Moparts
Why do only Mopars experience "cap walk"???
Posted By: Ramcharger
Why do only Mopars experience "cap walk"??? - 12/13/04 04:47 PM
I have been watching the Low-Deck Super Block thread with great interest. It is an interesting proposition. The suggestions for a new and improved race block are very creative. But I do have a question. Why are big block Mopars plagued with cap walk and Chevys are not? Does the Mopar block simply lack the sufficient clamping force capabilities that the 4 bolt Chevy main caps have to prevent cap movement? Cap walk seems to be an ever-growing problem that more and more racers are experiencing. What is the actual cause of cap walk? I know that things such as detonation contribute to the result (damage), but exactly why is it happening?
Posted By: M_D
Re: Why do Mopars experience "cap walk"??? - 12/13/04 05:37 PM
My opinion is that a pair of 1/2" bolts don't have enough clamping force for the higher loads. The stock blocks also don't have any too much material in the main webbing either. The cross bolts help, but I think a splayed 4 bolt holds the cap and block together best.
Posted By: AndyF
Re: Why do Mopars experience "cap walk"??? - 12/13/04 05:47 PM
The blocks were designed back in the late 50's. No computers, no finite elemant analysis, no expectation of making 800+ hp. It is a surprise that they work as well as they do. If the block design was imported into a modern analysis program then it would quickly become clear where material needed to be added to solve the cap walk issue. As far as I know, nobody has done that.
I assume the Pro Stock block benefitted from FEA work but I've never seen what those blocks look like on the bottom end. If someone was going to cast a new block they could probably cheat a bit and just copy the Pro Stock block on the assumption that it was done correctly.
Posted By: Blown71X
Re: Why do only Mopars experience "cap walk"??? - 12/13/04 06:43 PM
Don`t assume that Chevy`s or Fords are immune from this either, I was up close and personal with a carillo crank and rodded, billet 4 bolt cap (not splayed) 14:1 355" small block that routinely sees 8000 rpm, a while back, that if you were to take a picture of the mating surfaces only, you would swear it was a BB mopar
I absolutely agree with MD and andy also that it is a combination of issues, Bolt clamp force, Block flex, etc...As Andy said..it really is amazing that they take what they do, considering the crudeness (is that a word ?) by todays standards on how they were designed.
Rick
Posted By: Anonymous
Re: Why do only Mopars experience "cap walk"??? - 12/13/04 07:11 PM
4 bolt mains don't mean anything unless they are splayed and doweled. thats the only way to keep them from moving around. the BBC merlin blocks with ductile iron caps without dowels have cap walk too. as i said before, splayed and doweled is the way to go. we routinely see merlin and dart blocks holding up to 1800-2200 HP without cap walk. don't you wish a mopar block would do that.
if it's worth doing it's worth doing right. don't skimp like MP did and have a heavy iron block that still has issues. it would be a waste of time and money in the investment and the same for the end user IMO.
Posted By: Tig
Re: Why do only Mopars experience "cap walk"??? - 12/13/04 07:46 PM
Sorry to butt in on this thread, but I was dissapointed to hear that the mega block has issues too. Would a block girdle help on this block too?. I'm almost in the process of obtaining parts for a 572ci motor and was hoping for 850+ Hp. As far as I can tell I've had no problems with my 528ci making around 730 hp on a good day, but I hear thats approaching the limit before cap walk becomes a problem.
Posted By: Anonymous
Post deleted by Defbob - 12/13/04 08:07 PM
Posted By: CRE2004
Re: Why do only Mopars experience "cap walk"??? - 12/13/04 08:17 PM
Quote:
4 bolt mains don't mean anything unless they are splayed and doweled. thats the only way to keep them from moving around. the BBC merlin blocks with ductile iron caps without dowels have cap walk too. as i said before, splayed and doweled is the way to go. we routinely see merlin and dart blocks holding up to 1800-2200 HP without cap walk. don't you wish a mopar block would do that.
if it's worth doing it's worth doing right. don't skimp like MP did and have a heavy iron block that still has issues. it would be a waste of time and money in the investment and the same for the end user IMO.
