Cross tied main cap

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What is strange is the KB block has steel caps. Kinda the reverse of what Monte was talking about.

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KB gives you the option of steel or aluminum main caps when you order a block.

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The reason the girdles help, is because when the piston is at (or near) TDC, the rod is trying to push the crank out the bottom of the block. The majority of the is held back by tension of the main sadles. But if we look at the #1 rod as an example, there is more then just tension in the main sadle. The bending moment of the crank at the #1 cap tries to bend forward, and the #2 cap goes rearward. It’s this flexing forward and rearward that can contribute to the bulkhead breaking above the main caps.

Think of it this way… if you had a pretzel stick, and you tried to pull it lengthwise, it’s fairly strong. But if you bend it, it can easily crack. That “Bending” is exactly how the block acts. Cast Iron is not very good at “bending”, so it can lead to cracking.

Here are some pictures to explain this “bending” is happening. This is a picture of my main bearings from the last time I took the motor apart (small block, but it makes the point). On the inside edge of each main bearing, ONLY in the area opposite of each cylinder (not all the way around the edge), you can see where each main bearing was wearing. This is because the cap and crank were actually bending forward on the compression stroke!

I don’t think any of us could say if removing material from the side to add cross bolts is a trade off worth doing. It would certainly help the cap from wagging front to rear, but at what cost to the block? The girdle however would give you the benefit without a doubt.

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I disagree on your thoughts on the crankshaft trying to push the main caps forwards and backwards by bending the crank on the firing stroke, if that was the case the thrust bearings wouldn't last would they Also when the motor is firing on the power stroke the rod is pushing the against the cranksahft at or around 30 to 45 degree sideways trying to push the crankshaft mains out towards the oil pan rail, not straight down or forwards or backwards in the main saddles, correct Metal transfer(fretting) from the block to the main caps is usually cause by detonation from a bad tune up, it can be RPM related also Most failures in race motors are caused by some part being overstressed or a flaw in the metal or machining in my opinion

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Big blocks have a tendency to "fret" the caps, which means the caps "bounce". Has nothing to do with bending of the block. Its all about clamping force. When the caps bounce the webs take the brunt, because the crank IS hammering the caps and webs. Attempting to "lock down" the caps with a girdle, forces the webs to take ALL the pounding and they simply are not strong enough in a stock block.

The pic you showed, from a small block, could be a number of things. Maybe the main housing bores are not perfect. The caps could be moving and "egg" shaping the hole, which would result in what you are showing. Could be crank flex. A big block usually shows bearing wear at 6 and 12 oclock on the bearing, when you are hammering the caps and fretting them..............At least the SEVERAL I broke looked that way. And the fretting is not always caused by something being wrong, as in tune or rpm. Sometimes it is simply POWER and more of it than the general design can hold

Monte

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I disagree on your thoughts on the crankshaft trying to push the main caps forwards and backwards by bending the crank on the firing stroke, if that was the case the thrust bearings wouldn't last would they Also when the motor is firing on the power stroke the rod is pushing the against the cranksahft at or around 30 to 45 degree sideways trying to push the crankshaft mains out towards the oil pan rail, not straight down or forwards or backwards in the main saddles, correct Metal transfer(fretting) from the block to the main caps is usually cause by detonation from a bad tune up, it can be RPM related also Most failures in race motors are caused by some part being overstressed or a flaw in the metal or machining in my opinion

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Funny you mention the thrust. The center main cap/bearing on mine was the ONLY one that didn't look like this. The thrust face however didn't look very good, which leads me to believe that the thrust WAS taking all of the abuse from the cap moving around.

Force on the mains is most definitely at TDC. See the attached pic... this is force vs. crank rotation of a main bearing. Notice that there is a peak pressure curve on each firing point near TDC (Red circles). The crank has very little bending moment on it as it rotates to 90 degree's because most of its energy is rotating the crank. Not to mention the pressure is SIGNIFICANTLY lower at 90 degrees. Thrust force on the cylinder wall is a different story though.

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Monte,

I agree with your analysis of the how the crank moves, however I dis agree with the not using a girdle. you don't want your caps to bounce as that adds a lot more stress to the webs as the stud threads are always pulling at the main webs and they act like an impact hammer. the girdle is there to help clamp down the caps so the caps are not solely relying on the main studs to hold them down.

since different caps are experiencings forces at different times in the rotation of the engine it makes sends to tie the caps together and to the oil pan rail of the block so the loads are more distributed. will it be even? nope. but adding and distrusting stresses and load to areas of the block that aren't being used, like the oil pan rail. will take some of the load away from the main webs.

will adding a girdle never fail a block? nope, but it will give it the best chance to survive more abuse.

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Well, you all have good points, here's what I have observed. My SHO motor, 3 liter 8000 rpm engine, was designed by Yamaha to take at least 300 hp. It has a really solid cast iron block. It ALSO has a main cap girdle, in this case it's cast iron and only ties the main caps together fore and aft.

I have a lot of respect for Yamaha engines, they are usually pretty tough. So when I see a factory main cap girdle from them I have to believe it adds strength to the engine.

