Interesting question for one of you technicians

Consulting the Factory service manual, the _main_ bearing caps are numbered for order, and both main and rod bearing caps are numbered 1,

2 or 3 for bearing size, but the instruction for pistons, rods and rod caps are only "keep in the same order" as removed. Unless there is some compelling evidence - such as the reason for the rebuild - immediately after a botched prior attempt, the general advice is to always put the pistons back in the same order. Obviously you know this since you marked them. My guess is you would be creating more problems by changing the order. There is no factory guidance as to cast in numbers on the rod caps, but there are numbers on the main bearing caps shown.

Daniel is right,..those numbers do not indicate which piston goes in which hole,..they are grading numbers (1,2,3) to give the best clearance fit for each rod-bearing (installed) to its respective crank journal. The reason they do this is, is to allow for slight machining differences (diameter) between each crank bigend journal. The difference between the 3 numbers is probably in the area of 0.5 thou/inch or so. You need to install the pistons with their correct rod-bearing caps in the order you removed them.

Jason

I'm aware of the numbering for both the rod and main bearings. Honda also uses a numbering/color mark to indicate the bearing to get the best oil clearance. I've rebuilt a number of Honda engines but not many Toyotas. I don't know if they still use the same system , but older Hondas used a color for the rod bore clearance and a number for the crank clearance. I have run into so many numbers on this engine and I'm wondering what they are all for.

There is a number and a letter on the con rod and cap on one side , this number refers to the bearing size .Don't know what the letter stands for. The other side has a number that crosses the gap between the rod and cap....(half the number on the cap , half on the rod).All the numbers and letters have been stamped with a hand held die. Again , the numbers I'm in question about are cast into place on the bottom of the rod caps. These are numbered 1-4 . The local Toyota dealer couldn't tell me what they mean ???

Incidentally , I had checked for proper oil clearance and that was OK.

Thanks a bunch for your help guys. Much appreciated.

Ken Day

This question should be posted at the Yahoo group. You need to join, but there is no charge. Peopled by a couple of master technicians with many years of experience. Learned some invaluable tips there for replacing the timing belt (remove crank pulley before engine support brace to improve access to bolts), and tips on installing the oil pan sealer around the rear main bearing (go very close to the edge of the pan to avoid leaks). That's the kind of advice you're looking for.

Have you lost the order you pulled the pistons out? If not and the engine had good oil-pressure prior, you dont have a problem.

Compared to older generation engines, modern engines are built to more exacting standards,..but things like keeping the beasring caps mated to its conrod has always been needed.

As modern engines are assembled, each parameter eg bore size and piston grade (another term for piston diameter) are individually matched. The same probably applies to conrod length (as measured between the gudgeon and bearing centre) and piston height ( as measured between the crown and gudgeon centre) to achieve as even a compression ratio for all cylinders. Then we have the issue of individual weight of each piston vs conrod,...and so it goes on... that is what all those codes are for,..to allow the final assembly to be near as perfect as possible. As backyard rebuilders, all we can do is not mix anything up and try to not install and remove things like main bearing caps too often, as they are line-bore checked at the factory and unecessary removal only serves to lose that perfect bore. .There are also other considerations, over time and use, like block distortion, which will cause a loss of line-bore anyway

In other words, there is no such thing as a machine which will, at a reasonable cost, turn-out identical machined parmeters at the end of a run compared to the start,..hence all those codes.

When it comes to bearing shells however, they would all be one size from the bearing manufacturer. Other wise, when it came to buying new sets from your local auto-shop, thered be too many fractional sizes. eg std, std + 1 thou and so on. Instead they usually just have the std oversizes of 10 thou increments.

There's an old saying: there's nothing quite as quiet as a new engine",.....(unless you are prepared to blue-print the old one.)

Jason

No. I marked the pistons before I pulled them out. Maybe I didn't clearly explain what I was wondering about , the numbers that are cast into the bottom of the rod caps. Since they are numbered in reverse order and IF these numbers do represent which cylinder they belong in , then someone has had the engine down before and put it back together in reverse order. But , these type numbers are always ( at least on engines I have torn down) been stamped by hand. I'm really curious as to what these numbers mean. The engine is going back the same way it was when I tore it down. I'm just curious .

I agree.

But the bearings are not all one size. Thats the reason for the codes. There is approx .006 mm or .00025 inch difference in thickness from one size (number) to the next to assure best possible fit . Both rod and main bearings are numbered. You can , however , buy aftermarket bearings that are all one size. They more or less strike a happy medium , but you will in most all cases have varying oil clearances , though usually within acceptable limits.

