Thread: Budget friendly straightedge

Originally Posted by Widget1983

if I tilt the ruler slight forward/back it can change the size of the gap between the ruler and surface, making the reading not quite accurate.

Save money by sticking with what you have.

When you tilt the thin straightedge and it bows slightly, the edge nearest the deck will drop or rise a fraction. Just measure everything with the straightedge perpendicular to the deck for consistent measurements. Establish this with magnetic 90 degree corners on the deck holding the straightedge, so it's steady unlike holding the straightedge with one hand while using the feeler gauge with the other. Magnetic welding clamps will do, as long as you clean all swarf and other debris off them for a clean fit. Even if they're not perfect right angles, as long as they hold the straightedge at a consistent angle to the deck you'll get sufficiently accurate measurements. If the gaps are still outside tolerance, it's time for a visit to a mechanic with better measuring equipment.

I'm assuming you have metals which will hold to a magnet.

Hi 419, thanks for the feedback

Using a magnet is a good idea. Both the ruler and deck are magnetic, so I'll give that a shot.

Regarding the ruler though. I used a piece of glass tonight to test the ruler, changing orientation, flipping the ruler so each side gets used. It seems I was still getting inconsistent readings even though I held the ruler perpendicular, so I dunno. The description when I purchased it said "precision straight cut edge", though it doesn't specify which edge (if not both) or the tolerances. I've contacted the store I purchased from & asked about the manufacturer as I couldn't find one when searching online. I thought it 'Daytona' was a top American tool brand, but nothing came up, so maybe I was thinking of some other business.

Hopefully I get some info before the weekend so I can find out.

Regarding visiting a mechanic, unfortunately out of the question lol. Block is till in the car with no means of taking it out. I could call a mobile mechanic, but at the cost, I could probably buy a good straightedge lol.

If I wanted to get a 2nd opinion on the straightness of the ruler, what type of place/business would have the means to check the straightness of rulers / straightedges?


Thanks again,

If you have a relationship with your local mechanic you could take your straight edge to their straight edge and check it against each others. It may/may not tell you if yours is straight or not and I’m thinking it will double the error, two wrongs make a bigger gap kind of thing. However it will give you some reference,

cheers

Originally Posted by Widget1983

Regarding the ruler though. I used a piece of glass tonight to test the ruler, changing orientation, flipping the ruler so each side gets used. It seems I was still getting inconsistent readings even though I held the ruler perpendicular, so I dunno. The description when I purchased it said "precision straight cut edge", though it doesn't specify which edge (if not both) or the tolerances.

That assumes that the glass is perfectly flat, which it might not be. If it's float glass, my understanding is that it's pretty flat.

The absence of more information on your ruler might indicate that it's not straight to serious engineering standards. From my limited experience, those straight edges should have something like "accurate to + or - .00X mm / microns".

You can do a reasonable check yourself, which needs to be on one edge only. Get some clean flat MDF or similar and clamp your straight edge tight at both ends. Carefully run a razor (NOT Stanley) knife with a very thin blade along one edge, being sure to hold the knife perpendicular all the time so that it doesn't deviate from the edge. Do it only once, so you have a clean line. Remove the clamps and turn the straight edge end for end so that the edge you cut against is now on the other side of the line. If it's parallel all the way, it's straight, or pretty close to it.

Originally Posted by Widget1983

Regarding visiting a mechanic, unfortunately out of the question lol. Block is till in the car with no means of taking it out. I could call a mobile mechanic, but at the cost, I could probably buy a good straightedge lol.

At what they charge, you could probably buy a small straight edge factory.

Originally Posted by Widget1983

If I wanted to get a 2nd opinion on the straightness of the ruler, what type of place/business would have the means to check the straightness of rulers / straightedges?

Engine / cylinder head reconditioner. Small general engineering workshop.

What makes you think the block could be warped? Normally the head warps if there has been a temperature problem.

what breed of car are you working on? mention the wrong brand and some here may not want to help

Originally Posted by 419

That assumes that the glass is perfectly flat, which it might not be. If it's float glass, my understanding is that it's pretty flat.

The absence of more information on your ruler might indicate that it's not straight to serious engineering standards. From my limited experience, those straight edges should have something like "accurate to + or - .00X mm / microns".

You can do a reasonable check yourself, which needs to be on one edge only. Get some clean flat MDF or similar and clamp your straight edge tight at both ends. Carefully run a razor (NOT Stanley) knife with a very thin blade along one edge, being sure to hold the knife perpendicular all the time so that it doesn't deviate from the edge. Do it only once, so you have a clean line. Remove the clamps and turn the straight edge end for end so that the edge you cut against is now on the other side of the line. If it's parallel all the way, it's straight, or pretty close to it.

