example?

Single shear is when a load is applied only to one side of, say a bolt. Imagine, for example, a tube shock bolt- if it simply goes through the shock eyelet and into the chassis, it can be considered to be in single shear. The bolt experiences the downward force of the shock on one side and an equal reaction force on the other (the part that is in the chassis). Over time, if you examine the shock bolt you will find that it might no longer be straight. The part that went through shock will have been pushed down and the part that was in the chassis pushed up, kind of like it was trying to be pulled apart - sheared.
Double shear (which is what you want on something that will experience tremendous shearing forces) is when that same shock bolt is displaced in three sections instead of only two. For example, this time imagine that the shock first goes through a solidly supported bracket, then thorugh the shock eyelet, and finally into the chassis. The shock eyelet is sandwitched between the bracket and chassis. The bolt will experience a downward force on the part that goes through the shock. There will be a reaction force produced by the bracket and by the chassis in the opposite direction to the shock force. If you were to later examine the bolt you might find that the bolt has deformed - having a dip in the section where it went through the shock eyelet, kind of like a section of the bolt was trying to be punched out.
In other words, double shear divides the reaction forces in two and greatly reduces the chance that the bolt will fail. It spreads out the force into a larger area. This is much easier to see that explain in words.

Sorry to be technically picky, this does not change what I said, but I did not mean to imply that a reaction force is a shear force- for anybody that cares.

Wow. Joaquin has provided such an eloquent and complete explanation, I've nothing to add.

Except maybe I was a little arbitrary to pick that one gripe (single-shear bolts) to focus on
when there are so many hardware related "sins". Fastener failures seem particularly likely to
be catastrophic, or at least especially inconvenient. (Plumbing failures would be right up
there too.) Carroll Smith's classic book "Prepare to Win" - would be a great start for anyone
who wants a quick education that's not specific to MGB-V8's.

Other gripes: applying bolts in shear applications where their threaded sections are in the
plane of the joint, so their effective diameter is reduced and stress is concentrated at a
thread. Or failing to design for bolt/stud "pre-load", so fasteners can't be properly torqued-up,
and therefore inevitably vibrate loose. (Special efforts, like self-locking nuts might then be
seen - but sometimes they're used instead of a "better" solutions such as possibly use of a
spacer sleeve through a soft or crushable material so the fastener can be torqued better.)
I haven't met THAT many MG-V8 owners, but I've heard of and seen a lot of failures right
around the alternator bracketry.

Irrespective of visual aspects the resulting car must retain the original balance between all the dynamic aspects and safety. It is very easy to plant a 6 litre motor that is capable of ripping the chassis apart but this simply creates an animal.

The other aspect is that the car should be still as capable of being driven slowly and normally as it can be driven faster.

So the power increase is matched by a comparitive or slightly better increase in braking ability, the suspension, wheels and tyres are uprated to match and even things like headlights and seating is improved to reflect the new capabilities.

Put simply this is not just an engine conversion but a complete car conversion.

Roger Parker

This thread was discussed between 08/11/2000 and 20/11/2000

MG MGB GT V8 Factory Originals Technical index

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