Thanks for your input. I appreciate it.

Ken Day

I meant the crank-journals are not all the same size hence the selection of conrod with the knowledge of how much the installed bearing shell will yield in terms of rodbearing size.

If they have a crank-journal which is std + 0.5 thou", it is by far the cheapest solution to select a piston-rod assemble which will provide the calculated clearance for that journal. The variation-parameter in the rods which provide this range of selection, would be the rod's bearing circle,..which in this example, would be - 0.5thou". The shells would be a constant in that they are all the same and these *required* slight differences in size would be accomodated by their crush.

In other words: if you have 2 rods, one is std +0.5 thou, the other std -

0.5 thou,..you can still maintain that difference (for fitting to an individual c/shafts which needs them) even tho you are using the same size sets of bearing shells. The thing which will be different tho, is the bearing crush, but not so different to create a problem for the *installed* bearing.

That is my knowledge on the subject which I haven't really read anywhere,..it's an amalgamation of mechanic talk mostly....can anyone confirm or deny this?

Do you mean the bearing shells are numbered so, or the caps?

Only if your rod has gone oval, which can happen in severe service, and or over-rev situations.

Jason

FIRST. NEVER in technical discussion use such lame shorthand as "0.5thou." The correct expression is 0.005" . Now, for the two journals you listed above, you could use the same bearing shell for your journal IF the journals were five TEN thousandths difference (0.0005"). Bearing shells typically come in STD, 0.002", 0.003, 0.005, 0.010, 0.020, and 0.030" undersize. Remember, as a journal wears or is turned-down, it gets smaller. Typical oil clearance on a journal can be 0.00075 to 0.00175".

What did I miss? ;-)

"0.005" is 5 thousandths of an inch. I was using my 'lame' notation to indicate 0.0005" (1/2 of one thou" or 0.5 thou)

I assume you meant to write 0.0005"?

Now, for the two journals you listed

I was asking, is it the case that hand-selected conrods which had bearing-circles (correct name here plse Phil?) matched to the differing crank-journals could use the same shells with the result the correct oil-clearance ( eg 0.00075") was maintained for those two journals?

Bearing shells typically

Is that the case from a retailer? I thought the std range was in 0.010" increments.

OK,..tho that upper limit seems large for a modern engine.

Jason

I wrote precisely what I meant in both instances. See ... this is the confusion *you* created by being sloppy.

Connecting rod "big end" is sized to a standard dimention in the rebuild industry. Now in the OEM manufacturing arena, the "zero waste" policy may well have connecting rods sized +/- one or two thousandths because the OEM has access to bearing shells with one or two larger backing thicknesses yet have the standard dimention to fit the standard journal. This is why ith some manufacturers you will see A, B, C, D connecting rods that were OEM fitted with those shells which denotes backing thickness. Now once you resize the large end of a connecting rod, all those alphabet sizing become invalid.

Depends on the bearing manufacturer, not the retailer.

Depends on the engine block material and intended use. If you bought a BMW M3 which is a racing engine, all the clearances are larger and the oil viscosity heavier for the anticipated use. Also, if the engine is a diesel, crankshaft oil clearances are often in the range of 0.0014" - 0.0037" with an absolute upper limit of 0.0059" for essentially the same sized journal. On the other end, if the engine is a light duty fuel efficient engine (IE, Tercel) then 0.0008-0.002 is normal.

Well,...OK then Phil ;-). For the record, the term 'half a thou' or 3/4 thou is not language exclusively used by me. It is common among reconditioners and mechanics I've spoken to over time.

Yeah, but does rod resizing give us +- zero tolerance? Aren't we faced with the same problem where after resizing a dial-gauge has to be used to give us the real figure, thus if we are chasing perfection we are back in the mix and match thing again?

Now in the OEM manufacturing arena, the "zero waste" policy may

So resizing is an exact science? Fair enough then.

Interesting. I haven't worked on a diesel. Why the larger tolerance? Because ignition occurs later in the cycle compared to petrol,..or because they run larger journals?

I had a Golf petrol engine with 0.004" clearance at the rod-bearings (plastigauged with new shells) which while on the upper limit, was supposed to be an acceptable. Trouble was it had bearing noise once the engine was up to temp and despite having good oil-pressure.

