61 replies to this topic

[Lee Nicolle]

Having looked at rules in the CAMS manual some classes allow + 1%. I believe this to be for eg an engine near capacity that is honed say 1 thou bigger for extra piston clearance. Many production based engines need more clearance or you scuff the skirts badly. 

As far as I am concerned there is no way a standard production car engine will live safely on road car clearances without damage.

Piston to bore often needs to be doubled say 2'5 compared with 1 or even .08, crankshaft  oil clearances checked and sometimes doubled, 1 thou to 2.5 thou or even with synthetic oil 1.8-2 thou. Very occasionally lifter bore and cam tunnel clearances as well.

Cam tunnels are a real pain, both OHC or OHV when you fit new bearings they on occasion have to be line bored. I have seen engines with low oil pressure that have hammered the cam bearings. OHC can be a bigger problem as there is no bearings, if and when the head bends you are sometimes forced to bin the head, it may well run bent but something will give eventually, either the journals fail of the cam breaks. I have seen both. The harmonics from a camshaft is generally  horrendous. 

This only applies to engines being raced when fresh, turned to maximum rev limit lap after lap. For road use the standard clearances are fine as the engine should be 'run in' and it all settles down to useable clearances and even after the initial period is seldom ever turned to max rpm.

[SJ Lambert]

Good question, let's analyse...

The first suggestions I heard of this sort of thing were from BRM mechanics referring to Jack and Denny in their Repco V8-powered cars in 1967.

The 'power circuits' where one would expect the most advantage from an oversize engine were Sandown and Longford. Brabham had pole there with a 1:05.7, but Stewart was only two tenths slower and quicker than Hulme's 1:06.6 and Clark with 1:07.7. Engines for Stewart and Clark were both 1.5-litre V8s stretched, Steweart's at 2.15-litres as I recall, Clark's at 2-litres.

To my way of thinking, those times would be exactly what I'd expect of those engines, so what about race day? On the tenth lap Stewart passed Brabham for the lead and had fastest lap of the race so far at 1:06.9. Brabham then had a wire fall off the ignition pickup on the flywheel, located this out on the circuit and pitted to fix it properly. Hulme, meanwhile, did a bit of to-and-fro stuff with Clark before retiring. Though Clark passed him coming onto the main straight, Hulme had to use Clark's tow to repass the Lotus up the back straight.

And Jack? He came back to do another 18 laps or so, his only result from this (apart from flying the Repco flag in front of the Company's directors) would be to get fastest lap and/or the lap record. His best, however, merely equalled Steweart.

Longford saw Jack take a win, but again the times were close. Brabham and Stewart, in fact, equal fastest on 2:13.4. Grid postions, however rested on lap times in the Examiner Trophy race over eight laps and another eight-lapper, pole went to Brabham and 2:14.5, Hulme 2:14.8, Clark 2:15.0, Stewart 2:15.2. Do we question Clark's climax's capacity with that? In the race it seems Jack was doing it fairly easily, Stewart got down to 2:13.9 in his pursuit and Jack did a 2:13.3.

You could say Jack was playing with them there, but two things go against that thought. First, he and Denny went out together in practice, undoubtedly to help each other with some slipstreaming, and still Jack did only the same time as Stewart - and remember that there was a hundred bottles of bubbly riding on this. Second, it was not until the second eight-lapper that he was fast enough to get pole for the main race.

So we go on to 1968 when the Brabham mechanics were complaining about the DFVs...

At Sandown Jack had pole with 1:06.7 to Clark's 1:06.9 with Amon's Ferrari in the middle on with 1:06.8. There would be no doubt about Geoghegan's 2.5-litre integrity, he was fourth fastest on 1:07.0 in the old Lotus 39 ahead of Hill's 49 on 1:07.3.

Race day saw that storming race from Amon and Clark where they diced throughout and Clark only just managed a win. Amon got fastest lap with 1:07.0 to Clark's 1:07.2.

The little Dino V6 was definitely not 3-litres or anything near it. It was stretched from 1.5 or 1.6 or something and it was scratching to be 2.46-litres because of the need to move head studs to places where they were in the way of the valve springs!

At Longford Clark was clearly quicker with 2:13.0, Hill on 2:13.1 and Amon on 2:13.7. Not a huge advantage on a circuit like Longford where the Cosworths were fully expected to dominate.

Further to that, the next year Amon was able to beat Rindt regularly.

As for the BRMs, which are the other cars which could have gone with 3-litres with their V12s in 1968 and 1969, I'm sure Doug has fuller information.

 

Another one of Tom Thompson's shots 

 

 

[E1pix]

Cool image!

[SJ Lambert]

Here’s Pedro’s 2.5 litre B.R.M. through Tom’s lens from the same meeting

[E1pix]

Hey, that's not Pedro! (LOL)

Awesome shots!

[Henk Vasmel]

Hey, that's not Pedro! (LOL)

Awesome shots!

How do you know. The car clearly shows P.  Rodriguz, and I don't know what he looks like. Must have been confusing for BRM though, two drivers with very similar names.

[opplock]

How do you know. The car clearly shows P.  Rodriguz, and I don't know what he looks like. Must have been confusing for BRM though, two drivers with very similar names.

 

Perhaps DCN can identify the dyslexic BRM mechanic. The spelling was right on the car I saw at Levin and at Warwick Farm from photos I've seen. They did have to swap between V8s and V12s a lot so probably had to do some rush jobs on the signage. 

[Michael Ferner]

Didn't they once employ a dyslexic driver, too?



"Ahh, this Stewart boy sucks at everything! He's no use as a mechanic, can't do signwriting, and frets about the broom when he's told to sweep the shop floor! About the only thing we haven't let him do is drive the darn racing cars..."

Edited by Michael Ferner, 04 December 2017 - 23:05.

[E1pix]

How do you know. The car clearly shows P.  Rodriguz, and I don't know what he looks like. Must have been confusing for BRM though, two drivers with very similar names.

Ha, well at least one of the Pedros looks *nothing* like that! ;-)

[SJ Lambert]

Looks like the signage man may have been somewhat left hemisphere dominated!!!

 

 

 

 

[Glengavel]

Didn't they once employ a dyslexic driver, too?



"Ahh, this Stewart boy sucks at everything! He's no use as a mechanic, can't do signwriting, and frets about the broom when he's told to sweep the shop floor! About the only thing we haven't let him do is drive the darn racing cars..."

 

Well, he did work at the family garage as a mechanic.

[SJ Lambert]

Just on the notion of the Repco Brabham engine capacity variants.

 

The 2.5 litre engines such as the '67 type 640, 740 & 830 were  nominally 84.83 x 55.0 for 2488cc

(3.34" x 2.165").

 

The 3.0 litre F1 versions such as the 620, 640 & 740 were bore & stroke of 88.9 x 60.325 for 2997cc

(3.5" x 2.37").

 

I imagine that a simple dowel test could possibly reveal a long stroke motor on any given weekend.