5K build help request

[altezzaclub]

We get two-piece gaskets as stock over here, and replace them with a one-piece. That has larger holes as I recall.

 

 

 

[Viterbo]

Was told 3K-B bigports have 30mm intakes and the maximum the head holds is 33mm and it's already taking a risk.

4Ks are 28mm and my head is already +2mm.

Maybe going 31 or 32?

[altezzaclub]

Ok, the 4K started at 28 and that one-piece gasket was about 4mm larger in diameter. So I took the ports out to 32mm at the entrance and let them taper back to normal along their length.

Its a black art.  I have access to a cracked head, but I don't have a way to slice it!

[Viterbo]

That helps a lot altezza, thank you!

Anything on the exhaust side?

[altezzaclub]

I just took it out to the gasket really, I was matching ports, gasket & manifolds. much to my horror I found the brand new extractors were not straight, so that idea fell over.

Seeing I was chasing cheap low-down power my mods were pretty simple, everything happens before 6000rpm & it never gets revved over 5000 really. If I was to work it up a bit I'd replace the inch & 1/4 SUs with bike carbs, maybe open the inlet ports out further along their length, and lean on Banjo to show me how to build a completely computerised ignition system.

The extractors & exhaust work fine, the light flywheel lets it rev quickly, and I'd try a hotter cam just to see the difference. With the extra cc you'll definately need bigger carbs and I'd have the 2" exhaust all the way through. Open the inlets up to where the valve guide comes through but just clean up the last part leading to the valve, especially leaving the floor curved as it goes to the valve. Exhausts not so crucial, so long as they match the extractors, & if you want them bigger I think they get taller rather than wider.  Oldskewltoy is the man to ask, I know nothing compared to him.

I'm a believer in the theory that there is a lot to gain from the ignition curve, and  a programmable ECU would make my advance curve mods look like child's play.

[Viterbo]

Need a few more hints on this build:

- I'm going to buy new lifters (3F ones). Is it worth buying new pushrods? (if they're available). I already have a few sets of used 4K pushrods, wondering if buying new ones is worth it.

- Been reading a lot about breaking in a new flat tappet camshaft. Mostly regarding V8s but I think K engines are also flat tappets? What do you advise doing to break in a newly built engine (rings, bearings, etc) with a regrounded camshaft and new lifters? This is what I think is correct - Make sure the engine will start right away. Carb full of fuel, oil circuit full using an electric screwdriver on the pump (or using the shaft of an old dizzy). Instantly rev it to around 2000rpm and let it bounce between 2000 and 3000 for around 20 minutes. Replace oil and filter after this. Then go make around 100kms applying little stress to the engine but letting it go down the rev range but itself to create vacuum so it seats the rings. Use an oil with a lot of zinc. Anything wrong until this point?

[7000rpm]

You should be ok with the used pushrods.

yes, they are flat tappets. Cam break in proceedure seems good. The reground cam should have a specific lube applied that the cam grinder sends you.

i ran mine for about 12 minutes at about 2000rpm, was all good