revtothelimit - motorbike forum

JackyJoll wrote: Sun Jul 13, 2025 5:20 pm P E Irving recommended a minimum 1/32” inlet valve seat width, although that’s for competition.



Are you familiar with three-angle valve seat cutting, to avoid making the radial flow change direction more than 15 degrees at a time, when the valve is open by a small amount?

Err no.

I do know i need to look for a copy of Tuning for Speed. I thought my Dad might have had a copy, but we haven't found it yet.

Try googling Tuning for Speed download. It is or was available as a free pdf here and there.

JackyJoll wrote: Sun Jul 13, 2025 5:50 pm Try googling Tuning for Speed download. It is or was available as a free pdf here and there.

Just had a look and Scribd has it.

AbeBooks also have hard copy versions for sale as well.

It’s worth a read.

It’s not all relevant and some advice may be obsolete, but he knew how to have success with a bike like yours.

JackyJoll wrote: Sun Jul 13, 2025 6:29 pm It’s worth a read.

It’s not all relevant and some advice may be obsolete, but he knew how to have success with a bike like yours.

Has to be said I'm not really building it as a proper race bike. I'm happy with reliability, but sometimes they do go hand in hand.

Racers have a lot of good ideas.

I think that should be usable now.

Decided to actually get into the workshop yesterday! (other things have been happening, or putting me off), and figured I'd have a tinker with the timing chest because I was advised to check the cam-wheel/cam-follower end play before I assembled the crank.

Firstly it took we a while to find the studs, then I realised that none of the threads were very clean, so gave them a good brass-brushing.


But even then it seemed that none of the studs would cleanly go into the case, and some of the nuts refused to go down the studs easily. So I ran taps and dies over everything (took me at least 20 minutes to actually figure out the thread form and find the right taps & dies, which I DID have amazingly: turns out it they're 1/4x26tpi BSF).





Eventually I managed to get everything spun down and tight.... then realised that one of the allen head cap bolts that are used inside the timing chain case was too long for it's hole! I can only imagine that Dad never noticed this bolt was the wrong length (nothing surprises me anymore...) so I cut them both down by about 5-6mm (well - the thickness of a nut) : I did both of them so I didn't have to faff with picking up the "correct" bolt for the shorter hole each bloody time.



So - eventually I got the case to tighten down on the timing chest.... and the camshaft is jammed.



The Cam-followers are rattling around on their shaft as well - there's at least a mm of movement, if not more.



But it's the camshaft being jammed that is confusing the hell out of me. The bushes that it sits in are open ended so it's not like the saft is running up against the end of a closed hole.

The timing chest case DID have a paper gasket fitted when I stripped it down.... so I'm currently thinking that "maybe" the thickness of the paper gasket is what is providing the end-play gap offset for the cam-shaft itself.

Photos from the strip-down: you can see the paper gasket clearly.





So - the next job, I guess, is to make up a new gasket and see if that frees off the camshaft, and look for a proper shim for the cam-followers. I did find a ~1.5mm thick washer that was exactly the right internal diamater (1/2") to fit the cam-follower shaft, but the cam-followers did get "tight" when fitted - so again - if the paper gasket provides the offset.... this might work...



Oh yeah - also - over the summer I got some repairs done on the rocker-box parts:








The oil-galleries need to be machined back down to approx 3mm high and a similar thickness.
See here :




TBH, I'm probably going to do this by just fitting a dremel-esque grinding tool into the piller drill and using it as an ersatz "single-axis machine-tool" and gently take the aluminium off flake by flake...

In addition the rocker arms themselves will be ground down to be narrower (and lighter), as previously mentioned.

Must be cool to work on the bike knowing your Dad's hands have been all over it.

Skub wrote: Wed Oct 22, 2025 7:57 pm Must be cool to work on the bike knowing your Dad's hands have been all over it.

Sometimes.....

Skub wrote: Wed Oct 22, 2025 7:57 pm Must be cool to work on the bike knowing your Dad's hands have been all over it.

If it had been my Dad half the bits would be missing and the rest would be held on with garden wire

Another afternoon in the workshop, step forwards, step backwards.

