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Short Motor Rebore / Build - Measuring Tools


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#1 JonnyAlpha

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Posted 08 August 2019 - 06:35 PM

Hi,

 

I am having a 1275 A+ Metro block rebored to 1293 and I am looking for advice on measuring tools, for the build. 

Although I trust the machinist I want to be able to confirm the measurements. I also need to measure Piston Deck Height, End Float etc.

 

Like I said it will be bored to 1293 (1275 +20 Thou).

We are using P21253 +20 Pistons aiming for 2.5 to 3 Thou clearance on the bores. 

 

To measure the bores I think I need a set of telescopic gauges would these do the job

 

Also I have read that I will need Plastigauges to check the piston clearance? Again any links?

 

I also need a Piston Ring Compressor - any recommendations? 

 

I have a DTI Gauge and Magnetic stand so the End Float and Piston Deck Height won't be an issue.

 

Any other tools? 



#2 imack

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Posted 08 August 2019 - 06:47 PM

I've got a set of those gauges, they're not that great, you then need the appropriate size micrometer to measure the bore gauge.

#3 whistler

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Posted 08 August 2019 - 06:54 PM

Your machinist will have bore measuring instruments. Mine will measure the bores in front of you and show the results.



#4 Moke Spider

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Posted 08 August 2019 - 08:45 PM

You can get some very good results with quality snap (or telepscoping) gauges, but regardless of quality, don't expect to take any of them from the packet and be able to get perfect results, they take some practice to use. Starett and Mitutoyo are about the only brands to trust for these.

 

In fact, that goes for just about any of this precision measuring gear, they all take some practice to use and get accurate, repeatable results.

 

Plastgauge is for measuring bearing clearances.

 

You can check piston to bore clearances (to a point) with feeler gauges, but again, this takes some practice as it's easy to distort (not permanently) piston skirts and get a false reading. This however, is only a go / no go check though and realistically, is likely OK for for your assembly checks.



#5 mini-mad-mark

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Posted 08 August 2019 - 08:47 PM

MokeSpider beeat me to it about the practice required :

 

I think Plastigauge is used to measure crank bearing clearances not pistons? Pistons are simple bore vs OD measurements, with the right kit of course.

 

Cranks and bearings are a bit more complex as you have the crank, the bearing and then the con rod big end or main cap size so the plastigauge tells you what clearance you have altogether I think. I never used it as I relied on the machine shop to know what they were doing - hopefully...!

 

As mentioned by imack above the telescopic bore gauges are not a direct measuring tool; you use them to match up to the bore size and then you need a micrometer to measure the telescopic gauge to get the actual size, so you need the gauge(s) AND mic(s) to suit - not cheap for the average DIY-er but I am lucky that I could borrow the kit from work if necessary.

 

However I would caution that without a bit of practice most measuring kit is not that easy to use/get the correct size (I worked in Metrology for 7 years) - I have seen people, who should have known better, virtually screw the anvils of a micrometer into the piece they were measuring. 

 

"Feel" is a bit of a thing when it comes to measuring...... most mics have a ratchet clutch to try to keep the torque constant during measurement to give a consistent reading but still needs a bit of "feel" 

 

 

 

Regards



#6 ACDodd

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Posted 08 August 2019 - 11:55 PM

Happy to measure up anything for you verify the machining done by a third party. Saves you having to buy equipment.

Ac

Edited by ACDodd, 08 August 2019 - 11:56 PM.


#7 JonnyAlpha

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Posted 09 August 2019 - 08:48 AM

Happy to measure up anything for you verify the machining done by a third party. Saves you having to buy equipment.

Ac

 

Are you in Salisbury? Not a million miles away but need a good reason to go there. Apart from Mini work of course.

Just wish there were more people available in the deep SW Devon / Cornwall :-)



#8 Retroman

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Posted 09 August 2019 - 10:23 AM

I would suggest trusting the machine shop / engineer

 

They deal with fractions day in day out, with tools they can use correctly and trust.

 

He might show you

 

As Spider says above he only trusts good tools, you as rooky would need to buy a some good tools. The ones you buy may read a fraction different to the machine shop too...and as above accuracy is a 'feel' thing ...this is why they are called feeler gauges...the same thickness can feel sloppy or tight....just touching the sides or too tight...relatively huge differences

 

Going to AC Dodd to have things checked would be fuel well spent (instead of buying tools you will rarely use)

 

He is sure to check it correctly and tell you how good the machine work is (or not !!)

 

You then have peace of mind that your unit is good and can trust the machine shop

 

Make use of the engineers, good ones are becoming an endanger species



#9 DeadSquare

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Posted 09 August 2019 - 10:51 AM

Hi,

 

I am having a 1275 A+ Metro block rebored to 1293 and I am looking for advice on measuring tools, for the build. 

Although I trust the machinist I want to be able to confirm the measurements. I also need to measure Piston Deck Height, End Float etc.

 

Like I said it will be bored to 1293 (1275 +20 Thou).

