I am starting a speedster project, and I will no doubt use a SCAT Stroker crankshaft. The deal is that they come in two varieties:
1) With 1.590" main bearings.
2) With 1.625" main bearings.
We used to just put Model A cranks in with 1.625" mains, but they were often worn and needed to be turned own a bit which amounted to about the same thing as the 1.590" SCAT. Lang's does not even carry the 1.625" Scat because of main bearing babbit "issues".
My question is: Which SCAT is to be preferred, the 1.590" or the 1.625" and why?
I hope this non-answer doesn't put you off, but I've always questioned the need for a longer than 4" stroke when a T just needs a beefier crank. Do you really need more low end torque? What gear ratios and tire size will it have?
I would never drive one, but I have heard Toyotas have extra long rods for more efficiency. The ratio of rod length to stroke is an important factor, and the T is maybe at the practical limit, as the A rod is longer, with its longer stroke. you can calculate the angle at mid-stroke and compare.
The T rod is 7" long, while the same stroke Chevy rod is 7 7/16" long.
I use a Chevy crank. It is 25 lb, vs. 15-16 lb for a T crank.
A T averaged 85 mph in the 1923 Indy, on 121 cubic inches.
"do you really need more low end torque?"
Is there such thing as "enough" torque?
(hint: the answer is "no")
Ok, Ok, but I still want to know about the main bearing size. Is there a problem with the 1.625" main bearing?
Some seem to think that the babbit is too thin when you go out that big.
Does anyone have any experience one way or the other?
I was told the limit was the distance between the bolts.
Here is what happened, and why I ask the question. I ordered a SCAT Stroker crank from Texas T Parts, and it arrived yesterday. I did not specify the main bearing size when I ordered the crank thinking that what they would deliver was the 1.590" main size. Lang's for example does not even carry the 1.625" main bearing version because of the size issue.
What came from Texas T was the 1.625" version. So I am thinking that I should send it back and request the 1.590" version. A discussion with Mike Bender in Tulsa, OK confirmed my suspicion that the 1.625" main is too big.
So the bottom line is that I should probably return the one they sent and request a 1.590" version(?)
Stanfield & Terrell in the Outback north of Escondido still do babbit jobs. If somebody else doesn't have their #, I'll get it.
The dimension between the main bolts in the block is 1.750”.
Boring the mains out to 1.700” would leave .025” of cast iron between the main bolt holes and the bore for the crank with out babbitt. Installing a Scat 1.590” crank would let you finish the bored babbitt and have a bearing thickness of 0.5475”. That is if the boring equipment is set up perfect, not all of Fords blocks were created equal.
Using the same 1.700” bore for the mains before babbitt would end up with a bearing thickness of 0.3675”, with the 1.625 Scat crank. You could pick up additional thickness by boring the block mains out to 1.750”, which has been done and shouldn't cause problems if the babbitt is properly poured in the block.
The answer to the question is both would work, I am sure the larger of the two would have more strength.
Giving more thought after our phone call, you could save yourself some freight cost by going ahead and use the crank you have.
Attached picture of block bored to 1.700", extra anchor holes and plugged for a pressure oil system.
I have used crankshafts 1.625 mains and others that only had a .010 -.020 regrind done on them and also never had any problems. The bigger of the two shafts (1.625) will work just fine.
Mike, that bloody decimal point did a jig on you. I cant imagine whitemetal bearings being more than 1/2" thick!
Allan from down under.
Yep decimal point got me. Maybe that's why this square peg don't fit well in a round hole. Also might be fussy math.
Mike - Thank you very much for all of your input.
Being a cautious man, I think I will endure the nuisance of exchanging the 1.625" crank for a 1.590" crank. Lang's does not even carry the 1.625" version because of the bolt hole problem. I think the 1.590" main will be strong enough for my version of a speedster. Three other engine guys as well as Lang's weighed in with that choice.
No reason in the world not to use that crank.
Bore the block to 1.750 and get on with it.
I used the Scat 1.625" crank with no problems. I did what Dan suggested and bored the mains out to 1.750".
When the block is bored to 1.750" there is room for.0625" thickness of Babbitt which is what I have measured in stock T blocks.
Also there is a lot of additional work and cost involved to fit a stroker crank in a T engine other than fitting the mains for a only small amount of gain in performance. Until the Scat crank became available the main reason to use the A crank was for durability. Now it may not be worth the effort in most cases.
Did you consider using the Onan bearing shells for the main bearings? Having ridden in your car I am impressed with how nice it runs and how well it pulls the hills.
When I have installed a crank with 1.625" mains I have always "dowelled" the main caps so I can get a precise fit and a uniform bearing material thickness. I have found that going with bolt sleeve (5/8" tubing) dowels is quite easy to do.
What I like about the big mains is the extra torsional rigidity.
I stayed with the cast Babbitt bearings because they supposedly are better at handling the dirty oil typically found in a splash system T engine. Also they are supposed to tolerate more crank flexing and misalignment than inserts. With the stiffer crank that may not matter.
I think with large journals and a filtered oil pressure system inserted bearings would be fine.
I agree with your desire for larger mains for stiffness if you are adding lots of horsepower.
The only objection I see to using the dowel sleeves is the main bearing diameter would need to be reduced since the distance between the holes is 1.750". Would it be possible to install dowel pins next to the bolts instead? The dowel pin holes could be easily matched drilled through the caps into the block for perfect alignment. Wider caps may be needed for that approach.
Scat is now making A rods that use inserts. Check out their web site. They sure look good.
I will try to post a picture of my approach. It works OK with the 1 5/8" main bearing. I need to check though as maybe I used 9/16" tubing which probably worked better. I did this 10 years ago so the memory sometimes gets fuzzy.