Simes' FH Rebuild

[simon.holyfield]

Camshaft. Might be the least worn bit in the engine.

[nevhunter]

Your oil is not doing the job when the cam followers scuff out like that. They are the part of the engine highest loaded, and there really is a lot of sludge about. Nev

[Simon.Gardiner]

Ooooh - usual worn cam followers and I think I see a little ridge on the top of that cam lobe. Replace the lot and use an SRM cam 'cos they make them from properly hard stuff, not the cheese that other people (including OEM) seem to use. (SRM used to do followers as well but I've not seen them on their site for a while - you could always get your old ones stellite-tipped and reground.)
(Nev, these all look like that after a while regardless of how clean your oil is - Steve C. is only getting such high mileages 'cos his engine has SRM bits in it )
There's no problem putting the small bearing crank in the later cases, and I'm sure your big-ends will be fine once they are assembled with the shells in place (Sorry!)
I think I'd probably be hoping that the least worn part of the engine was the cam bushes...

SG

[simon.holyfield]

You're right about the ridge on the cam, but the cam in my Mk1 is much worse than that.

Just to round off the Ariel comedy nite - what do you all think of my 2.82" bores?

[simon.holyfield]

General views of the dynamo drive, oil pump and auto advance unit. Enough excitement for one day.

[simon.holyfield]

And I guess the last question is, what spec do I build the engine to? If the camshaft is too worn to use, and I have to rebore with new pistons then I can go to 7.25:1 with a hotter cam...

Thoughts?

[david.anderson]

Simes
It appears that you have a lot of work ahead. It certainly pays to use quality oil, a good filter and to do regular oil changes.
The A10 responds very well to the spitfire cam, which also works well at 9 to 1. The head will be the limiting factor performance wise. And Roland Pike mentioned that the Huntmaster was down on horsepower on the A10 when tested on the BSA dyno due to the over large exhaust pipes fitted by Ariel. Smaller pipes immediately resulted in a hp gain.
Is that oil pump a mazac one. If so I would be fitting a new SRM oil pump, which is also higher volume.
David

[pete.collings]

I have found that with a small journal crank and the thinner barrel flange on a Huntmaster, a combination of the 67-356 rocket cam and 7.25cr flat top pistons give the best combination of performance, tractability and reliability. An oil filter is a must, the sludge trap in the small journal crank is small, needless to say removing the trap plugs and a thorough cleanout is needed before reassembly. I have used an impact driver and bit ground to be a good fit in the plug slot to be the best way to remove them. The process will often damage the plugs, but be careful that any new plugs do not obstruct the oil inflow hole in the crank, if necessary file a groove in the correct position on the plug.

With the one piece crank (with larger journals) and the thicker barrel flange on the later A10 barrels, you can use a higher performance cam and higher CR ratio pistons.

[Simon.Gardiner]

Simes:
It seems that your current pistons+bores might be fine, but you're max oversize already so any change will need a resleeve unless you find replacement barrels. You'll find it very difficult to get dished-top pistons, they're mostly flat-top (or domed) these days, so availability will probably govern the choice of compression ratio.
I'd echo the advice above, if you start using 9:1 pistons with a thin-flange barrel (as all Huntmasters are ) you'll risk cracking the flange and anyway for longevity the small-bearing crank is considered best keeping to 7.25:1 and a 356 cam. Which also works well (and bear in mind that these things can vibrate viciously in the 'right' circumstances).
Your current cam is almost certainly the slowest 67-334 (I think Ariel carried on with it as 'standard' well after the A10 went to the 556), the 'spitfire' cam David refers to is the 67-357 profile as used in the late 'sports' BSAs (Rocket Gold Star etc).
The mazak bodies on the oil pumps distort (as well as getting worn). I think some have CI (or steel?) bodies. Check out Drags for replacement parts, they might also do a pump recon service which I've seen favourable reported on elsewhere. The SRM pumps are exceptional and seem to work well (as per Steve Carter!), but they are pricey.
You'll have noticed you've got alloy con-rods....but then, you've probably already sorted out your opinions on those from your time with the Square ....

SG

[simon.holyfield]

Thanks for the guidance guys. Unfortunately, today is a work day so no workshop time, but it's good to start thinking about options. I've been looking around for machine shops, since my favourite one closed a while back. Happy to hear your experience once again.
If I get any time, I'll measure up the barrel and pistons so we can think about what to do there. I'll spend money on the bottom end if the pistons and barrel are in any way usable - it's much easier to rebore/reline a barrel as a short term off-road job than rebuild the whole bottom end.

Good information on the cams - I'd seen the (BSA?) part numbers mentioned on the A7/A10 forum, so it's good to know what those mean. Parts seem to be quite easily obtainable from SRM and Feked, at a price.

At first glance, the oil pump body looks like steel or iron, but I have done no more than take a picture of it. I need to read up my A7/A10 Haynes manual before I go any further.

The alloy rods will be staying unless there is some crack or bend.

For now though, I have two work trips this week which will give me 8 hours sitting on trains thinking about the next steps...