We are using P21253 +20 Pistons aiming for 2.5 to 3 Thou clearance on the bores. 

 

To measure the bores I think I need a set of telescopic gauges would these do the job

 

Also I have read that I will need Plastigauges to check the piston clearance? Again any links?

 

I also need a Piston Ring Compressor - any recommendations? 

 

I have a DTI Gauge and Magnetic stand so the End Float and Piston Deck Height won't be an issue.

 

Any other tools? 

 

 

When you have measured the "piston deck height", what are you going to do about it ?

 

You say that you trust the machinist, but obviously have doubts. 

 

Mr. Dodds has kindly offered to check the work, when it is done.  If you are prepared to accept him verifying someone else's work, may I suggest that you ask him if he would be prepared do the whole job.



#10 JonnyAlpha

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Posted 09 August 2019 - 12:58 PM

Sadly I suffer from a syndrome (not medical just my personal state of mind), that means whenever I do anything I need to know exactly what and how it is done. If I could do all of the work myself I would but sadly (a) I didn't train as an engineer and (b) I don't have all of the tooling for such a specialised task. Although some would say checking things yourself, even if done by a reputable source, is never a bad thing, we are all human and all prone to the occasional error.

 

To save on costs of shipping / transport, I am trying to get all of the work done locally. Although, Initially, I was considering getting most of the work done by a Mini expert such as Kieth Calver or the likes however the added costs of labour in doing the dry build were playing on my mind. 

 

The machine shop in question has done many A Series Engines and I have no doubt they will carry out the work correctly I just want the peace of mind of knowing exactly what, why and how (as said above).

 

I have asked Mr Dodds for a quote on a couple of other specialised tasks so I may well indeed be taking a trip to Salisbury, but nothing is set in stone as yet. 



#11 JonnyAlpha

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Posted 09 August 2019 - 01:23 PM

 

Hi,

 

I am having a 1275 A+ Metro block rebored to 1293 and I am looking for advice on measuring tools, for the build. 

Although I trust the machinist I want to be able to confirm the measurements. I also need to measure Piston Deck Height, End Float etc.

 

Like I said it will be bored to 1293 (1275 +20 Thou).

We are using P21253 +20 Pistons aiming for 2.5 to 3 Thou clearance on the bores. 

 

To measure the bores I think I need a set of telescopic gauges would these do the job

 

Also I have read that I will need Plastigauges to check the piston clearance? Again any links?

 

I also need a Piston Ring Compressor - any recommendations? 

 

I have a DTI Gauge and Magnetic stand so the End Float and Piston Deck Height won't be an issue.

 

Any other tools? 

 

 

When you have measured the "piston deck height", what are you going to do about it ?

 

 

 

As I understand it, (and I'm sure you do too), once the rebore and hone have been done we build up the Crank and Pistons and then measure the Piston to Deck height at TDC, (rising pistons). This will tell us how far down the bores the piston crown is and ergo how much to skim off of the head to get the desired PDH.

From my research, 10 thou (0.010")  seems to have been recommended for this type of build. 



#12 JonnyAlpha

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Posted 11 September 2019 - 06:33 PM

Ok going back to the tooling question, IF I were to decide to invest in a set of measuring tools I need a steer with regards to what I would need to buy.  

With regards to manufacturers Mitutoyo and Starett have been mentioned but where do Moore and Wright fit in as far as precision tools go?

 

With regards to Micrometers, for the pistons I'd need a set of 2 - 3" Micrometers and have looked at the following:

 

Micrometer: Mitutoyo

Micrometer: Starett

 

Both of these have a 0.001" graduation, is that precise enough?

 

And for bore gauges:

 

50 - 160mm https://www.machine-...bore-gauge.html

 

What else?



#13 DeadSquare

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Posted 11 September 2019 - 08:02 PM

There is a brand new Chronos 2"-3" on ebay for £14-95, but a Chinese vernier from Aldi is just as good and easier to use for what you want it for.



#14 alex-95

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Posted 11 September 2019 - 08:23 PM

There is a brand new Chronos 2"-3" on ebay for £14-95, but a Chinese vernier from Aldi is just as good and easier to use for what you want it for.

Is this a Joke?



#15 DeadSquare

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Posted 11 September 2019 - 11:00 PM

Of course it isn't a joke.

 

I write as a precision engineer. 

 

1)  For someone who is unaccustomed to precision measuring, all imperial micrometers have .001" graduations.

 

2)  The jaws of a digital vernier ( which reads to half a thou ) are far easier and in this case, more accurate to use than a micrometer;  but should the micrometer be the instrument of choice, a brand new Chronos, complete with its 2" gauge, will read as accurately as an inexperienced user can use it.

 

80 or 100 years ago, Chesterman probably made the best widely available measuring devices in the world, by hand.  Today, computer controlled machines make them more accurately.

 

Both Moore and Wright, and Sterett have long standing reputations, but whereas most Moore and Wright micrometers incorporate a .0001" vernier,Sterett often don't.






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