750 Head on 850 Barrel

Fast Eddie said:

I have. I’ve done it !

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When we were clearing out your namesakes workshop we binned about 15 sets, both Unit (which had been beefed up) and proper Nourish/Weslake ones. It was about one set per season

Never heard of an 8 valver that was slower than a 2 valve one either... provided they were assembled properly and the cam timing modified..... but, you know who "knows better"

Rod Tingate is very experienced . He worked for Colin Seeley and was in UK with Kim Newcombe and the Konig when Kim was killed. His race bike in the 60s was a 650 Triumph twin. He fitted a Rickman 8 - valve head to it - made no detectable difference. He might not have experimented much to get the best out of the modification. But the head was not just bolt-on power. With Jawa speedway motors, a good 2 valve is almost as quick as the average 4-valve.
When Steve Ozsko was racing his 2 valve Mamx against Ron Toomhs who was riding the Henderson 4 valve G50, The G50 was very slightly faster. The Mamx could hold it, but not pass it. The G50 even had magnesium pistons. I watched those two bikes out in front of A grade fields in many races. All Steve could do was wait for Ron to make a mistake. Ron never made mistakes except the one which killed him at Bathurst.
With my own Seeley 850, my problem was I did not suspect until too late, how to use it properly. It is very different from most other race bikes.
A while back I mentioned a close ratio gearbox helps a bike to accelerate faster. There were some doubters. That in itself tells me something.
When you lose revs on upchanges with the heavy crank, you do not have the throttle response to get them back quickly. With a close box the gaps between the gears are smaller and the revs do not drop as far. So you are not so dependent in throttle response.

As you say, an 8 valve head is not just bolt on power.
It requires setting up.
It gives the opportunity for much bigger ports and carbs. For much higher CR. For dedicated cam and exhaust set up. Etc.
Of course a well set up 4 valve will trounce a poorly set up 8 valve. But that’s about it.

Fast Eddie said:

As you say, an 8 valve head is not just bolt on power.
It requires setting up.
It gives the opportunity for much bigger ports and carbs. For much higher CR. For dedicated cam and exhaust set up. Etc.
Of course a well set up 4 valve will trounce a poorly set up 8 valve. But that’s about it.

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Tye original instructions with the 686 kit specified the valve timing changes, it wasn't a straight bolt on kit. If I remember correctly, the angle of the cam followers is different with the 8 valve kits

Seeley920 said:

Tye original instructions with the 686 kit specified the valve timing changes, it wasn't a straight bolt on kit. If I remember correctly, the angle of the cam followers is different with the 8 valve kits

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Did you have to machine the inside of the pistons to fit the rods ?

Seeley920 said:

If I remember correctly, the angle of the cam followers is different with the 8 valve kits

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Yes, correct, the cases have to be relieved accordingly.

baz said:

Did you have to machine the inside of the pistons to fit the rods ?

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It's 40 years since I had the damned thing. I had been a Triumph fan til then. Never again.

I can't remember having to do anything to the rods, but I have formatted 99% of Triumph knowledge from my brain

Seeley920 said:

It's 40 years since I had the damned thing. I had been a Triumph fan til then. Never again.

I can't remember having to do anything to the rods, but I have formatted 99% of Triumph knowledge from my brain

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No it wasn't to the rods
It was to the inside of the pistons
More than one person has told me that the inside of the pistons were designed to be finally machined by the customer to suit his rods
But a lot of people just went ahead ignoring the instructions and just bolted the whole lot straight on?

baz said:

No it wasn't to the rods
It was to the inside of the pistons
More than one person has told me that the inside of the pistons were designed to be finally machined by the customer to suit his rods
But a lot of people just went ahead ignoring the instructions and just bolted the whole lot straight on?

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Well, this was one of the original Rickman kits, so no machining necessary. I'm not sure about the Nourish ones, but I would have thought if you specified what you were going to use, Dave would have supplied them to fit

Some big Nourish engines had wider bore spacing than Triumph, so some folk got caught out when mixing n matching parts.