You hit the nail on the head with the 'doing it right' statement!
I agree that the splayed bolts help keep the caps from moving as do the dowels, but from what I've seen, they are only keeping the bottom of the cap from moving and transferring metal, the rest of the cap is still having to deal with the harmonics which is why it's no surprise that I feel a girdle(in conjuction with whatever main cap you choose) is the only way to fully stabilize the bottom end on a BBM. The aluminum caps seem to dampen the frequency a little better than steel and iron, and are softer giving little or no signs of transfer, but I'm not a fan of aluminum caps on multi climate street cars. JMHO..
Posted By: moper
Re: Why do only Mopars experience "cap walk"??? - 12/13/04 08:35 PM
Yeah, all makes can experience it..Many small block chevies I've seen have caps that fit loose, even the 4 bolt mains..I'm talking stock blocks here...But, the chevy design has a greater footprint on the parting lines, and I think this adds to the fastener's holding ability. A big block mopar has less area there, and it adds stability, even with the 2 bolts. I would be interested to see what some "out of the box" thinkers can come up with...Perhaps eliminating some pan bolts and adding material to the cap areas, and splaying the second set of bolts like the 6 bolt version posted in the other thread..I think 6 is overkill if the cross sections and caps are enlarged a bit. Also loose the "hollow" between the cap and block skirt, use that for more contact area between the cap and main web.
Posted By: Ramcharger
Re: Why do only Mopars experience "cap walk"??? - 12/13/04 08:58 PM
I thank all of you for confirming what I suspected. It appears to be a design issue in high horsepower applications. Doweling seems like it might solve some of the issues but is there enough material/room to install dowels in a Mopar? And how about CRE's idea of the girdle. Would it be possible to incorporate some preload against the mains when installing a girdle? I know that it wouldn't be much, but, would it be enough to make a difference?
Posted By: CRE2004
Re: Why do only Mopars experience "cap walk"??? - 12/13/04 09:13 PM
Quote:
And how about CRE's idea of the girdle. Would it be possible to incorporate some preload against the mains when installing a girdle? I know that it wouldn't be much, but, would it be enough to make a difference?
If you run a heavy girdle like what Best Machine posted, a little preload on the cap could be achieved. However, I feel that the reason for the cap walk/bounce is that the cap is trying to go oval and is flexing in a circular manner consistant with crankshaft rotation. If you can stop the begining of the movement by bracing the cap sideways against the block, it helps disipate the harmonics into the block and prevents the flexing cycle from even beginnning. The preload might help some on the 850+ hp applications, but it's the unification of the entire bottom end that's critical. Take a look here and try to envision what I'm saying...
My stud girdle page...
Posted By: RT540
Re: Why do only Mopars experience "cap walk"??? - 12/13/04 09:13 PM
Quote:
What if you take a Megablock, and add dowels to the caps and use tight fitting shoulder bolts instead of the standard cross bolts? Would this help with cap bounce?
You just described exactly what have been done to my block. It still got some cap walk itīs not much but itīs there. Why when only having 810hp ?? with 35° timing and flat tops with 13:1 and C12 fuel I shouldnīt have detonations, but........
Heres a pict. of the cross bolt.
Posted By: RT540
Re: Why do only Mopars experience "cap walk"??? - 12/13/04 09:17 PM
Quote:
Doweling seems like it might solve some of the issues but is there enough material/room to install dowels in a Mopar?
Yes, look at the att. picture, sorry for the bad quality of the pict. itīs an old one as I donīt have a cap off right know.
Posted By: Ramcharger
Re: Why do only Mopars experience "cap walk"??? - 12/13/04 09:22 PM
RT, what kind of dowels did you use and where are they available?
Posted By: Anonymous
Re: Why do only Mopars experience "cap walk"??? - 12/13/04 10:23 PM
CRE2004, i think you might be missing my point, not sure. you won't have the harmonics if the caps aren't moving. no need for the girdle in that case. i've never put a girdle on a BBC 1800HP motor and i've not seen any problems with blocks breaking or caps walking with the 4 bolt splayed and doweled billit caps. the fact is that it works.
