New member hello & APD rebuild

[John Cornforth]

Hi

Having recently done an engine rebuild, here are my top tips:

+1 for slipper pistons, noticeably reduced friction and slightly lighter
+1 for balancing rods at both ends
I used cap head 12.9 grade screws for the little ends, with red loctite. Gudgeon pins must be free in cold pistons, a little "working" may be needed with thin lubricant to take off microscopic high spots.
+1 for at least statically balancing the heavy flywheel / clutch. I didn't bother with the crank.
I used new standard valve springs, which seem fine to 4500 RPM but I rarely go above 4000.
+1 for silicone base gasket (and sump gasket)
A high compression head will increase top end power, but won't be as smooth with only 2 bearings. It can be left as a later mod if desired.
Ignition timing is reliant on multiple pairs of gears all with backlash. Minimise this if you can, even dynamo end float can cause timing scatter.
I didn't modify the oil system, I just use modern oil which is vastly better than anything in the 1930's and change it regularly.
I did the front cam bush mod with a cap head screw tapped into the bush to hold it tight. I didn't add O rings as it was snug in the crankcase.

[Jamie]

I have mildly tweaked my engine, too. It has:

• High compression head
  
• 1 1/4" SU
  
• John Barlow inlet manifold
  
• Bunch of bananas exhaust manifold
  
• Rebore and new pistons
  
• Balanced crank and flywheel assembly
  
• Smoothed ports
  
• Lightly modified cam
  
• Shortened valve guides
  
• Flattened followers
  
• Over-bored oil pump
  
• A sprinkle of fairy dust
  

Frustratingly, I was not there when it was tested, but I gather that is very smooth and produces about 21bhp.

Jamie.

[Steve Jones]

All good advice but if you don't properly crack test your crank and rods first, it could all be a waste of time and money. Sadly, given them a good looking at and finding nothing isn't sufficient and it isn't only at the No. 4 journal that these cranks break. Looking at your photos, I'd be very suspicious of the knurling to the rear main journal and is that brazing at the same location? Also, as a matter of course, I'd replace the rear main bearing.

Edited to add: I agree with Alan, below in respect of using a new crank. Might seem expensive now but likely to be cheaper, and easier, in the long run.

Steve

[Alan]

Steve is right. Actually, these days, I don’t think I’d rebuild an engine without a new crank.

[`Gordonhbm]

Looking at the comments by John, Jamie, Steve and Alan above makes me wonder whether it would be advisable to go for new con rods to give peace of mind with using the full potential of the tuning.  I note the comments about cylinder heads and would refer you to Malcolm Parker's comments in https://www.austinsevenfriends.co.uk/for...nder+heads.
If you were using new rods should you go for white metal or shells for the big ends?

[Goldnrust]

Thanks everyone for all the helpful input.

I was quietly hoping that, as no-one had mentioned the crank till just now, it meant for the level of tuning I was looking at the crank  would be ok! But deep down I had a feeling it would be taking a risk.

I would love to be able call one of the trusted suppliers tomorrow and order myself a crank, but on top of the costs of pistons, rebore, balancing work, etc it's going to be beyond my current budget. I could wait and save up, but I wouldn't be driving the car this year which would be a shame.

With that in mind, I wonder if I'm better to go back to the idea of simply cleaning this engine up and throwing it back together in stock form, with some gaskets and a light hone, maybe the 37 head?, and that way I can get a few miles under my belt this summer.

If I'm enjoying myself, I can then maybe look out for a spare engine to rebuild and tune 'properly' in the future.

[Howard Wright]

Hi Goldnrust

I hung back on suggesting a new crank cos I knew how much they cost!……but two of my three cars have new cranks even though there was a lot of economic pain. My RK has an Austin crank but I had it professionally crack tested before I went ahead with the build. IMHO at the very least have your crank tested, no matter what you do to the engine.

Cheers

Howard

[Hugh Barnes]

And the rods - they can crack from the groove below the little end clamp bolt. I don't have a photo to hand and don't want to scrape one from the internet that doesn't belong to me. Perhaps some kind soul could post a suitable photo demonstrating the point?

[Robert Leigh]

I had the problem Hugh describes, after a, new when installed by me, HT little end bolt lost its head.

[Jamie]

I had my crankshaft, a three-bearing version, crack tested first, but the conrods had a visual and a "ringing" test only. Even if they had have been available, a new crankshaft would have been completely out of the question due to the cost. Crack testing the con rods also started to fall into that category.

Jamie.