Classic cars forum & vehicle restoration.

[acogman]

Hi all,

The Morris is slowly going back together but we've hit a bit of a problem and I wonder if anyone has any thoughts.
This is probably relevant to most side valve engines....

Okay a diagram first:



So the camshaft (BA32), tappets (BA44) and adjusting bolts (BA45) were sent to Newman Cams to be refaced, everything came back looking superb but the tappets no longer fit in the tappet blocks (BA47). I contacted Newman and they explained the heat treatment process may cause the tappets to swell and suggested reaming out the blocks to fit.

Their original positions in the blocks have now been lost and some slide in reversed but I cannot find a combination where all will fit.
The tappets have a mushroomed end, possibly where they were not moving up and down in the blocks and haven't worn? This doesn't extend far up their length - 1/8", but stops them sliding into the blocks forwards (they need to slide into the block from the top down for the anti-rotation pistons to fit (BA49 & BA50)

I have given them to someone to have a look at but he has concerns as the tappet block bores are tapered, through wear? He can bore them out concentric and remove the mushroomed heads on the tappets but then the fit between the tappets and block will be larger.

I have looked for some guidance but have drawn a blank. I need to get them back before I can measure them but how tight a tolerance are they supposed to run?
If it's too small I assume they would heat up and wear quickly, if it's too large I assume they will chatter and erm.. wear quickly!
Is the best (and most expensive) option to have new oversized tappets made?

Thanks for any suggestions,
Andrew
_________________
Norfolk 'n Good

[colwyn500]

That's an annoying problem Andrew, and one that I think the engineering firm should have been prepared for and should really be prepared to sort out.
I would guess the clearance between the tappet/cam-followers and their guides has quite a range of tolerance but about 0.0010"would be a reasonable starting point
I would leave the guides alone and get a whisper of metal taken off the tappet circumference until the "mushroom" is gone and each just push-fits into a guide. Make sure that each is then kept to its designated bore.

[peter scott]

Hi Andrew,

If I understand correctly I would turn down the tappets so that they are constant diameter all the way. Then determine what needs to be done with the tappet blocks. You may need to sleeve them.

Peter
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http://www.nostalgiatech.co.uk
1939 SS Jaguar 2 1/2 litre saloon

[acogman]

Thank you for the replies and sorry I'm not very good at explaining myself sometimes.

We didn't send the blocks away with the tappets as I expected them only to grind the ends, I didn't know metal swelled that much when heat treated
We probably should have sent them and got the company to fit the tappets back in after wards, oh well.

They did come back looking like new, I even contacted them to make sure they were mine and they hadn't sent back some NOS ones!
It's just a shame they don't fit.

The chap I asked to have a look at them was worried about the finish he would get cutting the hardened tappets on his lathe rather than surface grinding them?
He found the tapered bores in the blocks and was unsure what to do then.

You've pretty much confirmed what we guessed, sort the tappets out them worry about the fit in the blocks.
I hadn't even thought about sleeving them!

I'm going to see him tomorrow to see how bad they are and what we can do.

Thanks,
Andrew
_________________
Norfolk 'n Good

[peter scott]

They probably nitrided (hardened) them. This does cause distortions.

Peter
_________________
http://www.nostalgiatech.co.uk
1939 SS Jaguar 2 1/2 litre saloon

[colwyn500]

Definitely grind them.

[colwyn500]

Definitely grind them.

[PAUL BEAUMONT]

I can't agree more with Colwyn500. It is custom and practice to grind circular parts after heat treatment for just this reason. Heat treatment will cause parts to distort and the distortion is, to some extent is governed by the immediate wall thickness. I am frankly amazed that the engineering firm did not grind them.
They will be impossible to turn I suspect!

Paul

[acogman]

Thank you everyone for the help and suggestions.

I went and saw the chap today, the bores are indeed tapered but not badly, I think he is just too used to modern engine tolerances!
Removing the swollen end and with a very slight ream of the blocks they should fit fine.
He can also grind the tappets so no worries about trying to cut them on the lathe!

Hopefully they shouldn't take too long...

Andrew
_________________
Norfolk 'n Good