Posted By: Anonymous
Re: Why do only Mopars experience "cap walk"??? - 12/14/04 12:01 AM
CRE, your system looks good , too me. How is different(if any) from the the one Dvorack has been offering?
Posted By: CRE2004
Re: Why do only Mopars experience "cap walk"??? - 12/14/04 05:11 AM
Quote:
CRE2004, i think you might be missing my point, not sure. you won't have the harmonics if the caps aren't moving. no need for the girdle in that case. i've never put a girdle on a BBC 1800HP motor and i've not seen any problems with blocks breaking or caps walking with the 4 bolt splayed and doweled billit caps. the fact is that it works.
I got your point, I was just thinking one thing and typing another. I agree with you on doweled, splayed, billet 4 bolt caps, no doubt. What I was thinking of is doweled two bolt Mopar main caps. You can pin down the bottom of the cap and hold it steady, but the harmonic is still present and the cap will still flex and move as it forms and egg shape and the shape changes as the crank rotates. The two bolt BBM main cap design is far from ideal, and as pointed out above, would greatly benefit from a cap with side contact to the block like a hemi cross bolt. The function of the cross bolts and the girdle are similar. I know you'll have to try one successfully before your convinced... 
Mike
Posted By: CRE2004
Re: Why do only Mopars experience "cap walk"??? - 12/14/04 05:32 AM
Quote:
CRE, your system looks good , too me. How is different(if any) from the the one Dvorack has been offering?
Dan's system (pictured below) is a four bolt main cap conversion requiring some fairly involved machining. Our girdle is a true bolt on piece that augments the two bolt cap setup and ties them into the block sides boxing in the entire lower end. The end results of both methods are similar, just different ways of getting there.
He lists his setup as withstanding 1500hp and I'm not in a position to doubt him. The most power put to one of our girdles so far is a 935hp dragster running stock 400 main caps. It broke two cranks the season before the girdle and ran all last season with no issues after the girdle installation. It's not the end all be all of mopar bottom ends, it's just our solution to a pesky problem.
Dan's 4-bolt conversion...
Our main stud girdle
Posted By: Anonymous
Re: Why do only Mopars experience "cap walk"??? - 12/14/04 05:50 AM
Hey CRE, here's a question for ya. Will having the block absorbing the harmonics using a girdle make a stock RB block last to higher HP levels before braking in the main webs? Is it the harmonics that are a major contributor in RB blocks failing in the web area?
Posted By: CRE2004
Re: Why do only Mopars experience "cap walk"??? - 12/14/04 06:17 AM
Dart68,
I haven't had the luxury of tearing down any RB block main web failures yet...(I'm sure my day is coming) but I would think that many are a combination of 30+ year old cast iron, minute cracks and casting imperfections, major block flexing from harmonics and who knows what other contributing factors. Will a girdle make an engine last longer from a durability standpoint than one without? That's yet to be determined and probably dependent on HP levels, rpm, rotating assembly weights, car weight, and a bunch of other things. Will it allow you to sustain a higher HP for a longer period of time prior to failure? I firmly believe it will.
Posted By: Anonymous
Re: Why do only Mopars experience "cap walk"??? - 12/14/04 06:18 AM
i don't mean to demean girdles. i'd enjoy hearing more about the broken cranks and what type and brand they were. as it's been said a million times, the factory blocks were just never engineered to withstand that type of HP. don't take this the wrong way because 900+ HP is nothing to sneer at if it continues to work, but do you feel it would work as well in a heavy car situation as well as it does in a light chassis like a dragster.
i think there are pro's and con's to both steel and aluminum caps. we've seen a number of guys break the stock caps with what i would consider fairly mild motors at 650 or so HP. has that motor your referring to been torn down yet to see the effectiveness at reducing walk and or bounce of the caps?
people seem to forget that better higher tensile strength studs are available to help with the obvious issues. there is also enough material to go to a larger stud which does help. i'm sure harmonics plays a huge roll in a lot of block failures. unfortunately many machine shops just don't have the ability to dowel the mains either. it truely is a worthwhile investment if your engine will be on the edge of failure without it.
i'll be doing a mild RB 511 combo for my own car this year if you want to donate a girdle for testing
, LOL. it likely won't be much over 700HP though. thats about all i'd want in a street pumpgas combo.
on another note, i applaud everyone thats trying to make improvements for the parts most have available to use.
and lastly, one of the problems that people just refuse to belive for the most part is that soft chinese forgings actually aggravate the cap bounce issue due to all the flexing that goes on. it causes a multitude of other problems as well. of course if your building a mild combo i guess it shouldn't be much of an issue.
