Yes, that's a reasonable rule of thumb. It comes from the crossover between intake flow being restricted by the opening around the edge of the valve, the curtain area (~lift x valve seat diameter x pi), and the flow being limited by the port area (~ pi x port diameter). Ignoring the fact that the port diameter is usually smaller than the valve head, and the valve seat is a little smaller than the valve head, the crossover in flow restriction occurs when the lift, L, is about 1/4 of the valve diameter, D. But, you want to keep the valve open as long as possible to get the maximum total flow and as you can't stop the valve at L=0.25D, you end up running it a bit higher to slow the valve down and get it to start closing; so the maximum lift ends up around 1/3D. All of that is for normal road engines, with racing engines they play tricks with the dynamics of the intake flow and the valve event ends up being a bit more complicated.
I asked what the rocker ratio was because I’m curious. A cam grind between an Engle 100 and 110 should work with either standard or 1.25:1 rockers but where the power is developed in the rev range will change. For a bus engine standard rockers would probably be better, although if PanZer wants to continue driving at the speeds he has previously maybe making more power at high revs is preferable. I wouldn’t trust any engine builder. Maybe, just one.
Previously there wasn’t a huge amount of power at higher revs (but i’ve no Bay experience to reference), but enough you could get ahead in advance of something fast coming up behind (i’m motorbike mirror checker) and pull in out their way on a dual carriageway - if you found yourself needing (which is just wanting) to get in front of someone doing 5mph below the limit. 4,200rpm was the highest I revved in 4th - belt slipping range hey. But more on that next week. Interestingly the PO told me to hold it at 5,000rpm to get it started - belt breaking range. The builder never got to see it working prior to seizing so relied on anything I could relay to him. Overall he said it would be comparable as a rebuild, but because he made changes he felt would improve it overall, i’d gain more low end power at the expense of top end. Sent from my iPhone using Tapatalk
Is that what you had to do? What changes has the builder actually made? Different heads and cam I think, but without knowing what was fitted originally, it’s difficult to say how it will compare.
It’s been so long since I used it, but from memory, yes! A minute or so with a very loud exhaust. Then i’d step it down 500rpm until my alternator temp gauge was about 30• and then it seemed to idle fine. I’m usually up very early so that was mostly cold starts. Warmed up it wasn’t like that. I know I must have been doing a lot wrong back then. Deck Height changed from 3mm to 1.5mm. Compression Ratio changed from 7.3:1 to 8.5:1 Crankshaft changed Valve sizes changed Camshaft and followers Carburettors will now take Vacuum Advance He would have done other things I don’t know about. For instance, we never talked about Rockers, so that was a new term to me. But since it wasn’t itemised he would have reused what was there. The engine was previously rebuilt with only 1,000 miles on it, when I bought the Bay. I put another 3,000 on the clock. Sent from my iPhone using Tapatalk
I did have 5700 RPM sitting on the peak display on my rev counter on a 1641 after flooring it in second at around 37 mph going down hill onto a motorway... Nothing broke for the few seconds it was running that fast before I changed up to third. Stock belt, fan, pulleys etc.
@PanZer If you are keen on getting to know your engine better, here is a link to a good read: https://www.thesamba.com/vw/archives/manuals/jim_martin_engine_build.php Jim Martin Engine Build - its a pdf which will sit on your iPad for a leisurely read!
You didn’t misunderstand. When cold. I feel on the verge of a telling off. These are my notes on starting: •Key turns forward •Keep forward until fired up •Feather Fuel until warm (tapping accelerator) •Get it steady at 3000rpm (this is what I think took up to 5,000rpm to get it firing on all 4 cylinders...but I never knew what that sounded like as it was just loud!) •Idles at 1000rpm He made me do it! Sent from my iPhone using Tapatalk
When you get it going again... don't do that. A bit of pedal action will get it firing on all 4 without allowing the revs to rise much above 2,000rpm but try and keep it as low as you can short of stalling is the aim because high revs/cold engine is not best.
Didn’t you find it unusual that you had to rev the nuts off it to get it running? You shouldn’t leave an engine idling before driving off but you shouldn’t use maximum revs either.
I won’t. This time around i’ll have a mechanic with me to give proper instruction and orientation. He has offered to drive it in too, to be sure I don’t do anything silly during that process. Sent from my iPhone using Tapatalk
I did, but i’d never even seen an aircooled engine before so assumed that was normal. Unfortunately the PO sold himself as being very knowledgeable about machines, so I willingly just did what I was told. I was never told otherwise either. It did take quite a bit to warm up, but after that was fine. I never knew that about leaving the engine idling either. Thanks The maximum revs were 6,400. Since I was quite a lot below that, it didn’t feel like I was killing it. Sent from my iPhone using Tapatalk
Mine sounded scary when I had trouble with the choke on my progressive being loose meaning the cold idle endstop was disabled. But looking at the rev counter it only ever went to about 2000 rpm peak with my foot on the throttle. So it had choke but no cold idle throttle endstop to speed the idle (equivalent to around 1500 rpm if warmed up but 800 when cold) instead it just about wobbled along at 500 rpm. Its not good thrashing a cold engine as there is that bit where the oil pressure is still low and the bearings may touch . Or leaving it idling to warm up as so many do when they keep their buses off the road over winter, as the wear on the bearings is noticeable. Engine builders over on the Samba report that they can spot the engine that was idled periodically to warm up by the wear patterns on bearing shells. Maybe Muir was about right. Start it, make a roll-up then drive off..
Theres a reason why Americans fit Kadrons (Solex 40s) and Europeans dont. Good marketing ..not necessarily an appropriate product.. a bit big for a low revving bus.
I was going to ask if you knew how to break in the new cam and then get the piston rings to seal, but hopefully you have someone that knows what they are doing.
Yes, hearing mixed reports about Kadrons. Mainly the Americans who love them. The engine did come from California. Hence no thermostat too maybe. I was told mine was chokeless. Well, certainly no choke to pull out. Gosh, I’m realising how little I actually remember - second guessing myself on a few things. It’s been a whirlwind few years. I’m relying on notes I make - which I do fairly prolifically and reasonably accurately. I do like to know how things work, but honestly, the engine was last on the list for me to learn about. It was new, worked (as far as I could tell), the most intimidatingly complex and there were dozens of other completely new things I had to research. All thanks to TLB and Google i’m getting there. Sent from my iPhone using Tapatalk
