Main cap girdle's....do they work??

[Freiburger]

Re: Main cap girdle's....do they work??

on a small Ford stock block over 500 HP they are good for keeping all the pieces in one lump when the block splits.

WHEN the block splits. LOL! Sad but true.

[dartman366]

Re: Main cap girdle's....do they work??

I looked at one on the internet for the BBM and it wasn't like that. That would be the best setup I would think.

You put in the studs on the mains and pan rail, dropped the crank in, and put the caps on, then slid little hardend steel spacers that took up the space between the plate and the main cap (and allowed for the main cap to need no machining) then the plate went on over the spacers , and then the washers and nuts. It was a 3/8" thick aluminum plate - which didn't impress me much. I hear someone else has a 3/8" or 1/2" steel plate.

the one for my smallblock mopar is the type that you speak of but it is made of steel and the one's for the bigblock's as far as I know are made from steel also and are 1/4 thick, the only thing I did different was to do a little extra machining on the cap by making all the spotface's for the main stud's all the same(the height's were as much as .025 different from each other) and then milled the flat on the cap a specific height and then made new hardened spacer's, I thought the spacer's that were sent with the girdle were kind of chinsey, I actually think it makes a good thing a little better.

[Falcon67]

Re: Main cap girdle's....do they work??

I can't speak about use on a Mopar, but on a small Ford stock block over 500 HP they are good for keeping all the pieces in one lump when the block splits. I rank them right up there with that valley girdle crap.

[RacerRick]

Re: Main cap girdle's....do they work??

I looked at one on the internet for the BBM and it wasn't like that. That would be the best setup I would think.

You put in the studs on the mains and pan rail, dropped the crank in, and put the caps on, then slid little hardend steel spacers that took up the space between the plate and the main cap (and allowed for the main cap to need no machining) then the plate went on over the spacers , and then the washers and nuts. It was a 3/8" thick aluminum plate - which didn't impress me much. I hear someone else has a 3/8" or 1/2" steel plate.

[milner351]

Re: Main cap girdle's....do they work??

Rick
in my limited experience
(arp studs, stock main caps, steel girdle)
you torque the main caps down with one set of hardened washers then nuts on the studs,
then you put the girdle on top of those nuts, and tighten them down with another set of hardened
washers then nuts on top of the girdle.

Where I ran into trouble was getting a stroker crank, H beam rods, steel girdle windage tray and oil pump pick up to all play nice inside the oil pan.

I think I know now why hamburger and others charge so much for their parts - they've figured all this out and got a system that works all together.

[RacerRick]

Re: Main cap girdle's....do they work??

I believe aluminum girdles would be better for dampening harmonics, as the aluminum would actually absorb some of the vibration because of how soft it is in comparison to steel. I don't like that you would be torqueing the mains through a relatively soft plate of aluminum.

Remember that the main studs are actually just springs held in tension that is lower than their point of deformation. The studs are always stretching a tiny bit and springing back as the engine is running. Its miniscule on an engine with fasteners properly designed for the application, but it is there. The better the material, the more elastic they are (will stretch farther and spring back) and the more force it takes them to stretch.

If you are really hammering on it, and the caps are trying the bounce because the forces are stretching the studs more than usual, I would think that the aluminum would would help to keep the caps from bouncing for a while, but would deform perminently around the head studs with each time the engines caps tried to bounce - loosening them.

This is just my theory.

I have been really thinking about a main girdle in my next BBM. If I get one, I would get steel.

[milner351]

Re: Main cap girdle's....do they work??

At the most simple - its a mass thing - as stated above - adding mass (ever seen weights hanging off a stock exhaust system?) changes the resonant frequency of the system.


What I DONT understand is aluminum girdles --- that just makes no sense to me at all.


Please tell me more about the sequence of torques --- say you're running studs - you follow the arp stud & nut tightening procedure and sequence steps.....

then you put the girdle on, and the next set of nuts to hold the girdle --- do you tighten those in the same sequence? How tight do they need to be to "lock" the girdle to the studs/nuts/caps/block ???