Posted By: RT540
Re: Why do only Mopars experience "cap walk"??? - 12/14/04 06:39 AM
Quote:
RT, what kind of dowels did you use and where are they available?
I didnīt do the installation and I didnīt even own the block at the time, but it was Jari Konola here in Sweden who made both the new crossbolts and installed the dowels. Sorry for not answering you quicker but itīs 6 hours time diff. to the eastcoast for me, so I have been sleeping.
Posted By: CRE2004
Re: Why do only Mopars experience "cap walk"??? - 12/14/04 06:45 AM
Quote:
don't take this the wrong way because 900+ HP is nothing to sneer at if it continues to work, but do you feel it would work as well in a heavy car situation as well as it does in a light chassis like a dragster.
Not at all, there's a major difference in stresses implied by a heavier car, and I think that's in part why he's been able to get away with using stock caps at that HP level.
Edit: one thing that is yet to be determined; is the stud girdle easily handling the 935hp stock cap combo in a light dragster or is it at the ragged edge of its limits. I guess we'll determine that once I find a 935hp stock main cap engine in a 3800# drag car to test with.
Quote:
has that motor your referring to been torn down yet to see the effectiveness at reducing walk and or bounce of the caps?
Not yet that I'm aware of , but I'll inquire and post back with pics if I can get 'em.
Quote:
i'll be doing a mild RB 511 combo for my own car this year if you want to donate a girdle for testing , LOL. it likely won't be much over 700HP though. thats about all i'd want in a street pumpgas combo.
I think you'd be a very impartial test subject 
maybe I'll take you up on that 
Quote:
people just refuse to belive for the most part is that soft chinese forgings actually aggravate the cap bounce issue due to all the flexing that goes on. it causes a multitude of other problems as well.
They were Exxxx cranks that broke.. 
Mike
Posted By: Anonymous
Re: Why do only Mopars experience "cap walk"??? - 12/14/04 09:29 AM
Quote:
Dan's system (pictured below) is a four bolt main cap conversion requiring some fairly involved machining. ..... He lists his setup as withstanding 1500hp and I'm not in a position to doubt him.
Dan has one customer with a Blown Alcohol Tractor pulling rig that is exceeding 2500HP on one of his 4-Bolt conversions. Would not have believed it if I hadn't seen it with my own eyes. 
Posted By: RapidusMaximus
Re: Why do only Mopars experience "cap walk"??? - 12/14/04 11:41 AM
Lot's of great reading here...even if it does make my hair stand up...my 496 is a lo deck with Muscle Motors Aluminum caps, ARP stud kit, eagle crank and rods, Ross pistons, ATI Super Damper and a partial fill on the block...sees 6800 on the shift chip...based on the ET/WT ratio figure the car is making close to 800 hp...only made about 100 passes last year ...so...I can only hope I'm "controlling" my cap bounce...what do you think?
Posted By: CRE2004
Re: Why do only Mopars experience "cap walk"??? - 12/14/04 12:36 PM
Quote:
Quote:
i'll be doing a mild RB 511 combo for my own car this year if you want to donate a girdle for testing , LOL. it likely won't be much over 700HP though. thats about all i'd want in a street pumpgas combo.
Quote:
I think you'd be a very impartial test subject maybe I'll take you up on that
oh well, i guess with all the hammers and laughing guys that means no. i set myself up that for that one real well.
Once you get that 511 underway, have your people contact my people and we'll work something out .......'looking for the shady mobster emoticon but not finding it'...
