Re: Stock main caps ?

jason November 26th 2011, 12:46 am

Lem Evans wrote:
"2-bolt, filled block , girdle ......about 750 plus 150 of nitrous"......Like has been said....'how many passes?'
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I would not call be bearing "good" although it's not in trouble yet. The front part of the bearing shows a good deal of wear and the rear about none. Taper in the block's housing bore or taper at the rod journal....flexing of the block or crankshaft.

sorry I missed where you said how much power you were making . The bearings look better than the ones in my 302 , but I do see now what you were talking about, engine building isn't my strong point , I can tune good enough to keep it together .

cool40 November 26th 2011, 12:50 am

cap walk.

the left side you can see the black spots where the action was.

Barney November 26th 2011, 1:35 am

At that hp level you should be fine, even spraying it occassionally. I leaned on my stock shortblock pretty hard and sprayed the snot out of it. Will there be cap walk? Yep. Will that be the end all beat all? Probly not. If you rattle it, the party will be over though.

Lem Evans November 26th 2011, 1:35 am

Caps can do walk/flex.....I'm more concerned about what the bearings look like....up to the point that the block or caps are not broken.

One bolt mains seem to work real good ....the 1st time I saw the crack from the #2 main bolt hole to the cam tunnel was interesting. I removed the oil pan to find one of the #2 main bolts in the pan. The engine came to me for a seemingly unrelated matter.

Edit: I mis-spoke, it was the nut from the main stud that was in the pan....not a bolt.

Doug Rahn November 26th 2011, 6:52 am

Baitshop wrote:^^Either that or someone got a little happy with the silicone, causing the cap to sit cockeyed.

IMHO the silicone didn't case the cap to sit cockeyed. The machined mating surfaces of the block and cap did not match, fitting tight at the bolts and a gap at the seal thereby creating the tapered bore Lem spoke of and no wear at the back of the bearing.

jason November 26th 2011, 8:14 am

Why are bolts preferred over studs when it comes to cap walk? With a 521 Im thinking I shouldnt have to turn it much over 6,000 . I'm trying to find all the little tricks to make it strong and reliable .

Baitshop November 26th 2011, 9:26 am

Pardon my ignorance here, but look at the amount of silicone on the cap in question. There is a mountains worth at the back of the cap and none at the front. You really don't think that it could be that simple? I never put silicone on rear mains prior to cap installation for that reason. I guess I've never measured to verify, but wouldn't any amount of shit between the cap and block affect clearance, yet alone a big pile at one end like in the picture? Seems pretty simple to me.

bruno November 26th 2011, 9:31 am

Baitshop wrote:Pardon my ignorance here, but look at the amount of silicone on the cap in question. There is a mountains worth at the back of the cap and none at the front. You really don't think that it could be that simple? I never put silicone on rear mains prior to cap installation for that reason. I guess I've never measured to verify, but wouldn't any amount of shit between the cap and block affect clearance, yet alone a big pile at one end like in the picture? Seems pretty simple to me.

yep doesn't make any sense ...i didn't build that engine , it was the one that came with the car at the time , but why would any one want to put silicone on the edge of the cap like that ? would make for a very un even mating surface

QtrWarrior November 26th 2011, 9:32 am

I'm going to assume some things here..

IF the silicone was not set up when the cap was torqued down... Don't you think it probably "squeezed out" as the cap was tightened ?? If so, how thick could have possibly been ??
The piling up was probably a result of pulling the cap off...

Doug Rahn November 26th 2011, 9:45 am

My point being, with the high clamping load of the main bolts and RTV silicone not being that dense, one or both machined surfaces where not flat, leaving a very small gap at the back of the cap.

Paul Kane November 26th 2011, 1:06 pm

bruno wrote:2-bolt, filled block , girdle ......about 750 plus 150 of nitrous

Without knowing the details of the build (from bearing clearances to tune and everything in between), no-one can draw a 100% conclusion as to why the bearings or caps look the way they do. Could be a 0.0015" main clearance on the rear bearing, bearing taper, main bore taper, crank flex from that aftermarket crankshaft, this or that.

Frankly, I don't think that looks partiularly alarming for a 900 hp drag racing engine using 2-bolt caps with main studs. An "adjustment" from this observed point is easy enough and you could get a little more life between bearing service.

Paul

Paul Kane November 26th 2011, 1:13 pm

jason wrote:I would have never thought stock bolt are less likely to walk than studs , why is that ? And do I get new bolts or use the originals ?

It's a long story, has mostly to do with the design of the aftermarket main studs that are made for the 385 Series.

Another post from another forum:

Paul Kane wrote:The very fact that they are non-reduced shank seems to be the actual problem, not a strong point. It prevents the fastener from properly stretching during installation. The only place those studs yield any meaningful amount is at the minor thread diameter of the coarse thread (that's the smallest diameter of the straight-shank main stud), which is in the block's main webbing. And that section of stud is not a continuous, necked-down length of fastener. And so the stud performs inadequately.

Main caps don't show walk so much from moving up-and-down (in line with the main fasteners) as they do from being momentarily yanked inward toward the main journal. That's why the 18-degree splayed main caps minimize the walking so effectively (they counter the inward yank because the fastener loads the cap in the opposite direction, so to speak). Yes, better fastener retention helps prevent walking, too, and I think that the OEM necked-down main bolts do a better job by virtue of their design/retention capabilities than the straight-shank main studs.