After working on a number of petrol-engines, I've found that to achieve a quiet engine, bottom-end wise, clearances, the upper limit has to be less than or equal to 0.0025". The old rule of thumb: max clearance equals

0.001" per inch of journal diameter" seems close to the money.

Jason

ONLY you and I are in conversation so .... what the heck other people do does not support your case. B^)

Yes, and there is always a tight machining tolerance for resizing rods in the rebuild industry. Additionally, rods *should* be rebalanced on both ends after resizing. The factory is more volume production with "zero waste" than the rebuild industry.

Sizing and resizing needs to be quite precise for several reasons. (1) bearing shells with 2-4 optional backing thicknesses are rarely available to the aftermarket rebuilder. (2) bearing shell crush must be "right." Afterall, it is the 'crush' that locks the shell in place ... not those little tabs at the end of the shell. (3) the finish and angle of the mating surfaces (rod to cap) must be square 'right' so as to minimize cap shift against the rod (this is not an issue with "cracked" rods).

(1)Oil clearances are determined by anticipated oil clearances at operating temperatures. (2)Diesels have about double the cranking compression of gasoline engines. As far as where injection starts with a diesel, this is not so. I have an SD22 Nissan diesel in a little OLD pickup ... base timing is 18 degrees BTDC. Many diesels have much less base timing, say down around 5-7 degrees BTDC. At max load, timing is often in the 28-32 degrees with many diesels. There is an OLD rule of thumb about oil clearances and journal diameter: "0.001" oil clearance per inch of journal diameter." Of course, if you are intent on running very light lubricants, then you'll find about 0.005" per inch of journal diameter. There's a bit o' machinist history for ya.

Agreed. LOL With that Golf engine at 0.004", I would have been running

15w-40 or 20w-50 oils.

I know what the manual says , but do you think .002 clearance on each of the main bearings on a Toyota 2.2 is ok ?

Back in the late 50's when I first started building engines I had no precision instruments to measure oil clearances. Not sure when PlastiGauge came on the market but I didn't discover it until sometime in the 60's. My Dad was a mechanic and he used a lot of 'high tech'measuring devices such as a piece from a Prince Albert tobacco can , an old worn dime , a nickle , Bugler tobacco rolling paper and the list goes on. He used these in an emergency for valves , points , bearings etc. and of course passed this info to me. :-)

Back then , I used a piece of newspaper to check the clearance on my rod and main bearings. If the crank would turn without a paper shim and then lock up with a paper shim inserted , then it was OK. That meant we were somewhere less than .003. I don't what the newspaper thickness is now but it was .003 back then. Boy , was I tickled when I discovered Plastigauge.

I recall when I was just a boy , my Dad pouring babbitt bearings in some of those old cars. The most memorable improvisation was him cutting a leather rod bearing for an old Model to get the guy home. I suppose it worked. I also remememer him showing me how to set up a ring and pinion using a laundry product called Little Boy Blue blueing. I recall him helping me set up 4:56 and 5:13 gears this way and they were as quite those set up with a dial indicator. Are you by any chance old enough to remember blueing ? Things have changed a lot since then.

Thanks

Ken Day

Yes Sir !

In which sense do you mean rebalanced? Or do you mean each rod is balanced wrt eachother?

I have heard that one way to balance a twin cyl, is to strap the 2 rods together with each rod reversed to the other (little-end centre axially aligned with the bigend of the other),..then they are mounted on a knife-edge at the centre of their length. If they are balanced they shouldn't tip.

Is this what you meant?

That particular saying seems to be very widespread :)

To make it worse, the recon shop I took the crank too for a 'second opinion' (my w/shop manual was the first) said it was just within tol and to improve bearing life it should be linished (lol!!) Make the already lousey clearance even wider.

Jason

snip

"Balance: 1)A weighing device. 2)A weight. You support one end of the rod and weigh the other end. Remove metal as necessary to make all rods weigh within half a gram of each other when weighed this way (motorcycles would be closely matched while a commercial diesel might be 4 grams or less. If a lot of metal removal is necessary, then get another connecting rod.

Philip. For what it's worth , I knew exactly what you meant when you said .5 thou and so on. I find that in everyday conversation with the average Joe many don't really understand when you start saying things like " five then thousanths or twenty five ten thousanths", but when you say "1/2 a thousanth or .1/4 thou" then they know what you're talking about. When writing it I use the 'proper' term , but otherwise I just use what fits the company I'm with.

Ken Day