Any interest in another Amazonian rescue? Head off

[Mr Pastry]

Piston to bore clearance has to be measured with the rings off, and on the thrust side with the piston (typically) 1"  below TDC.  This to avoid potential upper bore wear and because the piston is a complex shape.  If you have just put a feeler gauge between piston crown and bore above the top ring then  .020" doesn't sound unreasonable, but it doesn't tell you very much either.

[Ronkey]

I have got my head around this now I think . The 85.155mm dimension corresponds to the bore diameter for the +0.040" oversize pistons and I have checked all bores at the top and get this value. I have also borrowed a bore gauge and it varies by a maximum of 0.10mm in any of the cylinders (prob less tbh). Given the limit before a rebore is 0.010", or 0.25mm, then it looks like I am on a good wicket.  This was backed up further when I got the engine out and took the gearbox off. I was expecting the worst because there has been a steady drop of oil. On removal that is definitely coming from the gearbox so new seals required. It is filthy!

I got greeted by this:

And I didn't clean any of this! @juular , @warninglight and other amazon sniffers- what do you make of this? Is that a standard rear seal? Looks very advanced for 60yrs old. 

[juular]

  On 11/03/2025 at 23:10, Ronkey said:

And I didn't clean any of this! @juular , @warninglight and other amazon sniffers- what do you make of this? Is that a standard rear seal? Looks very advanced for 60yrs old. 

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That's an upgraded housing with a neoprene seal. Good news in my opinion as the original felt seals tended to slowly drip.

[warninglight]

Yes that seal is good news, I expect you have the same type behind the crank pulley too - I had my timing cover machined to take the neoprene seal when I had my B18 in bits a few years ago.

[juular]

  On 13/03/2025 at 12:26, warninglight said:

Yes that seal is good news, I expect you have the same type behind the crank pulley too - I had my timing cover machined to take the neoprene seal when I had my B18 in bits a few years ago.

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Good point and worth doing at this stage if not there already.

Between the two scrap engines I had, one had a neoprene timing cover and one had the neoprene rear main housing.  It made sense to yoink them both for the final engine.

[PhilA]

Piston to bore clearance looks about right for that age engine- the expansion coefficient of the iron versus the alloy is quite significant particularly with hypereutectic metals so the rings take that up when cold.

It's also likely the reason people say these engines are indestructible, they don't bind up and score the sealing surfaces when they overheat, there is enough room inside to tolerate it.

Phil

[M'coli]

  On 08/03/2025 at 23:01, Ronkey said:

Also - how do I find out what camshaft I have?

 

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Short of taking it out, a dial gauge on a tappet will give you the lift, and a degree disc/protractor on the crank will let you work out the duration.

[juular]

  On 13/03/2025 at 14:59, M'coli said:

Short of taking it out, a dial gauge on a tappet will give you the lift, and a degree disc/protractor on the crank will let you work out the duration.

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If you do take it out, the revision is stamped on the end of the shaft. It will probably need a clean for you to be able to see it.

I rejoiced at having a 'D' cam below, but later after blowing the engine up I took it out and clearly saw it was a 'B'

[Ronkey]

@Mr Pastry, @juular, @warninglight, @PhilA, @M'coli - thanks for the replies. On it and will report back.