The block for this motor which is only 183 cubic inch V6, weighs almost exactly 100 lb. So in pounds per cubic inch it is ahead of a 500 cubic inch bigblock on which the stock bare block weighs around 230 lb.
So if a main cap girdle helps the stouter block, what makes you think it wouldn't help the weaker block?

I am not trying to explain what it does, it's kind of a mystery to me. But it seems to do something.

R.

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Is that Yamaha set-up not more of a bed plate than a girdle, as in the mains are all one piece? If so I would think it would be structurally superior to the girdle in that it is designed to handle the vertical force that the flat plate girdle can't.

Kevin

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I have to jump in. I never used a girdle. I never used aluminum caps.
I used old time circletrack cap straps. Early in the life of this build, I was learning the ins and outs of engine tuning. Nothing gives an indication of your tune like the caps. As previously alluded to, similar metals when moving against each other will exchange material and show positive evidence of movement. If you are seeing this, expect failure. You are exceeding the clamping limits of the structure. The peppering on the mating surfaces tells you that the timing is happening to early for the engine. That being said...If you are not seeing it with a factory block, you aren't making all the power you "unreliably" could.
With a naturally aspirated engine, you are limited in the WAYS you can make power. I understand the often thrown around hp limits of factory blocks. I think the generally accepted 750 hp number for a stock block is a bit on the low side, but I'll roll with it.
Getting into turbo apps, throw that number right out the window. A properly(in my head) tuned turbo engine will reliably exceed 1000hp. I was seeing cap walk early in the life of my 470. I was sticking to closely to commonly accepted timing curves. After listening to people with a lot more experience than me, and piecing clues/evidence/info, I started doing my own thing. I would say, any real experienced dyno tuner would easily get more power with less boost out of my engine, but never with the reliability I got out of it. I've had guys nudge me to put timing in the thing, (a couple of degrees could be 60hp) The engine made low hp for what it was, but it was dead reliable.
I'm rambling. Here's my bottom line. Hp limits on caps/ blocks are directly proportional to the WAY you make the power. I get the feeling that aluminum caps give a false sense of security because of the missing evidence of movement on the surface, but I do agree that they are a better/simpler choice then using factory caps. The loss of evidence on the mating surfaces, had I used aluminum... would have lead me to a catastrophic engine failure for sure. I never would have learned the things I have about the tune up.
Take a look at the bottom end. Factory 400 block, factory caps with tool steel straps, factory crank. 1100 hp. Other than freshening every 2 years, rings bearings and wrist pins, the bottom end was together from 1992 until the time I sold the car in 2006. I'm NOT advocating the goofy straps I used. Just showing what you can get away with if you veer off from the "rules" of engine building/tuning.

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What kind of power did you get away with with a stock block and the alum caps? 750 HP is the usual limit that is talked about. How did the bearings / cap interface surfaces look after being thrashed? To me the used hardware tells the real story.

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The bonzi 8.80 ET is still short of 1100 HP. Once again HOW many passes were put on this combo? And how many were in the 8.80 range? I've gone 8.60's-8.80's with a stock non-filled no girdle engine at a MUCH lower weight and the block was cracked after 275 passes and was still running 8.60's before I took it apart for rebuild. Mine were also with the weaker 440 (RB) block.

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Wallace calculator puts 155 mph at 3700 Lbs as 1103 HP. 145 and 3700 Lbs calcs 903.

Kevin

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The bonzi 8.80 ET is still short of 1100 HP. Once again HOW many passes were put on this combo? And how many were in the 8.80 range? I've gone 8.60's-8.80's with a stock non-filled no girdle engine at a MUCH lower weight and the block was cracked after 275 passes and was still running 8.60's before I took it apart for rebuild. Mine were also with the weaker 440 (RB) block.

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Don't get upset. I cant give you documented, witnessed evidence of every teardown and pass the car made. "bonzi" run was one of maybe 20 runs in the 8s. The years before were (est 200- 300 passes) Oh yeah, driven to the track on pump gas/ mufflers. There is a really bad youtube video that shows probably 4 or five 8 second passes. I cant remember the link. search "trendz 8 sec"
So, what did you figure a car would have to make to go 155 at 3700 lbs?
Assuming I'm telling the truth(which you don't) Just takes me further into the belief in what I stated about how dependability is directly related to HOW power is made. I suggest turbos for the doubters

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Car weight was a touch over 3700 lbs with me in it, best et was 8.80 best mph was 155. 3.50 rear gear, torqueflight, 31"w tire.
admittedly, most of the cars life was making ets in the sub 9.20 range with mph always above 145. I spent to many years using to small turbos. The last year I owned it I stepped up the turbos and would go in the 8s without breaking a sweat.
Ive been on this board since the beginning of the build. If you want to research me and the car go ahead.

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Yeah. leave it to someone who thinks out of the box to do something out of the box.

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I thought i found the right video. That does run VERY good.

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Yeah. leave it to someone who thinks out of the box to do something out of the box.

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