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Discussion Starter · #1 ·
Hi Guys,

I started assembling the sealed power hyper pistons/scat h beam rods onto my scat 393 stroker crank only to have my enthusiasm seriously dampened. When I turned the crank to check for clearance etc with number 1 piston installed the bottom edge of the piston skirt fouls on the crankshaft counter weight. I also tried with number 5 piston & this also fouls on its respective counter weight. In addition to this I also positioned number 1 & then number 5 rods as close to the closest cam lobe & they also foul!!

Therefore I have two questions which hopefully sombody can help me with:

To get round the piston skirt clearance problem I believe I will have to grind the area using a die grinder & rotary burr/stone of the skirt that fouls on the counter weight. Being a V8 virgin, (but a reasonably competent mechanic) can anyone advise what is the best way to go about this? Will I have to weigh the pistons to ensure I match the weights of the opposed pistons, (ie 1 & 5) with regards to balancing. What clearance do I need to aim for?

The second question, (& hopefully not a dumb one!) is can you only check cam lobe to rod clearance accurately when you have your timing gear hooked up & the cam/crank in reasonably correct phase? If I do have a lobe to rod clearance problem what are my options, (cam is a hydraulic flat XE 284) will I have to grind the rod or is it better to change the cam?

I find this pretty frustrating as I would have thought a complete scat stroker kit would not have clearance issues as the parts would be pre-checked for clearance!?

Any help/information would be highly appreciated.

Regards,
Martyn
 

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Dont Grind anything!!!
Send that set back and tell them to give you the right setup.
You shouldnt have any cam lobe clearance issues if you have the right Kit.
good luck
 

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Sometimes there WILL be clearance issues. Some pistons have longer skirts than others, and need ground until they clear the counterweights. Just be careful not to leave any burrs that will scratch the cylinder wall. The amount you will probably need to grind away should not have a significant effect on the balance job... assuming this is a sub 6800 rpm engine. You'll want to shoot for around 0.060" clearance.

As for the rod to camlobe clearance, you'll NEED to do that with the timing chain correctly installed. 383 stroker small block chevy's have this problem, and the offending rod generally needs a little grinding to clear. However, I doubt your will interfere once the timing set is installed.

Good Luck!
 

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I agree with 71hotrodpinto--send the pistons back. Some pistons have larger skirts than what is needed and are not friendly with big stroker parts.

I used the Scat crank/h-beam rods for my 393w. I used Probe Pistons and had no interference with them nor the cam lobes. The only thing that I had to clearance was a couple of places on the block's oil pan sealing area (primarily around the pump) and I did remove a little material from the bottom of a couple of cylinder sleeves. Very little grinding overall and none was needed on the moving parts.



_________________
Dennis

65' Stang

393 Stroker, Toploader 4 spd, 9" 3:70 rear.

Victor Jr. Knockoff Heads, 282S cam, Stealth Intake, Bigs Stage 5 750DP, Accufab Headers, Scattershield, Caltracs.



<font size=-1>[ This Message was edited by: dennis111 on 6/5/06 1:58am ]</font>
 

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There ARE pistons out there that were designed AFTER 393's became popular that are built with the skirts shortened to clear applications like yours, but many 302 pistons aren't made that way. Grinding the skirts a bit to clear the crank won't hurt a thing. It's frustrating, but it won't hurt anything.

For the uninformed a 393 is built using an aftermarket crank, 351W length rods and 302 pistons. It's the cheapest way to get big cubes out of a 351W.
 

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The SpeedPro hypers have a fat skirt. They are designed for a 302 where there is plenty of clearence.

I had the same interference on a 398 I built a few years ago. (Scat/SpeedPro)
I used a sanding roll to remove the material. No big problem, just takes a little time.
 

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I had crank interference problems but the counterweights were hitting the on land right under the pin, not the skirts. Some of these chinese cranks just need to have the counterweights ground. Make sure to rebalance.

Fords almost never have rod to cam clearance problems, most just small block Chevys.

_________________
77 Maverick
69 Mustang Fastback 393



<font size=-1>[ This Message was edited by: MaxPower on 6/6/06 9:27am ]</font>
 

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What Part of Yorkshire are oyu in Martyn? NOrth, South or West?

FE
 

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Discussion Starter · #11 ·
Thanks for the input guys, particularly Mike - thanks again for the sound advice.

I am based in South Yorkshire, England.

I am still waiting for a response from Scat so will keep you posted. As Mike has pointed out, as I am living in the UK the implications of returning things back to the US is horrendous, (import/export duty VAT, P&P etc), so I am trying to avoid that. However I will still pursue Scat as in my opinion they have supplied components unfit for purpose.

I will keep you informed as things progress & no doubt I will be calling on your experience as my build progresses!!

Martyn.
 

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Good Luck Martyn!
I lived in North Yorkshire for 3 years.. Up near Harrogate at Menwith Hill, you may have heard of it... Anyhow, Good Luck with the build!
 

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On 2006-06-06 12:57, martynUK wrote:
Thanks for the input guys, particularly Mike - thanks again for the sound advice.
(snip)
I will keep you informed as things progress & no doubt I will be calling on your experience as my build progresses!!
I've always found N20Mike's advice well founded. In this case I would encourage you to heed it and pull out the die grinder and fit the cartridge roll and work on the assembly. While it is a "kit" a 393 crank is not specifically designed for that 302 piston. KB makes a piston designed to work and it has a shorter bottom half. I helped RPM build his 393 and he used the Scat crank, 351W rods and the KB piston and it was hunkey dorey.
On the cam clearance, it definitely can only be checked with the timing gear in place. I built a 4.14" stroke 422, a CC274 cam with worked over Chrysler rods and had to "clearance" the rod bolt heads. Wouldn't have been an issue with capscrew rods and certainly don't think it'd have been a problem with a 3.85" stroke.
Grind the clearances and then balance all 8 pistons to within a gram.
Cheers!
 

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Just get grinding, grab a beer and take your time. Not an issue
 

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I had to do some minor grinding on the front counterweight of a 393 Scat crank to clear the oil pump. Not a big deal if you have not sent the crank for balancing yet.
 
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