Tag Archives: porting

The head question

I’ve been trying to work out what to do regarding the Triumph cylinder head. I’ve not built this engine up as a 500 for years and it’s not really a ‘bolt together’ job as it is.
I started racing it in 1988 and at that point it had the bronze head. It was the first geared bike I’d ever ridden and the first time I rode it was at a Cadwell park practice day. I remember seeing these RC30s screaming by me at every corner of the track. It was dangerous of course as novices (and especially ones that can only just ride a bike) are completely unpredictable. I survived though.
After my first season, we stripped it and realised that the valve seats were quite sunken by many years of use (no seats.. straight on the bronze)IMAG0522 so we asked Owen Greenwood in Loughborough to have the bronze head seats built up ready for re-working and in the meantime I ported an iron head for that season. I obviously enjoyed using the air grinder as I definitely took enough metal out(!). In one place the seat is thin enough that I worried about overheating. No multi angles, no finesse! IMAG0516 We ran that head for another season or two and then it didn’t get run again until I rebuilt it to take to the Beezumph in 2001. I should have left it alone but I was obviously seized by the desire to improve it. This seemed to involve skimming 0.080″ of the head and the barrel spigot in order to increase the compression ratio.Doing this causes all kinds of issues as you have to deal with the sealing of the pushrod tubes and the lengths of the pushrods. IMAG0517It was misplaced endeavour, but it probably was fun at the time. Unfortunately There wasn’t enough clearance and the substantial 1.5″ inlet valves (Norton Atlas if you’re interested) contacted the pistons. It didn’t result in carnage, but we knew that it wasn’t really running right so I only did a couple of sessions.
I didn’t start racing with the VMCC again until around 2008-ish, twenty years after I first raced with the club, and this time it was with the Scott, but the following year we rebuilt the Triumph with the big motor (680cc) so the 500 has lain unused and unresolved.
I think considering that if I had no other options I’d be justified in re-working the skimmed head, but I think I’d keep my life as easy as I can. It’s not like I have a lot of time, so I think I’ll stick to either re-doing the bronze head or an iron one. Time to get some prices for hemisphere recutting!

Roger on the Triumph  with 680cc motor in mid 1970's rounding Mansfield corner at Cadwell Park
Roger on the Triumph with 680cc motor in mid 1970’s rounding Mansfield corner at Cadwell Park

Richard at the September Cadwell meeting in 2008 (or 2009?) on the Triumph. 680cc motor fitted.
Richard at the September Cadwell meeting in 2008 (or 2009?) on the Triumph. 680cc motor fitted.

Triumph cylinder head

I’ve decided to rebuild the Triumph this year, after being working engine-less since the last BHR Cadwell meeting in 2009 I think), when the 680cc motor blew the RH cylinder apart just above the base flange at the end of the start/finish line straight at Cadwell, just as I was going into Coppice. Fortunately, being used to a two stroke, I’m pretty quick on the clutch and I just pulled off.
The 680cc motor is very exciting in the Triumph, as it does make it bend in the middle a bit and that trait is at the heart of more than one story.
Although I’d probably prefer to keep the big motor in it, a change to classes in the BHR racing has meant that the old vintage class (up to 1934) has been joined to the post vintage class (up to 1948). The grids numbers became too low to run them separately. This meant that whilst before you could get two rides in the vintage with the Scott and two in the post vintage with the Triumph, I have only the ‘up to 48’ class and the ‘unlimited up to ’63 class’ that I can ride with either.
I thought since I can do those four with the same bike, it would be nice to have the Triumph running as a 500 to run in a separate class.
I’ve got a 500 iron head that I over-enthusiastically ported when I was about 15 years old and then later (over)skimmed to increase the compression. It’s an example in iron of what not to do if trying to make a bike go faster. I could possibly recover it, but I do actually have an unmolested one and it may be the wisest thing to start again with a bit more care.

Me and Triumph at Beezumph 2009
Me and Triumph at Beezumph 2009