Engine / cylinder head reconditioner. Small general engineering workshop.

True, the glass is only 3mm thick so it's possible it could also be out.

Normally when I see something that's considered a 'straight edge' they do have a tolerance reading on it (0.001", 0.0015", 0.002" etc..) but a few (especially rulers) don't seem to have it mentioned, so I thought it might be better to get something that's a straight edge with a tolerance so at least I know it 'should' be straight to a certain thousandths of an inch.

Thanks for the test suggestion, I'll have a look at Bunnings, see what they have. What do you mean though about using a thin razor blade and not a stanley blade? I only have this on -hand;

razor.jpg

Originally Posted by Treecycle

What makes you think the block could be warped? Normally the head warps if there has been a temperature problem.

Not warped, but low spots, particularly the thin section between cylinders, I was getting readings >0.002" sometimes, that's why I considered getting a proper straight edge in case the ruler wasn't straight or only straight to something like 0.003" +/-. I considered using a sheet of glass & sand paper to rub the surface to see high/low spots, but the only sheet of glass is the one I tested earlier (which 'could' be out also).

Originally Posted by Tonyz

what breed of car are you working on? mention the wrong brand and some here may not want to help

Nissan Pulsar lol.

Originally Posted by Widget1983

Thanks for the test suggestion, I'll have a look at Bunnings, see what they have. What do you mean though about using a thin razor blade and not a stanley blade? I only have this on -hand.
razor.jpg

That'll do.

I was thinking of this type. I reckon they have sharper blades than Stanley knives which are built for tougher work.



A super sharp pencil point will do as long as it's not pressed too hard so it keeps a consistent line for the test.

Originally Posted by Widget1983

I considered using a sheet of glass & sand paper to rub the surface to see high/low spots, but the only sheet of glass is the one I tested earlier (which 'could' be out also).

Keeping abrasive particles out of the cylinders is the issue here.

Carbon paper is a safer option, if you can find it. It's in the back of lots of invoice books etc but you end up paying for a couple of hundred pages of invoices you won't use to get one lousy sheet of carbon paper. Don't ask me how I know this. I think there's some way of doing a similar thing with a marker pen on the deck but I can't remember how to do it.

Originally Posted by Widget1983

Not warped, but low spots, particularly the thin section between cylinders, I was getting readings >0.002" sometimes, that's why I considered getting a proper straight edge in case the ruler wasn't straight or only straight to something like 0.003" +/-. I considered using a sheet of glass & sand paper to rub the surface to see high/low spots, but the only sheet of glass is the one I tested earlier (which 'could' be out also).

It's been a very long time since I had to measure a deck for flatness, but from ancient memory about .002" sounds like it could be within tolerance for some engines. Or maybe I'm dreaming. Are you working on the basis that the deck should be absolutely flat, when generally it doesn't have to be, or the tolerance specified for your motor?

Originally Posted by 419

Keeping abrasive particles out of the cylinders is the issue here.

Carbon paper is a safer option, if you can find it. It's in the back of lots of invoice books etc but you end up paying for a couple of hundred pages of invoices you won't use to get one lousy sheet of carbon paper. Don't ask me how I know this. I think there's some way of doing a similar thing with a marker pen on the deck but I can't remember how to do it.

Originally Posted by 419

It's been a very long time since I had to measure a deck for flatness, but from ancient memory about .002" sounds like it could be within tolerance for some engines. Or maybe I'm dreaming. Are you working on the basis that the deck should be absolutely flat, when generally it doesn't have to be, or the tolerance specified for your motor?

That's the downside of sanding the block flat / straight with the engine still installed. I would have to plug any/all holes before doing it though, which it a pain. My understanding is it doesn't have to be totally flat, just straight and any low spots within tolerance (which I'll have to double check). I have the Permaseal brand gasket & I have this PDF from them which talks about head surface before installing gasket (Page two, bottom right)

BeforeYourHeadGoesOnTheBlock.pdf

It mentions
4 cylinder & V8 engines
Length: 0.102mm (0.004”)
0.051mm (0.002”)

permaseal block distortion image.jpg

Q: Which direction are they referring to when they say "length & width". Is the horizontal line (top & bottom) length and diagonal is width?