Posted By: Duster499
Re: Why do only Mopars experience "cap walk"??? - 12/15/04 12:40 AM
IMO a contributing factor is the poor machining done by Crysler's production equipment. The blocks I've inspected and machined show the mounting surface for the main cap to be out of flat by .0015". This is one each cap surface, not the total condition. This would cause the main cap to contact the block only on the 'crests' of the surface reducing the compression strength by limited contact. It would also allow more motion in the cap than if there were full contact. Motion of the cap will be transferred to the main bulkhead through the cap bolts resulting in vibration that will eventually cause cracking and failure of the main bulkheads. My solution would be to machine the mounting surface and caps flat and use a girdle to eliminate or at least reduce cap motion.
Posted By: dave571
Re: Why do only Mopars experience "cap walk"??? - 12/15/04 03:57 AM
I have yet to see this "cap walk" first hand.
I'm not doubting it, or anything like that...
I'm curious...
At what horse power level does it start to become evident?
Posted By: RapidusMaximus
Re: Why do only Mopars experience "cap walk"??? - 12/15/04 11:26 AM
I didn't realize what I was looking at the first time I saw it and that was during the rebuild of a .030 over, stock crank, stock rod engine that was probably making between 500 and 600 hp...it wasn't until I had the engine back in the car that a buddy at the track ask if my main caps were walking...????
...oh well they were still bouncing when I took it apart about 500 passes later...
...after that I started making more horsepower, added studs...then aluminum caps and studs...still bouncing/walking caps...
I guess it's just something to live with until I install a girdle, cross bolt it of buy an after market block...
Posted By: Anonymous
Re: Why do only Mopars experience "cap walk"??? - 12/20/04 03:35 AM
At what Hp level does this start? Is it RPM related too or does torque play a part too?
Posted By: paul69cuda
Re: Why do only Mopars experience "cap walk"??? - 12/21/04 06:44 PM
my experiance with this is i was at the crank dyno 648 hp/595 torque with 300 shot nos in a 3400 lbs 69 tubbed cuda with a stock crank and caps. it ran great and held together for about 200 runs but it finally gave last summer. and no im had no idea about cap walk or anything like that i was told i was on the edge everytime i hit the nos but go or blow is my moto. this time im getting alluminum caps and i have the cre stud girdle. so this summer i will make more hp and tell your what i find out. if it works great if it didnt i will let you know.
Posted By: CRE2004
Re: Why do only Mopars experience "cap walk"??? - 12/23/04 05:17 PM
We just heard from our customer who's running our main stud girdle with the 935hp low deck with stock caps in a dragster. He pulled the lower end apart and stated that the bearings look as if they only had one run on them and zero signs of cap walk present. Some of Jerry's comments were that the vibration level was extremely low and the dragster was much 'smoother' to run. They turned this engine all season on one set of bearings at 8100rpm.
I'm glad we were able to help them out and it looks as though we'll be machining them a new block for next season...
Posted By: 68charger
Re: Why do only Mopars experience "cap walk"??? - 12/24/04 04:27 AM
i think if you want to prove to everybody on this board that your girdle works you need to donate one to a guy like performance only who everbody knows from the board but he would need to put it on a real motor say 1000hp or so just my two cents
Posted By: Anonymous
Re: Why do only Mopars experience "cap walk"??? - 12/24/04 02:14 PM
I'm glad we were able to help them out and it looks as though we'll be machining them a new block for next season...
Just curious, why the new block if everything looked OK on the tear down?
Posted By: smokinwoody
Re: Why do only Mopars experience "cap walk"??? - 12/24/04 03:37 PM
we ran a 448 in our Duster.. we had main bearing failure which led to a snapped rod..when I tore down the engine,cap walk was very evident.This engine was an easy rever to 7800 but was never shifted higher than 6800...our new engine is a 499 which is now making in excess of 800+hp..we have as you know your stud girdle and I have found it very smooth..of course my wife races the car so trying to pull data out of her is...you know...we only made 3 runs since the season ended clocking an amazing 9.23 shutting down at 1000' and soft launch...Becky's remarks were"It's so smooth and POWERFUL"(a woman's insight to just about everything)..she has all the confidence in the world with this new engine...on the dyno it was smooth past 7500...when we teardown next season..we will see how well a 2 bolt main and stud girdle will do on bearings.....
