Author Topic: Checking bottom end  (Read 645 times)

Online Greybeard

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Checking bottom end
« on: 15.11. 2015 17:39 »
I'm going to strip my Plunger A10 engine soon. I'm going to change the camshaft. The cam I put in there is a reprofiled and rehardened old one; I'm not happy about it.
When I restored the machine a few thousand miles ago I changed the drive-side bearing but left the timing side bush alone as I couldn't feel a lot of slack in the fit of the crankshaft. What is the best way, (for someone without expensive precision tools) to check the bottom end bearings?

Online RichardL

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Re: Checking bottom end
« Reply #1 on: 15.11. 2015 22:00 »
The first ime I had to get a precison measurement on the timing-side bush, I just found the nearest machine shop (not automotive, in this case) and paid them to measure it for me.  Precision within 0.0005" I would guess. They did it by using precision dowells from a reference set, finding two whose combined diameters just fit within the diameter of the bush. The machinist thought this would be more accurate than other tools he had. The small crank journal is easy to measure with a micrometer.

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Offline edboy

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Re: Checking bottom end
« Reply #2 on: 15.11. 2015 22:45 »
the bsa bush and crank journal will wear oval and the journal would then need a regrind. but if you have little wear and just want to boost oil pressure a little renew the bush and ream to suit bush journal. i measure with a 1- 2" micrometer for journal and an internal sprung mic/vernier for bush. another crude way i suggest is to measure the clearance with feeler guages but i ve never tried it myself. sometimes that method is used by  re-borers who ask you to supply a piston to check clearance and measure cut.

Online KiwiGF

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Re: Checking bottom end
« Reply #3 on: 16.11. 2015 02:18 »
To add to edboys post you can assess wear by measuring for ovality of the journals, I think there will be mixed opinions on the amount but, for me, more than 002 inches ovality indicates the need for a re grind, and a good micrometer will easily measure 002, as the bottom end is apart you might as well replace big end shells on the basis it should reduce any clearance due to wear that is present, and they do not cost too much, this is assuming enough miles have passed since the bearings were last done to cause at least some wear.

A machine shop will have the tools to measure crank journals and big end I.d. to much better than 001 accuracy but if you replace the shells there is no need to be doing that sort of measurement, again just my opinion!

A new main bush if fitted should be correctly honed to size, there is plenty of info on that topic on the forum......
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Online RichardL

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Re: Checking bottom end
« Reply #4 on: 16.11. 2015 05:22 »
Well, I thought GB was reffering to timing-side bush, only. Big-end joirnals should be measured with a micrometer and the clearance within the bearing shells measured by Plastigage. http://www.plastigaugeusa.com/how.html

Richard L.
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Online beezermacc

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Re: Checking bottom end
« Reply #5 on: 16.11. 2015 09:09 »
If you haven't done so already I would invest in a good 1" - 2" micrometer. The timing side journal should be measured for ovality. I would not put it back if there is more than 0.001" ovality. Most wear tends to occur at the bottom of the journal as a consequence of combustion pressure on the crank. Also beware of the lip at the outside edge of the journal. If the journal protrudes slightly beyond the bush when it is running it will develop a lip on the outside edge which must be removed, so checking the depth of that lip relative to the rest of the journal will also give an indication of wear. If you decide to have the timing side journal reground you don't have to take it down to the next undersize, an alternative is to remove the ovality by removing a few thou then buy a solid bronze alloy bush which can be reamed to fit the new crank size. If you need any help you know where to find me!
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Online Greybeard

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Re: Checking bottom end
« Reply #6 on: 19.11. 2015 18:40 »
OK, thanks guys. I still don't see a way of measuring the wear in the bush at home. I could buy a two inch micrometer but that only tells me the crank journal size. What about putting a clock on the crankshaft to check slack while the case is still together?

Offline chaterlea25

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Re: Checking bottom end
« Reply #7 on: 19.11. 2015 19:02 »
Hi GB,
Quote
What about putting a clock on the crankshaft to check slack while the case is still together?

Yes that will work, rotate the crank a little at a time and check say every 30 -45 degrees
Of course this still wont tell you which part is worn, its a good basic check though

HTH
John
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Offline v8ivor

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Re: Checking bottom end
« Reply #8 on: 21.11. 2015 17:09 »
Hi GB,
I haven't got into it as deeply as you, but I couldn't feel any play in the bottom end or see any signs of wear, so I'm just about to re-assemble
my 52 A10 plunger motor but I just wanted to check with you that there is no oil seal as such on these mains is there ?

Online Greybeard

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Re: Checking bottom end
« Reply #9 on: 21.11. 2015 23:33 »
Pretty sure there is a seal on the drive side.