Then --- how do you get a girdle AND a windage tray to be happy in a baffled oil pan?
That is where I hit a road block on my stroker build --- ended up not runnig a windage tray and building it that way - then sold it without ever hearing it run! oh well.

[dartman366]

Re: Main cap girdle's....do they work??

Thank's guy's this is the type of response's and info that I was looking for and hearing it from guy's like Steve D, Dave F, and Eddie make me feel like I didn't make a wrong decision in buying one for my smallblock mopar, now I just thought of another post to start......billet main cap's ;D

[TheSilverBuick]

Re: Main cap girdle's....do they work??

Remember adding any mass to a harmonic situation will dampen vibration effectively moving the damaging vibration to a higher rpm, all assuming this theory is correct and it is vibration. Harmonic Balancers are an obvious example. Girdles are a regular thing for Big Buicks, but they like to split the block.

[dulcich]

Re: Main cap girdle's....do they work??

I don't have any doubt that a girdle helps. A lot.
-dulcich

[1FastMopar]

Re: Main cap girdle's....do they work??

Yeah, I guess it will dampen by tying the caps together, and the pan rail too. When I think of a damaging harmonic it is a vibrational disturbance of a certain sufficient amplitude to be damaging dependend upon the frequency of the vibration frequency and the resonant frequency of the material or structure.
-dulcich

See, now your getting to "scientific" for me.. lol I'm just a silly engine guy that doesn't always go along with conventional thinking..

[1FastMopar]

Re: Main cap girdle's....do they work??

well in your theory wouldnt the girdle give a new path for the harmoics to travel?

Main cap movement is more prevalent at higher RPM, the crank speed is reaching points where it "floats" in the mains and one hint of detonation will interrupt that..... The support will help control the "hit" of that detonation by letting it travel across the area instead of being focused on one main.

Keep RPMs lower and keep it safe and you wont ever have to really worry about tearing up a block.

Well, I feel that on the BB Mopar it travels down the oil pan rail and back and helps to rattle the bottom end apart.. Ever see the outside of a BB Mopar crack right where the oil pan rail meets the bottom of the block, I feel that area that cracks supports my theory...

[dulcich]

Re: Main cap girdle's....do they work??

Yeah, I guess it will dampen by tying the caps together, and the pan rail too. When I think of a damaging harmonic it is a vibrational disturbance of a certain sufficient amplitude to be damaging dependend upon the frequency of the vibration and the resonant frequency of the material or structure.
-dulcich

[Tommygun]

Re: Main cap girdle's....do they work??

well in your theory wouldnt the girdle give a new path for the harmoics to travel?

Main cap movement is more prevalent at higher RPM, the crank speed is reaching points where it "floats" in the mains and one hint of detonation will interrupt that..... The support will help control the "hit" of that detonation by letting it travel across the area instead of being focused on one main.

Keep RPMs lower and keep it safe and you wont ever have to really worry about tearing up a block.

[1FastMopar]

Re: Main cap girdle's....do they work??

I think it is very simple geometry, and all the rest is BS. XYZ axis, span of the cap in one axis, bolts and "bridge" of cap in another, and near nothing in the third until you put the girdle on it. I don't know what you mean by the harmonics but I guess is sounds good.
-dulcich

Well, I fully understand what your saying, but harmonics are very destructive and I feel that harmonics are reduced in the main cap area with the girdle tying the mains together, furthermore on the BB Mopar I feel those same destructive harmonics travel down the oil pan rail and amplify like harmonics resonating through a bell, the main girdle that I worked up a number of years ago helps to dampen all that.

I guess so much of what we do is not always cut and dry, its theories that some of us believe that advance things and over time become fact. How many times did some very smart people out in the World feel that some of the stuff that Smokey believed in was nuts, he proved those rocket scientists wrong many of times.