Posted By: OldHippie
Re: Why do only Mopars experience "cap walk"??? - 12/24/04 06:06 PM
A few years back, before buying my Mega Block, I inquired about any strength issues that the stock Ductile Iron Cross Bolted main caps might have. Muscle Motors replied that they had not had any issues at 1300+ Horsepower, but I am thinking that may have been Dyno blasts, not on track testing. So, would using either stud girdle in conjuction with the Ductile Iron mains and Cross Bolting be practicle at, say, 700 HP or so? Overkill? Tossing good money after bad? This in a 3400+ Lb. "B" body. I am a firm believer in building killer bottom ends, it tends to save $$$$ in the long run.
Posted By: Anonymous
Re: Why do only Mopars experience "cap walk"??? - 12/24/04 07:30 PM
Being new to the "Mopar world" a few years ago.. I built my first hard core r/b engine. I had heard of the block problems, As I had done a few mild builds in the past. This engine I`m speaking of was gonna make some big #`s. W/ that in mind, I set off to think of what I should do to help deal w/ this problem... I had been working on imports for some time and seen how they would tie the mains together, Also seeing the systems that were already out there for the S/B Chevys and Fords, Even though its a different design block. Not knowing anything about "old" hard core mopar guys, In the past making anything like a main girdle plate(How true this is, I dont know).. The next logical thought I had was, I GOTTA make something to tie this week block together and get the main caps and block from poping!!
So, without any "outside" help, I designed the plate system.. You know, Thats the one that EVERYONE talks about now!!!
From what I gather, nobody was really thinking about it much, until I started selling them on ebay a few years ago.. At that time I didnt pay ANY attention to the Mopar web site, I just got outside info from people who did, And they said your main girdle system is being talked about on the forums.. Next thing I know is, Everybody and there mother said, "Look at this great idea I had.. This is the ticket!! YOU NEED A MAIN GIRDLE PLATE!!
Its great that an "old" Chevy guy, Could be such a help to u guys!!
Really, I work on them ALL! I do not like putting blinders on and only working on one brand of engine.. I think by being SO closed minded, To think that there is nothing else out there but MOPAR,just hurts your ability as an engine builder.. I`m not degrading the abilitys of Mopars to run.. I have been VERY impressed w/ the ones I have built!!! Look at my little pump gasser!
Out of the box, With nothing more than a stock cranked 446, W/ no tune and a 1.48 60ft... 9.75 @ 140mph!
Let the bashing begin!!
Posted By: CRE2004
Re: Why do only Mopars experience "cap walk"??? - 12/24/04 09:21 PM
Quote:
Just curious, why the new block if everything looked OK on the tear down?
They're putting together a new B1 engine and keeping this years as a backup. The new one should turn 9000rpm.
Posted By: CRE2004
Re: Why do only Mopars experience "cap walk"??? - 12/24/04 09:24 PM
Quote:
...on the dyno it was smooth past 7500...when we teardown next season..we will see how well a 2 bolt main and stud girdle will do on bearings....
Thanks Jeff, I'm looking forward to seeing the bearings too...should look good!
Posted By: PaxtonedProCuda
Re: Why do only Mopars experience "cap walk"??? - 12/24/04 09:27 PM
I will back up his story as he was the first I had seen to offer one and yes I hate to admit it but I saw it on the Bay. I too had heard people mention they have been around for years but a phone # or websight to order one.... he was the first I had seen. I also agree that you can't stay close minded to certain things like the other manufacturers. You have to keep an eye on the competition to stay ahead of the competition. Did you really say chevy and import???? It's Christmas so I guess we will let you get away with it! Happy Holidays to you and yours, everyone!!!!!!!!!!!!!!!!!!
Posted By: 72chrgrally
Re: Why do only Mopars experience "cap walk"??? - 01/29/05 01:28 AM