|
How do I fix this?? 5 Attachment(s)
You may recall a while back I posted about issues with the main bearings on my Scat 221 4" stroke crankshaft. I fixed that little problem, posted on here, advised Scat; they didn't want to know!
Well, during a mock up assembly yet another problem has surfaced. I honestly don't know how to fix this.....Look at the photos; these are shots of numbers 1 and 5 cylinders. No, the rods are not bent; they are NOS 21A conrods. The crankpins on the crank have been ground on a different centre to the cylinders, consequently, the rods are hard over one side. I cannot run it like this; what to do? I know what I'd like to do with that crank, and it wouldn't be pretty!! |
Re: How do I fix this?? Brian no pictures showing. Gary
|
Re: How do I fix this?? Need to post the photos.
|
Re: How do I fix this?? showing up ok here-- what does Scat say /
|
Re: How do I fix this?? They're showing up now.
|
Re: How do I fix this?? Is Scat one of those Chinese made cranks?
|
Re: How do I fix this?? Gary, on Long Island, only chooses Eagle crank, and Scat rods. Only, other wise too much modification for clearance, and balance. Sorry, you are in a jam.
|
Re: How do I fix this?? "Is Scat one of those Chinese made cranks?"
Definition; scat3 skat/ noun noun: scat; plural noun: scats
Origin https://www.fordbarn.com/forum/data:...BJRU5ErkJggg== 1950s: from Greek skōr, skat- ‘dung’. Which means it is SHIT!! |
Re: How do I fix this?? Hi Brian, difficult to tell from the photos without actually having the unit in front of you but it appears the crank is not located correctly front-to-rear in the block??
If you look at all the rods are they all "off" in the same direction, is it right and left banks, or is it random?? The "fix" to at least that problem to make it work isn't that difficult but the rods and piston must be separated. You could "side-grind" the pin ends. We do this occasionally on the belt sander! You just need to be real careful not to "upset" the pin bushing! Thanks, Gary in N.Y. P.S. What exactly was the main brg issue??? We don't use Scat cranks (for other reasons) but we do use their rods. This isn't your issue though. |
Re: How do I fix this?? Here is Brian's earlier problem with the crank...
https://www.fordbarn.com/forum/showthread.php?t=226600 Lonnie |
Re: How do I fix this?? [QUOTE=GOSFAST;1559751]Hi Brian, difficult to tell from the photos without actually having the unit in front of you but it appears the crank is not located correctly front-to-rear in the block??
If you look at all the rods are they all "off" in the same direction, is it right and left banks, or is it random?? The "fix" to at least that problem to make it work isn't that difficult but the rods and piston must be separated. You could "side-grind" the pin ends. We do this occasionally on the belt sander! You just need to be real careful not to "upset" the pin bushing! Thanks, Gary in N.Y. Why do you think this happens? Crank or pistons? Lonnie |
Re: How do I fix this?? Thanks,
Gary; to try and answer your questions; There is a definite pattern, inasmuch as all conrods are closer to the rear of the piston boss. The worst one is as pictured, cyl's 1 & 5, where the clearance is 0.020" at the back. How much is the least amount of clearance I could get away with? I could ,as you suggest, grind a bit off of the small end, but, Geeze, I shouldn't have to! I think I can get away with all the other cylinders; minimum clearance on the rest would be 0.080". Lonnie,: this is definitely a crank issue. Incidentally, the pistons I ordered as specials from Ross, 4" stroke 3 3/16" bore flat tops. Same as 49-53 Merc but with flat tops not domed. It wasn't until I went to do the initial mock up, that I realised they hadn't machined inside the gudgeon bosses, and the conrods wouldn't fit. I was at work until midnight last night machining the required clearances. I notified them of their oversight, they said 'sorry'. At least that is a [ever so slightly] better response than I got from Scat when I told them about the main bearing issue. I need to follow Tony's suggestion from that earlier thread, I am over building these old things!! Too much agro, things were so much easier when I was young and knew nothing!! |
Re: How do I fix this?? There is an advantage to "knowing nothing", you never have to wonder what you forgot...
|
Re: How do I fix this?? Quote:
Quote:
On a side note, this is an issue that wouldn't even be noticeable with the H-beam rods, the rod eyes are a bit narrower than the OEM ones! Anyway, "Good Luck" with your fix, should be OK in the end! Thanks, Gary in N.Y. P.S. About 15 or 20 years ago we got an $1800.00 4340 Lunati BBC stroker crank in the door for a build. When I first removed it from the box the rear thrust flange "wall" caught my eye, it looked overly thin. Layed it in a block with some brgs and EVERY counterweight side was hitting the main webs, crank was too far forward in the block. Lunati asked no questions (we knew Joe really well), sent a replacement with a "call-tag", and took care of it all. The crank was definitely "defective"! The rear thrust is the "datum point" for the crank machining, it determines where the rest of the crank sits front-to-rear in the block! |
Re: How do I fix this?? Brian , Mike at H&H built an engine similar to yours earlier this year using the same crank as you. I believe he used the Scat rods also & that would possibly overcome the situation you have right now. He did tell me that a few other mods had to be made to the crank to get it to work in block . I am not sure what but did tell me if I purchased one of these cranks he would tell how to make it work & that it was no big deal. Maybe it would be worth a call to Mike .
