Bearing scraping film

[jansens]

I just came across this old film about bearing scraping: 



I recently had to buy a set of scrapers to relieve the corner of one of the main Babbit bearings in my Riley engine. The new crank has more of a radius on the journal so needed to chamfer the corner of the bearing a little more. That was easy enough but it is interesting that the set of scrapers I bought were just like the ones shown in this film. Is this the standard set for scrapers? A lot of old manuals/articles talk about scraping but I have not actually seen a good description of the process as shown in this film. I was just wondering how good a demonstration this is?

The crank and rods I am using in the Riley engine (Arrows) are more modern design and use shells (so I will run an oil filter) so I don't actually need to scrape anything this time round but it looks like a useful skill to have. I always wonder though in modern engines with shells they always say check the clearances with plastigauge but then never say what the hell you're meant to do if it is wrong! With a new precision machined crank and modern precision shells what are you supposed to do if the clearance isn't right? Send the crank or rods back and complain?

Simon

[Bob Culver]

With such a satisfying time consuming hobby who needs the internet or TV? The difficulty is to avoid chatter marks. Plastigauge is only reliable when newish. It dries hard. it recently dawned that after a myriad tightenings over the decades during refitting sessions the conrod bolts on my car must be near their fatigue limit! Most older books recommended a larger contact area than acheived there, although a thin layer of blue can be very thin.
For car bearings a slight full or near full width clearance increase at the parting line is now general practice.
Scrapers can be made from old files but must not get hot when grinding.
To the 1940s at least on cars without filters it was considered good practice on major overhaul to tighten the caps and relieve with a generous scraping. This removed the hard dirt embedded layer and gave a low wear arte bearing material as new. The surface of old bearings is like a snail shell and hard to scrape. When heavily scraping rods easy to alter the alignment.
it was common to fit to just nil clearance but this now considered dubious practice in car engines..

[Colin Reed]

Hi Simon,
Regarding Fitting Bearing Shells,
The bearing housings Main & Bigend need to be cleaned and the Caps torqued down in place you then need to check for ovality
and diameter if this is wrong they will need to be resized before you can do anything.
If they are OK a light coating of blue on the housings then fit the shells and torque up, release one bolt or stud and check with a feeler gauge between the top and bottom of the housing this will tell you if there is crush on the shells this is required to hold the shell in place.
Then remove the shells and check that the blue is completely covering the back this is because there will be no heat transfer between the shell and the housing on any area that has not blued leading to a run bearing in that case the bearings go back
 I use ACL race Bearings and on them you can mix and match thicknesses to get what you need.

Colin
NZ

[A G Wood]

I recently had to buy a set of scrapers to relieve the corner of one of the main Babbit bearings in my Riley engine. The new crank has more of a radius on the journal so needed to chamfer the corner of the bearing a little more. That was easy enough but it is interesting that the set of scrapers I bought were just like the ones shown in this film. Is this the standard set for scrapers? A lot of old manuals/articles talk about scraping but I have not actually seen a good description of the process as shown in this film. I was just wondering how good a demonstration this is?

The crank and rods I am using in the Riley engine (Arrows) are more modern design and use shells (so I will run an oil filter) so I don't actually need to scrape anything this time round but it looks like a useful skill to have. I always wonder though in modern engines with shells they always say check the clearances with plastigauge but then never say what the hell you're meant to do if it is wrong! With a new precision machined crank and modern precision shells what are you supposed to do if the clearance isn't right? Send the crank or rods back and complain?

Simon
[/quote]

There's at least one career marine engineer and at least one career engine rebuilder on here (not to mention some skilled amateurs) who will  probably evaluate the scraping technique!
I have a boxed set of Moore & Wright scrapers, they're quite small (150 long), there is a triangular, a flat and a curved one in the set, but the curved one is more gradual in the curve compared to the one in the film clip.
I've never used them on bearings, they're mostly been used for chamfering cylinder bores and reducing burrs on surfaces.
The instruction to check modern engine bearing clearances with plastigage [and checking 'nip' and 'crush'] is more a last minute check to make sure one's engine reconditioner of choice  has supplied the correct undersize bearings, and also the o.d. of the shells matches the main bearing and conrod big end bores. Ford, for one, could oversize them which could cause problems for the unwary further down the track.
Your supposition of sending them back and complaining is exactly right, an added expletive-laden tirade would also be in order
Edit: There's one of the engine reconditioners, how do you rate the technique Colin?

[Colin Reed]

HI All ,
The Technique is fine if there is no means of Line Boring  ie out in the wop wops
If you have new cast bearings have them machined ,
I have had to do scraping on 8 inch crusher bearings in Rhodesia took 3 Days
Used Moore & Wright Scrapers

Colin
NZ

[Jacob Fowkes]

   
I’ll drop this one round for you to practice on lol

[Colin Reed]

Hi Jacob,
Leave it in the boot am to Old to pick them up now

Colin
NZ

[Robert Leigh]

I hand scraped a set of 10 thou undersize big ends to fit a new Phoenix crankshaft. I could not find anyone at the time willing to bore the old metal; they all insisted on remetalling. Not wanting to get involved with that much time and money I decided I had nothing to lose. I had scraped larger 6" bearings for machines when I was at GEC Witton, so the technique had to be similar but on a smaller scale. Not having any scrapers I sharpened the back of an old hacksaw blade; holding it slightly curved it works fine. By tightening the bigend so that it would just turn on the dry shaft a couple of turns will mark the white metal on the high spots. A gentle scrape will leave a situation where retightening will show other high spots. When you have repeated the process enough you get to a point where things are right for reassembly. Patience is essential, and four rods took nearly 8 hours, but after more than 20,000 hard driven miles the bearings were still good on dismantling for a different problem.

[Bob Culver]

Colleagues associated with Ford 10s routinely scrape bearings from one size to another close.
It is tedious to set up in a lathe, esp for small removal, and if lathe has no saddle attachment slots.Someone here some time ago reduced by clamping on a hardwwod plug in the chuck, boring half way, then clamping on a larger plug and finishing. Fit finally by scraping. However easy to lose alignmemt.which gives something else to check.
In the film no mention of a reamer for the solid bush. Reamers do not always manage very light cuts well.
I was amused some years ago at a swap meet. A guy with a very strong Pom accent was trying to explain to an enquirer what he was selling. "Baarring scraarper" I dont think the enquirer ever figured it out.
I have read that after run in the progressive build up of embeded dirt in soft white metal bearings often actually reduces the clearance measurably. The crank on my car was only worn about .001 at 100,000 which makes those heavy ugly filters questionable( Unless using Dynanator timing gear!!)

[jansens]

The white metal in the Riley on mine was line bored. They are plain bushes and not with caps. The rear one is in the block and the front in an aluminium cover that goes on after the crank. So no caps to worry about there. The rods are new so I am hoping they are correct! The new crank was slightly larger diameter but there was enough 'meat' in the metal to line bore them out. It is getting harder to find people who can do such things it seems. And that was in Wellington! They do say Welly is going downhill so maybe this is the wop wops now! Kind of glad I am getting out.

Colin, I had never heard of Tinopai so had to look that up. Definitely never been there but as a kid we used to holiday up in Doubtless Bay in the far north so went past (more or less) from Auckland back in the day. I don't think I have ever actually been to Dargaville even.

I am pretty sure the crank and rods and bearings as supplied will be fine but I will check them with (new) plastigauge anyway to be sure. The shells supplied are Ford Zetech apparently.

When the people who know are all gone all we will have left is these sorts of old YouTube films showing how things are done. But they don't show how things are done in the real world I guess so it's very interesting to see the comments here.

Simon