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Engine question None TR.


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I have been reading an article about a V8 engine rebuild and he has "offset ground the crankshaft" to gain a few more cubic inches.

 

from 351CI to 377CI.

 

I havent a clue what that means, would someone explain please.

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Thank you gentlemen, the man must be nuts! I had no idea that such a thing could be done.

 

Chris's emoji tells all.

Did it on my last 4 cylinder engine competing Pete on my last TR Register Overall championship winning season, we offset ground the big ends by .88 (of 1 mm) and used -60 thou (yes MINUS SIXTY) big end bearings (Massey Fergueson naturally) which included 20 races and practices, a stint (about an hour)6 hour relay race at Snetterton running on Weber 48s and Michelin TB tyres (allowed in the regs) and 93 laps of Snetterton (sponsor event at British Heart foundation) back on SUs, naturally at full race speed (we broke the class record carrying a passenger ! hairy).

The longer stroke achieved allows the piston to arrive fractionally earlier and after combustion the piston leaves fractionally later, gives fractionally better torque but complies with "standard crank material" requisite in the regs.

At the "refreshment" of the engine at the end of the year the crank was fine but the oversize big end bearings were starting to be squashed out of the sides of the conrod (the larger amount of the softer bearing material compressing and deforming). I just replaced with same size bearings.

Incidentally the crank when being prepared and Tuftrided (hardened) had bent by...gulp 10thou from the centre main to the crank nose. It was returned to the engineering company for straightening (they hit it with hammers... large hammers) and returned the crank without grinding it (it would compromise the hardening depth) straight...I mean straight ! no deviation on my DTI (clock) ...at all. I had to check the clock, I thought it was broken !

Car was sold with the refreshed engine and won the 1989 TR Register Championship with Chris Conoly driving it, I believe it carried on running on the ST crankshaft for some seasons.

 

Mick Richards

Edited by Motorsport Mickey
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Hi Pete,

to go with Bobs reply you could also offset the con rod small end bush but it has less effect.

 

Roger

Hello Roger

I do not think that would give a longer stroke just piston further up the bore!

Crankshaft gives stroke rod is just position!

Roger

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Hello Roger

I do not think that would give a longer stroke just piston further up the bore!

Crankshaft gives stroke rod is just position!

Roger

^+1 You still get the slight advantage as Roger says of early arrival and later departure from TDC but you don't get the "leverage" of the slightly longer lever of the offset ground big end offset.

 

Mick Richards

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Hello Roger

I do not think that would give a longer stroke just piston further up the bore!

Crankshaft gives stroke rod is just position!

Roger

Hi Roger,

yes, you are quite right. I was getting confused with getting the pistons aligned. The stroke is unaffected.

 

Roger

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Back in the early 1970s when the Honda 750cc 4cyl was the engine of choice for motorcycle racing, Endurance and drag racing, boring and stroking was the way to go. The 750 could easily be increased to just under 1000cc for that class and nearly 1100cc for drag racing. However it was only a year or two before the Kawasaki 900cc 4cyl arrived with its roller bearing crank which could be bored to 1100cc and the Honda was history.

A couple of pics from back in the day!

Chris

Honda on dcoe webers &. kawasaki with garret Turbo

post-3379-0-65034400-1515964375_thumb.jpgpost-3379-0-06874100-1515964386_thumb.jpg

Edited by potts4a
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Great information and enlightening, I wouldn't have thought Micks crank would survive such abuse.

 

Love the bike picks, saw a lovely Aprilia this afternoon I must go to the gym or find a time machine!

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