Go grab your ARP catalog. If you look at other ARP fasteners, such as their rod bolts, you will notice that they have a reduced shank. ARP used to offer a Pro-Series main stud that was necked down. Don't know if they still do or not because I haven't checked in awhile since we rarely use main studs in these engines. But I am aware of others who have had better results with the Pro Series necked-down main studs than the straight-shanked versons (both stud types tried in the same engine). As for me, I am fan of the OEM bolts over the straight-shanked main studs.

Paul

87GT November 30th 2011, 4:50 pm

Also would the saving grace/ help of the aluminum rods reduce the cap walk as well?

the Coug November 30th 2011, 5:58 pm

87GT wrote: Also would the saving grace/ help of the aluminum rods reduce the cap walk as well?

Aluminum rods do one thing they hold the pistons in place without them they would not be connected to the crank.....

87GT November 30th 2011, 7:05 pm

So you would not be able to push a stock block / cap set up a little harder by using lighter aluminum rods-rotating assembly, As compared to steel h- beams? Before cap walk?

the Coug November 30th 2011, 7:16 pm

87GT cap walk is when the crank tries to push it's way thru the bottom of the main cap, it Flexes out so in turns it brings the sides of the cap inward. you with me so far? ok you can cure this by, Installing main cap straps and milling off the main cap level with the main bolts... or put on 4 bolt main caps. the use of regular main bolts help a hell of a bunch... I do not like main STUDS because I feel they are weeker than the Factory bolts and some on here agree. and NO MAIN GIRDLES DO NOTHING other than relieve you of pocket cash PERIOD.... ok so now we are on the same page. Rod just hold the pistons in place the only advantage to aluminum is lighter, and replacement is alot sooner than steel rods....The Block is way stronger than you would think......I feel if you put 4 bolt mains on it or good main straps you and exceed 1000 hp with ease, and i don't think you have to pour it full of concrete either I feel that just adds weight, it does nothing for ridgitity, if the cylinders are soniced and have enough meat it should be good. no need for concrete.....

Paul Kane November 30th 2011, 7:56 pm

87GT wrote: Also would the saving grace/ help of the aluminum rods reduce the cap walk as well?

Generally, I would think that a lighter rod made of a more absorbent material (such as aluminum rods) might offer some reduction of the forces being sent to the main caps. So in most cases, aluminum rods can play a part in minimizing cap walk.

Paul

Lem Evans November 30th 2011, 8:59 pm

Paul Kane wrote:
87GT wrote: Also would the saving grace/ help of the aluminum rods reduce the cap walk as well?
Generally, I would think that a lighter rod made of a more absorbent material (such as aluminum rods) might offer some reduction of the forces being sent to the main caps. So in most cases, aluminum rods can play a part in minimizing cap walk.

Paul

"If" less force is applied to the crankshaft the result would be less tq/hp.

Paul Kane November 30th 2011, 9:59 pm

Lem Evans wrote:
Paul Kane wrote:
87GT wrote: Also would the saving grace/ help of the aluminum rods reduce the cap walk as well?
Generally, I would think that a lighter rod made of a more absorbent material (such as aluminum rods) might offer some reduction of the forces being sent to the main caps. So in most cases, aluminum rods can play a part in minimizing cap walk.

Paul

"If" less force is applied to the crankshaft the result would be less tq/hp.

I don't think we're talking about tq/hp, I think we're now discussing steel rods versus aluminum rods. Besides, how much less power could a lighter aluminum rod take away from a heavier steel-rodded engine?

To clarify my statement quoted above:

Generally, I would think that a lighter rod made of a more absorbent material (such as aluminum rods) might offer some reduction of the forces being sent to the main caps. So in most cases, aluminum rods can play a part in minimizing cap walk assuming two engines producing the same power but where one is built with steel rods and the other with the aluminum rods.

Lem Evans November 30th 2011, 10:02 pm

Maybe you are looking for the word "shock' and not force.......I'd still disagree but......that's my opinion.

Paul Kane November 30th 2011, 10:14 pm

In this case, "shock" is a kind of "force." So same page there; again me being more general and you being more specific.

So you don't believe aluminum rods can reduce cap walk? And/or, you believe they will measurabley and substantially hurt overall engine output compared to the steel rods?

Or...are you saying that you'd take the cap walk (etc) over the "substantial" power loss? And if so, where would you draw the line (how much cap walk (etc) does it take for you to eventually opt for the aluminum rods)?

richter69 November 30th 2011, 10:25 pm

those pics Nick put up, that was an aluminum rod deal.

Paul Kane November 30th 2011, 10:29 pm

richter69 wrote:those pics Nick put up, that was an aluminum rod deal.

And how did it compare when the engine had steel rods in it?

I already posted about those pics on page 3...

Lem Evans November 30th 2011, 11:16 pm

Paul Kane wrote:In this case, "shock" is a kind of "force." So same page there; again me being more general and you being more specific.

So you don't believe aluminum rods can reduce cap walk? And/or, you believe they will measurabley and substantially hurt overall engine output compared to the steel rods?

Or...are you saying that you'd take the cap walk (etc) over the "substantial" power loss? And if so, where would you draw the line (how much cap walk (etc) does it take for you to eventually opt for the aluminum rods)?

1] I do not believe aluminium rods reduce cap walk.
2] I believe force makes the crank rotate.
3] I never said that I'd 'take' cap walk "substantial" or otherwise...do not put words in my mouth.
4] I draw no lines.
5] I do know that the high end aluminium rods cost about 1/2 as an A460 block.

Lem Evans November 30th 2011, 11:18 pm

Detonation is also a "force".

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