[Bermuda Blue]

In a recent issue of High Performance Pontiac magazine i read and artile about the 1979 trans am which state that the pontiac 400 engine as equiped with "... two bolt main caps located with special spring pin dowels"

this sounds rediculous to my. why on earth would you want your dowels to "spring" at all. it is imperative that the caps be retained as tightly as possible.

can anyone comment on these "spring pin dowels"?

i am inclined to believe that this is another case of idiots spewing garbage on the pages of a national publication. i have read the term "big block pontiac" on the pages of the national publications and they have no credibilty with me. it is amusing though.

[Bermuda Blue]

In a recent issue of High Performance Pontiac magazine i read and artile about the 1979 trans am which state that the pontiac 400 engine as equiped with "... two bolt main caps located with special spring pin dowels"

this sounds rediculous to my. why on earth would you want your dowels to "spring" at all. it is imperative that the caps be retained as tightly as possible.

can anyone comment on these "spring pin dowels"?

i am inclined to believe that this is another case of idiots spewing garbage on the pages of a national publication. i have read the term "big block pontiac" on the pages of the national publications and they have no credibilty with me. it is amusing though.

[Rocky Rotella]

While I haven't seen the article you refer to, the idea behind what was said is correct. Beginning in the mid 70's, Pontiac begun reducing mass from the blocks to reduce overall weight. The main saddles got thinner. About the same time, Pontiac began using sprung roll pins for main cap locating dowels. It is believed that the roll pins were used to reduce the tension placed in the thinner main saddle area. It appears that the W72 400's from 77-79 were those that received them. I'll contact John Witzke who has pictures of them.

Not doubting what you say the article says. The way it is worded is incorrect but what they are trying to say is true. Whether or not the author knew what he was explaining is another thing!

[larry davis]

The factory '77 cast block in my 78 TA (Y88) had the normal steel dowel pins. No roll pins at all?



SECOND AMENDMENT: AMERICA'S ORIGINAL HOMELAND SECURITY!

[firechicken]

I saw that article and assumed that they meant roll pins as opposed to spring pins. I'm not so sure how special that would be but the '77 400 in my T/A also has solid steel pins.

[Tom Vaught]

My 78 Trans Am engine had solid dowel pins.

Tom V.

[John Witzke]

Bermuda Blue, thanks for your kind words about me. Please let this idiot teach you a little something about the W72 400-cid engines. And no I do not spew bad information or as you say garbage in publications. I have probably researched and collected more factory information on the W72 engine than you will have time to try to learn in your lifetime. I am one of the leading authorities regarding factual information on the 1977-79 W72 engines and I have never misled anyone or intentionally released any untrue information about these engines. In the past too much bad information surrounded the W72 and through my detailed research I have been able to uncover many once unknown and have corrected all misstated facts that have been carelessly quoted from one publication to another and one book to another and so on. There have been so many misquoted facts surrounding the W72 engine on all websites they are too numerous to mention.

According to my “Factory Engineering Engine Booklet” that was once belonged to known Pontiac Engineer, I can share with you and the others who have commented on this subject that 1977 W72 400-cid engines codes Y6 and WA produced prior to 9/28/76 or engine number 90,568 have solid main cap dowel pins. Those 1977 W72 engines produced after that date and engine number have split sprung roll pin dowel. All base 1977-78 L78 400-cids used solid dowel pins. So in less the others who have commented about their engines have W72 engines that were never rebuilt and who were the first to rebuild them it is quite possible the pins may have been replaced with solid dowels. GM discontinued the sprung roll pins in 1987. No they are not special. The word “special” was added by the Editor. Rocky has explained very well on why they were used. In fact a very well know Pontiac engine builder who has been in the business for about 40 years knew about these sprung roll dowel pins and why the factory used them on the W72 engine. I can share with you that I have talked to people with 1978 real W72 engines prior to first rebuild that have had both solid and sprung dowel pins on the main bearing caps. Did the engine plant run short on the sprung dowel pins for some of the 1978 engines? This is unknown and may be never known without examining every 1978 W72 engine.

I understand that information in publications can be misquoted at no intentional fault of whomever, but those who have no apparent expertise on the subject they are quoting from should refrain from calling others idiots.

John Witzke
Member Society of Automotive Historians
POCI Tech Advisor
1977-79 W72 Performance Package Historian.

[This message was edited by John Witzke on February 22, 2004 at 08:56 PM.]

