Hitchcocks Forum

Just thought I'd look in and say how I've been getting on with the Hitchcocks tuned head I fitted to my 350 bullet classic to replace the original one that dropped its valve seat.

All in all, it's made a big difference to the bike. In combination with the tuned samrat rockers it must have wiped a couple of ounces off the moving parts in the valvegear. The bike is noticeably quicker off the throttle and will pull through to higher revs. This has the major upside of allowing the bike to pull fairly well up to maybe 50mph in third making it not so much of an uphill struggle to hook fourth and get it purring along nicely at road speeds. The whole experience seems smoother.

To put some figures on it, I went along to the drag racing again at Kirkbride drag strip. My previous best had been 22.68s @ 58mph over a 1/4 mile sprint. This time round I managed 19.86s @ 63mph. The speedo was showing just under 60mph in third before the valves started to float and I had to hook fourth. My 30yd times were very similar to the last time out so it's all top-end gain.

Interestingly, I also noticed the pressure bypass valve working for the first time. By the time I'd done a few runs the oil was getting pretty thin and hot and I reckon the overrevving and abrupt gear changes meant the scavenge pump was working overtime as I finished each run and wound off. I could see a little oil seeping round the banjo on the bypass valve each time I came back down the strip. I've kept the o-rings in the samrat rockers so they are properly pressure-fed so it's nice to see the bypass valve is doing its job.

It's tempting to try a bigger carb on it to take full advantage of the tuned head but equally, it's running really sweetly on the standard mikcarb. I may try one of the several CV carbs I have lying about off various defunct Japanese machines, more to see what happens than anything (I suspect an almighty backfire and a torn diaphragm).

Hi there--------great piece of reading, especially as it co-incided with Steppen Wolf and Easy Rider theme being played on the screen of my PC. So----I have to say it }----it's wonderful what a good TUNE will do, ain't it ??????

I thought that the pressure relief/bypass assembly was designed to vent excess pressure when the oil was cold. This is when pressure is at its greatest. If the bypass is dumping oil into the crankcase, rather than going to the rockers, when the oil is hot, then the opportunity of getting more oil to the top end to assist cooling under 'arduous' conditions is being missed.
I would remove the 'o' rings from the samrat rockers and let more oil get up there. You don't want maximum pressure in the scavenge system, just plenty of oil flow.

Hi to Another Allan. The O ring in the Samrats is fitted on the oil way from the bottom block to the top block, it does not reduce the flow rate though the rocker block in any way. Wheter it is required is debateable, it does no harm but it doesn't do much good either. What restricts the flow is the size of the hole that runs through them and the excellent fit of the rocker shaft in the alloy castings. There is a Tech feature as regards the size of the hole. Most owners drill out the oilway to about 2.5mm, I also drill right through the top cover with 2mm hole to prevent over pressurising the scavenge return flow. As Stickwheels' bike has the scavenge OPRV then the mods are not really necessary, but won't do any harm either, apart from the possibilty of over oiling the head with the increase flow. The Indian models should have an oil seal at least on the inlet valve guide to combat the full oil flow to the head which the original engine was not designed to cope with or require. Dowty seals on the oil feed banjos should help seal the leaks.

Hi LES H ---------- could you just expand on that " I drill right through the top cover " idea please ?? How does the scavenge return flow become pressurised if it's a gravity system from the head dowmwards ? AH-----are you referring to a bike with that return Valve fitted, perhaps ?? Yes, I agree about the stem seals---especially on the inlet stem. I recently tried using some seals on my Classic 500 during it's head overhaul-----they don't fit !! I tried 2 sets, plus a call to our hosts for some help. But despite all that, plus others saying "Oh, you have to machine some metal off the stem ----------- " (Oh yeah !!) they still didn't fit. That was £20 down the drain. (GLUM BUNNY !!) I'm about to give bike No2's head a top-end session so will try a different approach ie Taking the dud items over to "Cloisters del la Chadwick-End" and get them to sort it out. Catch you later-----------

The seals fit fine on the new bronze guides but not on the original iron ones. I found the top edge to sharp to get the seal over and also spent several hard earned dollars on bits of shredded green rubber.

I always understood the scavenge to be what is picked up from the sump (having passed through the mains) and fed to the top end through the external oilway. With the samrat rockers, the oil only has a small hole to pass out through having been pumped into the rocker block, they work a bit like a plain bearing in that respect. If the scavenge pump has picked up a lot of oil and tries to pump it out through a small hole, you're going to generate a lot of pressure in the system and put excessive load on the pump.

There are two solutions. One is to make it easier for the oil to get out of the rockers by enlarging the hole, omitting the o-ring and drilling an additional hole in the top rocker block. Essentially making them deliberately leaky. The other is to fit a bypass valve in that oil line so if the pressure becomes excessive, it is bled off and returned directly to the timeing chest without having passed through the rocker blocks.

Given how I've been having problems with excessive oil flow to the top-end overwhelming the valve guides and leading to burning of oil, it made sense to keep the rockers in their original trim and leave the bypass valve to deal with any overpressure scenarios (which are only brief in any case, usually on the overrun from high rev speeds where the scavenge pump has a lot of oil to pick up).

Hi SIMON---------- this WAS onto new, bronze guides !! Alas I had already fitted the guides into the head WITHOUT trying them on loose first. YES, I know--after 40 odd years of doing this sort of thing I should have known better and done a dry run first. With No.2 bike I shall be poised and ready to POUNCE !!! Grrr.

When I built my crossbred motor I opened up the slots on the end of the rocker blocks to allow any excess oil ( I was unsure how much increased volume the gear pumps would push up there) to get out and drop down the pushrod tubes. I also fitted an oil pressure gauge to the rocker feed and on initial start it would pump 30 psi untill it cleared the oil in the sump.I also thought this was flooding the head with oil, but I couldn't prove it for sure. This oil problem was made worse by the fact that the Electra doesn't have an oil seal on the timing side shaft and oil was either being dumped into the sump from the timing shaft or from it working its way through the gear pumps. I fitted a brass hand pump to the front sump plug and each time before start up after it has been sitting for a while, I just give it a few pumps to clear the oil down there and start it up with no problems. Always gets a laugh when people see the pump, but it works

NORM !!! That's known to me as a BILGE PUMP and at our time of life ANYTHING that helps get you started is OK by me !! (Know what I mean, Squire ? Nudge-nudge, wink-wink !).Say no more !!