(Actually, this was a few days ago)
Stripped down the Concentric I bought, it's not a Premier (which has a removable Pilot Jet, where the original Concentric has a fixed size bushing, and drainable float-bowl).

It's "tired", which I expected, but all there and will make a reasonable back up if the Monoblock proves to be too much of a pain in the arse.
If I decide to try it, I'll probably invest in some updated components, gaskets, etc, and will give it a proper bzzzzzzzzzzzzzzzzzzzzzzzzzt.
The jets (at least) looks identical to the ones for the Monobloc, of which I have found quite a few in Dad's old bits so I can experiment with the main jetting at least (which is only really effective at full-bore.... )

Yesterday I had a go at making the gasket for the Timing Chest

Simple enough: the ball end of the hammer sheers the paper gasket on the hard edge of the facing with only gentle taps. These faces weren't really designed to have a gasket. Remember this is a race-engine designed for shale and grass-tracking with a total-loss oil system... weeping cases were a feature. Not great for the road or proper tracks though, so gasket making is something I feel I'm going to get lots of practise at.

Assembled up the cam-shaft and cam-followers again and its.... "better". the cam followers aren't sticking, but there's still resistance to movement from the cam-shaft itself. Stripped it down and smeared some R40 onto the cam-shaft and bushes and reassembled it
Liquid gold.....


That was an improvement, but still some stiction. So I stripped it again and smeared a lot more oil onto the camshaft, reassembled and just as I wsa tightening up the very last nut on it's stud.... FUCK. I felt the thread go. Tried the camsaft rotation while it was all assembled and it's a tad better, but I still think it's a little tight, so will order up some 0.8mm paper (the gasket paper I had was 0.4mm) and see if that makes the difference.

In the meantime... stripped it all down again carefully... and fucksticks.




"Luckily" it's the hole at 5-o-clock on the face, which means it's got plenty of wall, and it's a blind hole (so no chance of crap falling out the other end later).
Hit the TracyTools website and found a 1/4" BSF thread repair kit which will hopefully turn up next week (grabbed some Imperial sized drill bits too, seeing as I don't have any at all, the sort of thing I'm sure to need at some point). Also ordered some more gasket paper.

Hey ho, not really that much of a surprise, but still a tad irritating.

Would you not be better with Hylomar blue than gaskets?

Taipan wrote: Thu Oct 30, 2025 1:10 pm Would you not be better with Hylomar blue than gaskets?

Oh I'll be using that too!

But in this instance the gasket is giving me a needed bit of offset between the cases in order to prevent the camshaft being "pinched" between the main crankcase and the timing chest cover.

I recall back in my young,skint days making my own gaskets and finding out the hard way that it was best to use proper gasket paper,because cornflake packet cardboard is actually porous and falls apart when wet.

Skub wrote: Thu Oct 30, 2025 1:49 pm I recall back in my young,skint days making my own gaskets and finding out the hard way that it was best to use proper gasket paper,because cornflake packet cardboard is actually porous and falls apart when wet.

Funny you should say that... I've had great success with kellogs packet cardboard. In fact I think there was some cornflake packet on this engine wehn I stripped it....




My mistake - Rice Krispies!

Rockburner wrote: Thu Oct 30, 2025 2:17 pm Funny you should say that... I've had great success with kellogs packet cardboard. In fact I think there was some cornflake packet on this engine wehn I stripped it....


My mistake - Rice Krispies!

Ah,that's the ticket,then.

I use these for making the holes

https://www.ebay.co.uk/itm/286054314321 ... 4314321%3B

A quick bosh with a hammer nad - nice round hole.

Rockburner wrote: Thu Oct 30, 2025 2:17 pm

Skub wrote: Thu Oct 30, 2025 1:49 pm I recall back in my young,skint days making my own gaskets and finding out the hard way that it was best to use proper gasket paper,because cornflake packet cardboard is actually porous and falls apart when wet.

Funny you should say that... I've had great success with kellogs packet cardboard. In fact I think there was some cornflake packet on this engine wehn I stripped it....




My mistake - Rice Krispies!

I'm loving this thread for even more reasons now!

interesting looking hacksaw , is it old?