Has anyone got any expeirence with using a dial indicator to measure piston to deck clearance?

I just cant seem to get a consistant reading with the thing.
Plus the bloody piston rocks thus changing my clearance by about 6 thou.

should I just measure it, then rock the piston take that figure add it to the intial one then and halve it?

I am sure its just a case of stupid fingers versus a very delicate guage. Its ok if you want to give me advice I will take it, (I am ok like that )

thanks and a happy W/E to all

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Stick it in the centre of the piston?

I'm worried you can Rock the Piston (why did the word Casbah just strike me)

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Stop Licking the Dog...I Don't Care Who Started It

thats where i was going next,

I will just have to add the piston dish depth to that figure shouldnt be to hard I spose. Will have to wait until I pull the pistons out coz the rocking will still stoodge me, but thats no biggy..

Thanks mate

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This is correct.
Doesn't have to be the absolute middle, anywhere along the centreline of motor will do.

Gafmo, they rock due to piston clearance, even new ones can rock a thou or more.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

my dial has a little knob on it that moves the dial guage about 5mm. Am i supposed to use that to get it from the block over to the piston or do I have to unlatch the magnet and spin the whole thing around? this is the only way I can see it makeing it to the middle of the piston..... fiddley little sucka

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should I keep the base in the same spot and just extend the arms out or should I reposition the base for every test?

I am just having a little trouble getting any consistency is all. I probly should go sleep for a bit and try again in the am.

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Set the arms to whatever length you need to position the dial gauge, which should be vertical.
Then just release the magnetic base to reposition it.
Note the dial face on the gauge rotates, you can zero with that each time.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

OK its a new day I am full of coffee and toast ...having more luck.

What would be the greatest difference I should expect?

I am assuming that due to BMC lack of rulers and such that its the crank throws that are different, or would it be worth juggling the pistons around to see if it helps?....

Until a few days ago i didnt know the conrods were offset so I know juggling them is
not an option.

I am setting the pistons 5 thou out of the block so I want them to be fairly even so I dont smash my valves to bits.

I can get my engine guy to shave the pistons a bit if need be, but then that would affect the amount of piston dish on a particular cylinder thus affecting my CR.

Shouldnt have filled up on toast and coffee, I might want to drink some paint after.

Oh thanks guys

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oh k

After alot of fiddling I have all these numbers to confuse the situation.

firstly, the block to the centre of the piston dish measured as follows

1 = 207.5 tho 2 = 202 tho 3 = 203.5 tho 4 = 203 tho

this would lead you to beleive the stroke is shoter on no 1, not so

these are the figures from the top of the block to the outer edge of the piston (the bit thats going to smash everything if its wrong)

1 = 54 thou 2 = 54 thou 3 = 55 thou 4 = 56 thou.

this measurement was taken inline with the crank. Although the dial would move 3 thou if i rocked the piston so all these numbers may = nothing

Actually now I think of it I might move the piston from no.1 to no.2. Mr V says 2 should be a little lower in CR than its friends.

So its clear the piston dishes are all different and the strokes are all different and maybe the blocks been decked in a manner unparallel to the crank...

I may have to lock the crank some how see if this improves consistancy

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What it tells me is the dish in number 1 is deeper than the others - is it the same batch as the others or was it replaced at some time?

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David L


My greatest fear in life is that when I die my wife will sell my Mini and tools for the price I told her I paid for them!

hi wombat

its a brand new batch of hypertecs, with fiddy thou chopped of em to reduce the dish so I can get a good CR....

I think I will leave the dish out of it for now and just concentrate on getting the highest positions accurate. The dish can be measured when the motors in bits again so the blooding thing doesnt move.

I reakon my next bet is
1) put all the rings on the piston to reduce the rocking

2) mark each piston in 4 equal positions, measure add then devide by 4.

3) all of the above.

the actual figures for the highest point in the pistons are not that far out. I should focus on that....

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