Fel-Pro, another gasket maker states in a document (last page, bottom-right),

"For example, no block or cylinder head should exceed .003” out-of-flatif there are 3 cylinders, as there would be in an inline-3 or V6 engine.Inline-4 and V8 applications should never exceed .004” out-of-flat andso on. No block or head should be more than .002” out-of-flat acrossthe width of the surface"

Fel-Pro TechTip_How to Prepare an Engine Surface for Gasket Installation.pdf

Regarding carbon paper, you mean this stuff

Raimarket 100 Sheets Black Carbon Transfer Paper with Embossing Stylus Set and Mechanical Pencil for Wood Copy | Premium Quality Carbon Paper : Amazon.com.au: Home

I was considering getting 'bearing blue' or just using a permanent marker (or even carbon paper as you suggested), mark the surface then sand back with either sandpaper or sharpening stone to reveal high / low spots. But it's the low spots I don't know how deep, that's my current predicament. Use the ruler but setup with magnets to make it perpendicular to the surface & see if that helps, or invest in an accurate 18"+ (400-500mm) edge.

I'm a tad confused with the test after reading it again. I drew an illustration of what I think you're saying. Is this right?

ruler check.jpg
Then flip ruler ends & see if the cut in the mdf lines up?

Float glass has a tolerance to cover the so-called flatness I used to work in a facility that used lots of glass, management had words with manufacturer about flatness.

Originally Posted by Widget1983

I'm a tad confused with the test after reading it again. I drew an illustration of what I think you're saying. Is this right?

ruler check.jpg
Then flip ruler ends & see if the cut in the mdf lines up?

Yep.

Just to clarify, the aim is to mark a line along one side of the straight edge and then turn that edge through 180 degrees to check the same edge against the line from the other side of the line. So, on your sketch you'd mark on the side with MDF circled and turn it 180 while keeping the ruler flat on the board so that the ruler is now on the MDF circled side of the line with the same edge against the line.

Originally Posted by Widget1983

It mentions
4 cylinder & V8 engines
Length: 0.102mm (0.004”)
0.051mm (0.002”)

permaseal block distortion image.jpg

Q: Which direction are they referring to when they say "length & width". Is the horizontal line (top & bottom) length and diagonal is width?

Length = the longest section on the block or, on a 4 cylinder Pulsar, the line along cylinders 1 to 4. Width is 90 degrees to length.

Originally Posted by Widget1983

Fel-Pro, another gasket maker states in a document (last page, bottom-right),

"For example, no block or cylinder head should exceed .003” out-of-flatif there are 3 cylinders, as there would be in an inline-3 or V6 engine.Inline-4 and V8 applications should never exceed .004” out-of-flat andso on. No block or head should be more than .002” out-of-flat acrossthe width of the surface"

Both gasket makers state that .004" along length is the out of flat tolerance for a 4 cylinder, so you seem to be within that even if your straight edge is a bit wonky.

If you're using a thin ruler and that's allowing a bow to interfere with accurate measurement, you could try clamping a straight piece of rigid timber or metal to it at a few points to stop the flex, while leaving clear projection of the ruler a few mm below the timber or metal reinforcer.

Originally Posted by Widget1983

Regarding carbon paper, you mean this stuff

Raimarket 100 Sheets Black Carbon Transfer Paper with Embossing Stylus Set and Mechanical Pencil for Wood Copy | Premium Quality Carbon Paper : Amazon.com.au: Home

Yep.

Horses for courses sir. You are trying to use a marking out straightedge to make precision checks for straight and flat. Even the 40mm x 5mm straight edges you linked to early in the piece are really just fancy marking straightedges.

The type of device that you would normally consider for a precision job like you are attempting would be a hand scraped camelback straightedge or possibly a substantial hand scraped I beam straight edge. Both of these would have a precision working surface in the order of 25-30mm wide, so that they are able to sit perpendicular to the surface being checked without being held or flexing due to externally force when being held in position.

The basics of this is that you start with a tested master surface plate, and generate a working surface plate from that. You then ink up the working plate and gently rub the precision face of the straight edge on the working plate, and remove it. Some parts of the precision face will have ink transfer and some won't. The places with ink transfer are high spots and those without are low spots. The high spots are then scraped with a carbide scraper which typically removes less than 0.00005inches per pass from the surface. Once all the transferred ink is removed, the surface is cleaned and given a light stoning with precision ground stones to remove any minor burrs, then taken back to the inked working surface plate to be inked again. This cycle is repeated until you achieve consistent ink transfer to the straight edge. The straightedge can then be used either with feeler gauges or by using ink transfer from the straightedge to the job to test flatness.

Do not consider using abrasive paper etc to cut ink on the surface to identify high and low spots, you will damage the surface and leave it in worse condition because you will not be able to keep the abrasive surface flat enough and contact pressure even enough to avoid getting false indications around the edges of the block and cylinders, and all penetrations for water and oil flow, studs, holts etc.

Basically, if both mating surfaces are prepared on a properly rigid machine, they should be flat enough to seal properly with an appropriate head gasket and properly torqued bolts or nuts. If they are not that flat, no amount of mucking around by a backyarder will solve the problem without creating others, like excessive piston jut out of the cylinder.