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MG MGA - Flat washers- does it really matter?

I'm going to carry a debate from work over to this board. A brand new flat washer has a totally flat side, and a slightly roundish side. The question is: is there a right and wrong way to apply a flat washer, and why?
Mark J Michalak

Mark, in my 50+ years of working on both cars and machinery I've never heard of any 'correct' side out or in for a flat washer. I've never really checked the washers for a flat and curved side, but I'd think this is more of a feature of the stamping process rather than deliberate. I've seen ground flat 'true' washers used for special applications where clearance and torque is critical such as aircraft useage or head bolts. Mostly the washer is there to spread the load and provide a sacrificial surface for a lock washer so that the parent parts won't be marred. Washers used in clamping applications subject to a lot of temperature variation are usually dished and should be applied with the convex side toward the nut to provide a 'spring' effect under expansion and contraction. The washers used on exhaust manifold studs come to mind as an example.
Bill Young

As Bill states, the flat and curved side is a product of metal compression in the stamping process. I have always put the flat side down. More surface contact, and less sharp edges exposed, and it looks better, is the reasoning for my actions. I have never heard or read of any official preference, it's just the way I do it.
Ed Bell

You will note that well made washers are flat on both sides - the OE British ones. It's high production later US stuff that's not flat. I put the flat side against the part. Sometimes there is so much burr on the flat side that I just throw them away. Triumph was the acknowledged leader in sophisticated flat washers - virtually every application had a washer calculated for the job. The Roadster Factory has reproduced many of these - somewhere they have a listing with dimensions for them - it's at least partly in one of the old Spitfire catalogs.

Incorrect flat washers are a very noticeable fault in many "restorations".

FRM
FR Millmore

In days of old, general purpose engineering washers were made to a specific British Standard, defining i/d, o/d and thickness. These days, what is often sold as washers for restoration purposes, bears no resembalance to those old British Standards. Try comparing two washers of the same nominal size, from 2 different sources.
Henry

I have seen quite a few flat washers that were specific to cylinder heads. They were a bit thicker and had the top side edge machined round. This presented a rolled edge look to the finished product,
Sandy
Sandy Sanders

I imagine that there is a right way and a wrong way,just like snap rings or e clips,but for the life of me cannot remember.I think it's sharp edge toward part being held.
gary starr

Round edge towards the nut. Flat side with potentially sharp edge toward the object with the hole in it.
Steve Simmons

I really don't know if there is a "right" way. FWIW...I was once told that the smooth side went against a painted surface to minimize damage to the coating.

Steve
Steve Brandt

So basically, it's asthetics. The difference between the surface area on the round and flat side is miniscule, so I can't imagine it's going to make a difference in most applications. I imagine if there were a slotted bracket application, the flat side would provide greater resistance to sliding.
Mark

NO, the "right" way is for a flat washer to be flat and smooth. Depending on how far off "flat" the trash is, the contact area on the "round" side is approaching a line contact, with "infinite" pressures. The point of a flat washer is to distribute the load over a large area, reducing unit pressure. On the "round" side, the nut or spring washer will still contact over most of the area they cover, so contact pressure there is not much higher than if the washer were correctly made, and any damage is done to the (not) flat washer.

Things like cylinder head washers as mentioned above are specific to the job, and are considered to be "parts" rather than "hardware", and they carry part numbers.

FRM
FR Millmore

If a washer has a sharp edge on one side from the stamping process, it could conceivably cause a stress riser and subsequent cracking in the underlying part, depending on the material it is made of and the amount of stress it is under.
Del Rawlins

This thread was discussed between 02/06/2007 and 04/06/2007

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This thread is from the archive. The Live MG MGA BBS is active now.