Getting ready to have my crank offset ground. What is the maximum allowable side clearance? Crank will be ground to 1.85" journal, 3.6" stroke. I have a set of Carrillo rods with a big end width of .890". Im assuming that if you add the width of two rods together it gives you 1.78". With the crank journal width being 1.81" and subtracting the big end width of the rods that leaves me with .030". Is that too much side clearance? Also, what rod bearings are used with these rods? My research has led me to Clevite CB-1780H STD bearings. Thanks for the Help!

DiLL

I will suggest that you mic the I.D. of the bearing holes in the connecting rods you have.  There are two different Honda rod bearings with each having two slightly different O.D. measurements.  The journal measurements are the same for each though.  For the Eagle and Cunningham connecting rods using the Honda rod bearings, I use the Mahle/Clevite CB1780H, CB1780HX, CB1780H-001, or the ACL 4B1912H, 4B1912HX, 4B1912H-.025.  While the 1780H is the std bearing, the 1780HX has an additional 0.001” clearance while the 1780H-001 has 0.001” less clearance.  The uppers and lowers on these bearing sets can be mixed so that 0.0005” changes in oil clearance can be made. The Oliver parabolic beam rods I have for the Y (6.750” long) use the other part number bearing with a different O.D. and that part number currently eludes me.  The other option is to call Carrillo and get their recommendation for a bearing number.

I will typically target for 0.020”-0.025” rod side clearance for a street engine.  No problem with 0.030” though for a more performance minded engine.  When grinding the crankshafts to a smaller journal so that they can be offset ground, I will aim for no more than a 1.810” journal width on the cast cranks to keep from intersecting the oil supply holes going through the journals at the journal edges or filets.  Steel cranks seem to be more prone to exposing the oil holes at the filets when widening the journals so be cautious about that.  Cutting the crankshafts to the full width to accommodate unmodified 0.940"-0.945" rod widths when using the wider aftermarket rods increases the chance for the oil holes to be exposed at the journal edges and especially when grinding the crankshafts for the Honda rod journal.

With that 1.810” journal width number in mind, the connecting rods are cut so that they are 0.895” wide for 0.020” rod side clearance.  For the Engine Masters competition engines, rod side clearance is targeted for 0.100” or more and then the wrist pin end of the rod is shimmed accordingly so that the rods do not connect each other and/or the journal edges.  In this instance, any metal to metal contact is being minimized.  Keep in mind that the connecting rod side clearance has no effect on the oil pressure so excessive clearance is not a player in that regard.

Lorena, Texas (South of Waco)

Dill  I have a couple of questions about your project as Iam interested in doing a offset grind on 312 crank (2" journal).   What lenght rods, customs pistons ? I guess you are using a 292 crank. Did you find a crank grinder that can leave oil sling and how do check to be sure it is indexed right?  Would like to hear all details. Thanks

Ted, thank you for the information!  I guess I should mention that the bearing holes measured out at 2.008" Which was what lead me to thinking that if the crank was ground to 1.85" that the 1780H STD would work. 

@ COS the rods are Carillo (from eBay) the specs are  Length: 6.350" Journal: 2.008" BE width .890, wrist pin .827", pin end width: .820" and weigh 535g. They  came with new SPS Carr bolts. Yes, the pistons will have to be custom and they will fit a 3.81" bore and will need to be sized for the rods im using. I'm leaving it up to the machinist to spec them out for me as my engine will need a lower compression to support 8-10 psi..  The crank is a C1TE steel crank that measured 2.188" on all the journals. As far as the oil slinger goes I don't think it'll be an issue as it is a 292 size crank. I'm under the impression that the 312 (due to its larger mains) is the only time you have to worry about the stone size because you have to grind the mains to fit a 292 block. I seem to recall reading somewhere on the forum that it isn't the end of the world if the oil slinger gets ground off...Hopefully ted or someone who has more knowledge on this will chime in to confirm. As far as checking the index if you YouTube "checking the index on jakes new crank" Tim McMaster has a video on how to check it. I will however be leaving that up to the machine shop to check. As far as rods for yours go id get ahold of Mummert, they offer rods that will fit a 2" journal. Other than that it'll have ported 113's, Harland Sharp 1.6:1 rockers, EFI and a Mummert DP intake. I spoke with Ted a few weeks ago and he suggested a cam in the 228/238 113 LSA range would work for what im doing so that's probably what ill go with.

DiLL

The lack of the rear oil slinger on the Y crankshafts is not necessarily considered to be a show stopper.  While having that rear oil slinger is desirable, I have not experienced any oil leakage issues as a result of not having it.  This is of course using a neoprene rear seal instead of the original rope type of seal.

The early Ford Y’s did not have those rear oil slingers on the cranks and it was not until 1955 when the rear oil slingers appeared.  Those early blocks did not have the groove in the block to accommodate the oil slinger so if doing a 312 crankshaft in one of those blocks, the slinger would have to be completely removed anyhow.

