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+--- Thread: Scraping white metal bearings (/showthread.php?tid=4950)
RE: Scraping white metal bearings - Colin Reed - 15-09-2020
HI COLIN,
What is wrong with the pistons that they need to be replaced after less than 1000 miles from rebuild,
from my point of View it would seem to suggest the rebuild regarding pistons and big ends was poorly done,
also it would be much more easily done with the crank on the bench as you will be hoping to get more than 1000 miles and not waste money on pistons if you do not sort the big ends out properly.
i am not being negative but do not rush the job take a bit more time and get it right.
Colin Reed
NZ
RE: Scraping white metal bearings - Colin Wilks - 15-09-2020
Hi Colin
The pistons were an unmatched set condemned by a good friend whose engineering advice I trust. It's easy to blame the bloke who was there before, but I am fairly sure the engine builder was presented with a selection of used parts and asked to sort it as best he could within a limited budget. The previous owner who commissioned the rebuild used the car very little and so probably had no aspiration to get 60,000 miles out of the rebuilt engine.
As an enthusiastic amateur enjoying picking up the spanners after a hiatus of several decades, a frustration I have with these old engines is to understand what, whilst less than ideal will nonetheless "do the job". For now I want to get what I 've got operational, and I think what I'm doing should deliver four reasonably well fitted and balanced rods. They're not going to be perfect, it's the first time I've scraped in a bearing, so it will be interesting to see if they last.
RE: Scraping white metal bearings - Stuart Giles - 15-09-2020
(15-09-2020, 01:22 AM)Bob Culver Wrote: Plastigauge is intended for modern bearings with a definite clearance. Likely to damage a bearing with no clearance.I'm a bit surprised by this statement as the documentation I have from Hoyt recommends the same clearance per inch diameter of the crankpin using their babbitt style metal as Mahle etc. do for their modern shell bearings. This ends up as being about 1 and half thou' on an A7 motor, When I've bored metalled big ends for splash fed motors I aim for at least a couple of thou clearance on the basis that more oil flow equals more cooling and less chance of a "run" bearing. Anyone who has stripped a motor with "a bit of a big end knock" will know that the clearance on the dud rod to the crankpin will be measurable in fractions of an inch rather than a few thousanths.
RE: Scraping white metal bearings - Robert Leigh - 15-09-2020
When I first built a half decent engine for my Ulsteroid I bought a new Phoenix crank and looked in my spares for a set of nicely matched rods. The only set worth using had been used with a -10 thou crank. I scraped out the 10 thou by hand taking about 2 hours for each rod (one each evening as I was still working). I used to tighten the big end to a point where it was stiff to turn and then push it round the big end a couple of times. Examining the white metal by eye revealed the high spots which I scraped with the sharpened back of an old hacksaw blade. The engiine ran very well for more than 20,000 miles, at which point Fenella said it was getting noisy. The problem proved to be a broken little end bolt. The head had come off, leading to a crack down the con rod. I could not find any more serviceable rods to repeat my earlier exercise, so I had a set re-metalled, and all seems to be well again.
RE: Scraping white metal bearings - Ivor Hawkins - 15-09-2020
I remember having a similar problem on one of my old Ruby motors, when I was a poor skint teenager and packed the rods with pieces of shim...I’m sorry to admit it, but it ran for another five years without a problem.
I suppose whoever has the car now will strip the motor, if they haven’t already and say what sort of booger’s did this? A skint one who drove the 30 quid banger to work every day!
RE: Scraping white metal bearings - Renaud - 15-09-2020
Ha ha! lovely Ivor!
RE: Scraping white metal bearings - Nick Salmon - 15-09-2020
Well done Ivor. I follow your principles to this day...!
RE: Scraping white metal bearings - Zetomagneto - 15-09-2020
Hi Colin Wilks sounds like a bad rebuild, odd pistons, ovality on a reground crank less than 001”
on a reground crank is unacceptable it should be round. Tight bearings, I would be inclined to take the crank and rods to a machinist who can measure the crank, then bore the big ends, at least they will then be parallel and round. If the crank has ovality less than a though getting it ground so that it is round
might give you sufficient clearance. You need someone who can accurately measure the crank, and big ends, and then decide on the best course of action. Plastigauge is good for checking clearance but only does so at one point, it won’t tell you of ovality in either component.
As things stand I fear you are headed for another short lived engine, you don’t want that particulary
with 2 cars sans engines.
Ignore the bodger dodges, do it once, do it properly.
Best Wishes
RE: Scraping white metal bearings - Bob Culver - 16-09-2020
Many homely remedies done in a craftsman manner are entirely satisfactory and will outlive the crank. Bearing loads and rubbing speeds are nothing like moderns. The worn ovality tolerance is more than .001. Any slight ridging can be removed with a fine oil stone and very fine emery paper. Austin cranks are hardly worth grinding and it ruins the vital nitriding on Phoenix. Recondioners are/ were very adept at ruining radii, burning the nitride etc. It has long been recognised that a distinct clearance is the ideal, esp for pressure feed, although in a small dia white metal bearing it can be very small. “Modern” bearings fitted this way often appear as if contact never occurs. When cars ran on dirt roads with splash lube and no air filters wear was significant so desirable to start with minimal clearance. It is very difficult for a reconditoner, even one specialiasing in vintage ware, to bore big ends for exactly .0005-.001 clearance and a perfect finish, esp when each big end may differ, or may be worn. Hence the hand scraping. The high spots soon reduced giving a small clearance . I am sure i have read the fall by own weight guideline in some older textbook. It seems fine at original Seven speeds , and certainly with a slightly oval crank. It is difficult to maintain a good scraped contact if scraping progresses beyond contact. A sharp whack on the cap dry served to give a final freedom. My father used to replace main bearings at regular intervals and refitted rods this way and I carried on. ( In my use, with protracted running at 4000 rpm have noted slight ridging on crankpins, but was running without the top exit holes)
Many caps have been hideously filed. Correction by rubbing on thin fine emery on a piece of plate glass or on a wide fine file plus shims is entirely satisfactory. Many makes were fitted with removable shims. If the outer edge is contoured to match the rod can be located without risk of rubbing on the crankpin, no risk of pieces breaking off, and does not offend the eye!
I have refitted rods from one close size to another and Ford 10 Club members do the same. The difficulty is maintaining the rod square, although with a lathe simple jigs can be made.
As previous when overhauling older cars without filters, it was considered good practice to lightly scrape the bearings. This removed the layer of embedded dirt and reduced the wear rate back to zero. My car was .001 oval at 100,000, sure to outlast the crank, not justifying a filter!
RE: Scraping white metal bearings - Charles P - 16-09-2020
(15-09-2020, 11:06 PM)Zetomagneto Wrote: Hi Colin Wilks sounds like a bad rebuild, odd pistons, ovality on a reground crank less than 001”
on a reground crank is unacceptable it should be round. Tight bearings, I would be inclined to take the crank and rods to a machinist who can measure the crank, then bore the big ends, at least they will then be parallel and round. If the crank has ovality less than a though getting it ground so that it is round
might give you sufficient clearance. You need someone who can accurately measure the crank, and big ends, and then decide on the best course of action. Plastigauge is good for checking clearance but only does so at one point, it won’t tell you of ovality in either component.
As things stand I fear you are headed for another short lived engine, you don’t want that particulary
with 2 cars sans engines
Ignore the bodger dodges, do it once, do it properly.
Best Wishes
Very sensible words.
C