[Bermuda Blue]

my apologies mr. witzke. although not directed at you specifically, i should have refrained from such harsh language when questioning the use of roll pins for main cap retention.

although i am obviously not well educated in intricacies of the w72 engine, i can say that the use of roll pins for main cap retention is a bad idea and therefore it prompted my reaction to the article. It is almost comical to think of using them in a high performance application. it is highly unlikely that a roll pin could provide the same locating ability as a solid dowel and cap walk is a likely result. A correctly installed dowel will put minimal stress on the main web area (even the later thin castings where material was remmoved for weight savings). it would be interesting to find any documentation as to why pontiac went with roll pins. perhaps pontiac came to the conclusion that the cap itself was the weak link and the roll pin, although weaker that a solid dowel, was sufficient. another possibly is the fact that it would be easier to achieve the correct interface (albiet a weaker one) with a roll pin.

send me an email and give me your phone #, or i'll give you mine, and i'll apologize to you personally.

[John Witzke]

The reason for the use of the spring roll pin dowel used on the W72 engines can be debated forever. The main bearing cap bolts will hold the caps secure. The sprung roll pin dowels were used for the outer locater dowel pins. One thing we need to understand is Pontiac engineers didn't do certian things unless there was a reason for it. The best explaination I have for the use - According to some knowledgeable sources and one source from Pontiac, "the use of these spring pin dowels actually helped induce less stress into the main bearing webs of these weaker blocks during the higher RPM operating limits of the T/A 6.6 engines". These same sources say, while the spring pin dowels work well for street performance applications, these pins should not be used on racing engines.

John Witzke
Member Society of Automotive Historians
POCI Tech Advisor
1977-79 W72 Performance Package Historian.

[This message was edited by John Witzke on February 23, 2004 at 07:48 AM.]

[This message was edited by John Witzke on February 23, 2004 at 08:03 AM.]

[fiedlerh]

The roll pins will "give" a little under high stress/rpm situations where the cap may move around a bit. When I say "move around" I mean a few 1/10,000 of an inch due to block flex, bolt flex, and main cap flex. The thinner the casting the more movement you will have. A solid pin is made out of tool steel won't give, so you will tend to crack the main cap through the dowel pin hole. Since a roll pin acts as a spring, it will help locate the cap, but give a little when pushed around. This makes sense with a thinner casting in the web area. Them Pontiac engineers were smart.

http://fiedlerh.home.att.net/

[Bermuda Blue]

[QUOTE]Originally posted by John Witzke:
The main bearing cap bolts will hold the caps secure.

John Witzke
Member Society of Automotive Historians
POCI Tech Advisor
1977-79 W72 Performance Package Historian.


Mr. Witzke:

I can not dispute your unsurpased knowedge of the W72 engine. However, you do not understand the function of the main cap bolts and dowel pins (or roll pins as you have pointed out) and should refrain from comments like the one above. I suggest you do some research on main cap retetion methods. There are 2 basic methods used. Pontiac used the less popular method. Cap retention is a interesting subject, one which is especially critical to the life of a pontiac engine.

[TTS]

I assume these pins where spring steel, hollow? or where they split? The full circumference hollow pins are used alot still today, esp. in imports. I don't see a problem with them.

[John Witzke]

Bermuda Blue,

Let me see if I understand you correctly. You made the statement that I do not understand what I am talking about and I should refrain from commenting on what I do not understand. So, you are telling me that I am wrong for stating that the main cap bolts hold the main caps secure and the dowel pins which are the outer locater pins hold the cap in place and help prevent cap movement during higher rpm stress is not correct right? Or the use of the sprung roll (dowel) pins on the W72 engines helped reduce stress on the caps and block webs on the weaker blocks produced during the mid-70’s by allowing a very small fraction of give. I am wrong with this analysis too, correct? Or the fact that Pontiac used a traditional harmonic balancer on the W72 engines to help reduce crankshaft vibrations due to W72’s ability to rev higher than the base L78 400-cid engine. While I do not claim to be an engineer and it is pretty obvious neither are you.

Please explain to me where I am wrong with my analysis of main bearing cap science. Also please explain the "two basic methods" of main cap retention and why Pontiac engineers used the less popular method and what they could have done different. I will pass along your recommendations to some of the former Pontiac engineers I have contact with.

John Witzke
Member Society of Automotive Historians
POCI Tech Advisor
1977-79 W72 Performance Package Historian.

[Bermuda Blue]

Mr. Witzke:

As a matter of fact i am an engineer and have a number of documents to prove it.

Perhaps the problem here is based on poor definitions, not anyone’s lack of education or bad intentions. If ideas were more concisely expressed or defined in common terms, misunderstandings could be avoided.