When grinding the 312 crankshafts to the 292 main journal size, it is preferred to also machine the existing 312 oil slinger so it’s the 292 size.  But in retaining the oil slinger, it does require a narrow grinding rock to do that seal surface.  Because the grinding rock to do that operation is very narrow, it is prone to chatter and breakage.  Hence the reasoning why some shops do not retain the slinger on those 312 crankshafts that are ground to fit the smaller mained 272 and 292 blocks.  On my end, the rear seal area and oil slinger are cut down in lathe and then a narrow grinding stone is used to finish grinding the seal surface.  I typically cut the rear seal surface in the lathe to within 0.010” of where it needs to be and then finish it with the narrow rock on the grinder.  That saves a lot of wear and tear on the grinding rock.  If not using the narrow rock, the oil slinger on the crankshaft would be eliminated without much concern in doing so.

Lorena, Texas (South of Waco)

Ted, do you have any photos of the cranks using the Honda bearings? Curious to see the finished jourals.



Frank/Rebop

Bristol, In ( by Elkhart) 

Is going from a 2.1180 rod journal to 1.85 recommended for anything other than an engine intended for racing? Will the strength of the crankshaft be compromised? I do realize that the smaller journal will have some benefit, regarding reduced friction.

We turned down my 292 crankshaft and indexed it for 3.310 stroke with Honda Rod journal for the 2019 EMC 303Y.  That engine made 461 hp on Ted's dyno when we got back from the EMC competition.  It had about 30 dyno pulls before the competition, and several at the competition, as well as re-testing after we came back.  We had a .600" lift camshaft, tried three different sets of heads, several intake manfiolds, and carburetors.  The dyno testing was done from 3500-7300 rpm on all pulls.  We scored the EMC at 3600-7100 for scoring with 100 rpm run over.  The little 303 Y was rock solid and very repeatable.  I am a bit hesitant to try for more horsepower, however with the cast crankshaft.  We were going to change pistons, up the compression to 11.45:1, and use the Mummert Race intake for the 2020 EMC, but that got cancelled.  I would think a steel crankshaft would be safe at the 500 hp level if it is balanced correctly and assembled for the power intended.  Joe-JDC

JDC

The key to maintaining strength to a crankshaft has to do with maintaining a given amount of material between the main and rod journals.  You can call this the ‘offset’ material.  This explains why FoMoCo increased the main journal size for the 312 engines; when the stroke increased from 3.3” to 3.44”, the amount of offset between the mains and rods would be reduced had the 312 crankshaft stayed with the 2.500” main journal size.  FoMoCo instead went with the 2.625” main journal size for the 312 crankshafts and that restored the amount of offset that was deemed necessary to reduce any potential for crankshaft failures.  For Ford, it came down to keeping warranty issues at acceptable levels for warranty purposes.  If you look at the history of the small block C H E V Y engines in the late Sixties and early Seventies, you’ll see where GM tried to short cut the journal size increases when increasing the stroke on the SBC engines and learned very quickly why there were some minimum requirements for crankshaft offsets. Lots of warranty issues on those small journal 350 engines as broken crankshafts came to the forefront.  Both the mains and rod journal sizes were increased and the issue solved for the 350 engines.  And then when the 400 SBC was introduced, yet another increase in main journal size.  Lessons learned.

With all that being said, when offset grinding a crankshaft for additional stroke, the amount of offset is reduced thus taking some strength away from the crankshaft.  Crankshafts with reduced amounts of offset must be balanced to a much tighter tolerance as any significant degree of imbalance can have an adverse effect on crankshaft integrity or strength.  So yes, any offset grinding of a crankshaft weakens the crankshaft to some degree.

The crankshaft in Joe’s 303” engine was ground for a 0.010” under Honda rod journal (1.879”) but did retain close to the original stroke so any decrease in offset that would have occurred with an increase in stroke was minimized.  The stock Honda journal is 1.889” (not 1.85”) which is ~0.300” less than the stock Y journal size.  On a stock stroke crankshaft, this takes ~0.150” away from the amount of offset material.  As a general rule, I will only go with a 2.000” journal when offset grinding a Y cast or steel crankshaft which minimizes any potential issues with having the offset so small that crankshaft integrity is compromised.  Some of that offset can be retained when offset grinding in the opposite direction for a  stroke decrease as is done for some of the Bonneville engines to decrease the cubic inches in which to meet a specific cubic inch or class requirement.

Do not have a current picture of Y crankshaft ground for the 1.889” Honda journals but there are some Moldex crankshafts here for the Y with the Honda rod journals.  Here's the picture of a 312 rod journal ground to a 2.000” size while also being offset ground to a 3.600” stroke.  With a good balance job, these have presented no breakage issues.

Lorena, Texas (South of Waco)

Thanks for info, taking it all in.