Cheers Tony |
Re: How do I fix this?? Why would you buy a crank knowing it was not right and would need to be modified?
|
Re: How do I fix this?? Quote:
|
Re: How do I fix this?? None of the conrods are centred in any of the pistons. The worst 'set' is as I pictured, with only .020" clearance. I still have the milling machine set up from when I machined the piston bosses, so could take a bit more off of the two pistons on one side, alternatively could take a bit off of the side of the small end of the conrods. Which would be preferable? I ask again- what is the minimum side clearance required?
|
Re: How do I fix this?? Quote:
Having said that, if you're going to make a correction just take it right to .060". Thanks, Gary in N.Y. P.S. During the course of working with almost ALL crank mfr's, from the budget pieces (Eagle/Scat, both Chinese) up to the "Made-in-the-USA" high-end ones, we see many pitfalls with most. Recently had one hell of a time balancing a fairly expensive Crower shaft. Ended up welding our own flange to the existing flywheel flange on the Crower. I called out there and really complained, they didn't care at all and said "if you don't want the crank send it back". Definitely not fair to the end customer?? |
Re: How do I fix this?? Hi Gary, Thank you. It is morning here, I've thought on this and decided I'd machine another .040" off the one boss of each piston to give me a .060" clearance. Just came on here and you've verified that figure, so thank you!
Knowing now what I do, I'd have been better off in all respects if I'd purchased a genuine 49-53 Merc crank, and machined it to suit my early block application. Hindsight, ain't it great?!! |
Re: How do I fix this?? The fact that the piston C/L is offset from the rod C/L would concern me. Seems there would be forces cocking one side. Eventual problems. I could be wrong.
|
Re: How do I fix this?? Yes Tony, it is a concern.....and I agree with you. What I've done will enable it to work, but I don't like it!
|
Re: How do I fix this?? hot rod model T guys have been putting model A cranks into the T,s for decades. when you do this the result is like brians problem, the holes dont center on the rod journals. so, like brian they run the piston off center. seems to work, however my guess is these are high performance engines that are not trying to set a record for high mileage. best wishes brian, i know you like your 21 studders !
|
Re: How do I fix this?? Thank you cas3, didn't know that. Good to know. Should make me feel better, but it don't!! lol
|
Re: How do I fix this?? Geez Brian ,I was going to get one of those cranks.to use in a 36 block,I think I,m better off using another 99a block.
What piston clearance will you use with the ross pistons( assume they are forged) Could you measure the centres of the crank pins on the crank and compare those to the bore centres ,just o know where the error is . Lawrie |
Re: How do I fix this?? Lawrie, If you want a 4" stroke in your 36 block, trust me, your best bet will be to get a genuine Merc crank, reduce the main journals to 2.399, and widen the front and middle journals to suit the 36 block. You'll need to make a spacer for between the front main and timing gear to locate gear in correct spot. Shorten the snout and turn down to 36 size [not essential- you could probably run the later pulley[s]]
I don't know if 99A/8BA rods will clear block, but if you're boring to 3 3/16, you'd probably be able to run those which would eliminate grinding rod journals down to 2". Only other thing would be the absence of the slinger for rear oil control, but I think Reds Headers has a seal conversion to fit 36 rear main, so you'd have positive oil seal control. Ross instructions call for .004" clearance The centre to centre errors for the three rearmost cylinders was around 0.5 - 1.0 mm [.020" - .040" The front cyl's centre /centre error was around 2 mm [.080"] |
Re: How do I fix this?? if you have to cut the journals down to 36 size, could'nt the crank grinder grind them to the location you want?
|
Re: How do I fix this?? Brian ,I think I will stick with a 99a block when I need to get the larger displacement,
But will do an engine change out on the 34 in the next week or so,I,m fitting the nicest smoothest engine I have,the original 33 babbit engine with sts bore and those little skinny rods with flat top pistons. I have a standard bore 37 block that would be a good exercise though. You have any hair left,LOL Lawrie |
Re: How do I fix this?? cas3, The 36-38 221 cranks run 2.399" dia mains, but the front and centre journals are longer than the subsequent 39 on cranks with the 2.499" dia mains. When scat manufactured this piece of scrap iron, they ground to the smaller journal size, BUT used the later bearing widths [too narrow]. So, in order to primarily get the crank to fit a 21 stud block, I had to widen those two journals. If I had have used a genuine 255 crank, I would still have had to have modified those widths [and dia's]. The positioning of the thrust faces determines everything else.
So, not only did Scat bugger up the mains, they also referenced the positions of the conrod journals in regard to the thrust faces incorrectly. |
Re: How do I fix this?? Quote:
Take a picture of all 3 mains, at right angles with the crank in the block, with caps, so I can see where the crank has come out, for position. Then, you said, No, the rods are not bent; they are NOS 21A conrods. " END QUOTE " Did you check the rods for Alignment, or are you assuming, that they are straight, because they are new in the box. If you are, being new does not mean a thing. Every rod that is put into an engine should be checked for alignment! Twist ,Bend, and Off Set. Your pictures clearly show Rod Off Set. That can be caused, By the Rods, Crank set wrong, Crank made wrong, Cylinders Bored Off, Ect. Have you Checked the Scat crank Measurements, against a Ford crank? Herm. KohnkeRebabbittingService.com |
Re: How do I fix this?? Herm, you are so right! Of course the rods were checked for alignment. And I can fit any rods on that journal and have the same offset. Block was a virgin unbored block, now bored to 3 3/16 on the exact centres that it came from the factory with. A new head gasket locates nicely around all cylinders.
Comes back to only one scenario you mention doesn't it? Incidently, surprise ,surprise, Scat don't want to acknowledge this. They don't recognise what sort of rods they are; they don't look like Scat rods! Which is a damn good thing!! |
| All times are GMT -5. The time now is 12:18 PM. |
Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2026, vBulletin Solutions Inc.