No time to get into the mechanics of crankshaft dynamics and cap retention. But here are some basics. The other method of main cap retention is the use of main cap registers. As a matter of fact i think one of the new pontiac aftermarket blocks employs this cap retention method. Register retention ensures that the main cap will not "walk" (i.e. side-to-side or east-west movement). The main cap bolts can only secure the cap vertically (i.e. down or south). They provide very little support horizontally (as your statement implies). Imagine if you bolted down you main caps with little ball bearings between the block and the cap (also assume the bearings would not distort or embed in the block or cap material). The cap's vertical resistance to movement would be high and is a function of the bolts clamping ability because that is the way the bolts are oriented. However, you could probably move the cap horizontally a thou or two by kicking it with you boot. A one thou movement in the cap would be the death of a high performance engine. Don’t tell me friction between the cap and block will stop east-west movement. Even with the high clamping force, the coefficient of friction between the cap and block is no match for the forces exerted by the crankshaft. This is an extreme example but the forces on the main caps in a high power, high RPM engine are extreme too. And the crankshaft doesn’t simple push down. The force vectors imposed on the cap by the crank make cap wants to go east and west as well as south (depending on rod angles). Actually I think the cap wants to go one way more than the other but if forget which. The dowels, roll pins or registers provide the critical east-west resistance to movement the bolts can not provide.

Regular 4-bolt main caps only restrict east-west movement by increasing the friction between the block and cap. This helps but, again, the crank will win under high performance applications. The use of splayed 4-bolt mains is a decent way to restrict east-west movement. The splayed outer bolts, since they are not oriented north-south, can provide necessary resistance to east-west movement.

Every high RPM, high power pontiac engine i have disassembled (and a few low performance engines) has exhibited signs of cap walk to different degrees. Every serious pontiac engine builder has seen elongated dowel pins holes in the main caps and has had to install oversize dowels. Extreme cases where cap walk was severe enough to actually crack the ends of the cap are not uncommon. Many people think the advantage of steel main caps is that they are stronger where the crank rides. That is true, but the real advantage is the fact that the steel caps are less likely to crack at the dowel pin hole and this results in more secure cap retention. Actually, the use of dowel pin cap retention in conjunction with a steel main cap may have advantages over the register retention method

Dowels pins (or roll pins) in conjunction with a two bolt cast iron main bearing cap is fine for low performance applications (i.e. <250 HP & <5000 RPM). But i am partial to high performance engines and the engineering which makes them possible. I think Pontiac engineers designed the ideal street engine...low cost, torquey and reliable [under average street driving conditions). Its only when the design is taken to its limits do any inadequacies show [like poor oiling and broken lifter bosses). The fact that an engine designed for passenger service can produce the high power levels we have seen is a testament to the Pontiac engineers. So please give your acquaintances who were involved with the design of the Pontiac V8 my regards.

[Tom Vaught]

I had a base L-78 400 engine in 1978 so the solid
dowels matches what I had.

Tom V.

[John Witzke]

Bermuda Blue,

As a “Professional Engineer” I am very surprised you asked the question in the first place. It sounds as if you should have worked for Pontiac with as much as you know. As a respected individual in the Trans Am community I do to not start topics with a hostile intention by calling someone an "idiot". As an educated professional person myself, I realize people can respectfully disagree on a topic, but name calling and accusing someone of intentionally spewing bad information or as you call it “garbage” in a national publication is unacceptable especially for a professional person as yourself. To say your opening remarks wasn't directed towards me is hard to believe especially when my name is used in the article. The fact remains at the time the engine was engineered, Pontiac saw fit to use this part regardless of how much speculation is raised some 27 years later. This topic is getting old time to move on.

John Witzke
Member Society of Automotive Historians
POCI Tech Advisor
1977-79 W72 Performance Package Historian.

[Half-Inch Stud]

rollpin used in the main cap area was to improve MFG economics.

Solid dowel pins needed press-fit and slipfit machining quality...20 places.

The rollpin is a good idea for the cylinder head-block. I recall discussing the rollpin for the head with P. Spotts about 7years ago.

The integrated thermal expansion of a hot head to a warm block can be splits. An aluminum head grows even moreso from CTE difference.

HIS

[74Grandville]

I plan on building a high performance 74 455. Should I install role pins instead of the standard solid ones since I have a mid 70's block? Considering Pontiac installed these on their high performance w72 motor. Is this the better way to go? I would hate for my caps to crack using solid pins because they won't have the spring action of the role/spring ping.

[Skip Fix]

My 180 HP 78 motor has solid dowels. The auto tranny X7 I have in storage is unknown I haven't pulled the pan, but getting me curious enough to.

[PAUL K]

I've rebuilt 3 400 220 HP engine from 78 & 79 T/As. All 3 appeared to be never before taken apart and all 3 used solid pins .

Go fast !!! See GOD !!!