undersized timing chains

[thomas g. warner]

Very few rebuilders know how to properly fit a timing chain. Most do not
know how to tell if an UNDERSIZEd timing chain is needed. Here is why you
need to measure. Most of us did not buy our GMCs new so we have no way of
knowing whether the engines have been rebuilt or not. Sometimes when
rebuilding the shop will line bore the main bearings, adn redo the crank.
If they have, than an undersized chain is probably needed and Cloyes true
roller chains are furnished in .005", .010" and .015" undersized.

The measurements are:

front main bearing housing bore and the front of the cam bearings is 2.424".
The dimension is 2.363" without the cam bearing installed. When the
camshaft and crankshaft are installed, the stock timing/crankshaft gear
center to center dimension is 5.044"

>In a message dated 10/6/99 10:09:05 PM Central Daylight Time, MTrovao
>writes:
>
>> Its on the winter project list along with the Cloys timing chain to be
>> installed.
>>
>Manny
>
>Have you put the pump on yet? If not please give me any numbers
>that appear on the pump. I am going to chase this thing for a while.
>Also did you have to measure for the timing chain? Thanks.
>
>Take Care
>Arch
>
>

 

[thomas g. warner]

?Arch this is only the beginning. Anyone can build and engine and heads.
What we are looking for is an engine that is RELIABLE and lasts a long time.
That means we have to do a lot of extra work and analysis.

>In a message dated 10/7/99 9:57:34 AM Central Daylight Time, warner
>writes:
>
>> front main bearing housing bore and the front of the cam bearings is 2.424".
>> The dimension is 2.363" without the cam bearing installed. When the
>> camshaft and crankshaft are installed, the stock timing/crankshaft gear
>> center to center dimension is 5.044"
>>
>Tom
>
>WOW what can I say. I sure never knew this stuff.
>
>Take Care
>Arch
>
>

 

[thomas g. warner]

I dont have a problem in making an informed choice Rick. But I do have
reservations with several of your remarks.
1."It is my experience that ALL mechanics, you, me, and Mondello for
instance, are pretty darned opinionated." Sure we are and sometimes there
are many ways to skin a cat. For example there are a 100 different cam
grinds that will work with the GMC motorhome. You might pick one cam grinder
and i like another. Thats an informed choice. But lets not confuse having
the know how to make an informed decision with just acting on hear say,
because someone else that knows nothing about cams heard from several others
that cam 123 is hot. I have a problem with that.

We make tradeoffs every day. We do it every day because of a money budget
or for some other personal reason. Its when we get an engine rebuilt by
someone else and than get poor performance and an engine that goes south in
a few miles that i get a little upset. it did not have to happen. Follow
the Mondello technical manual to rebuild your 455 and it will put out lots
of horse power and torque and last a long time.

>
>> Sometimes when
>> rebuilding the shop will line bore the main bearings, adn redo the crank.
>> If they have, than an undersized chain is probably needed
>
>Tom,
> Thanks for the Heads Up. Must admit I hadn't considered this factor, as I
>didn't think align boring of main bearings was that common a practice on
>American iron. Thanks especially for the specs, it's something to check.
> As the same caveat applies to any V8 with a timing chain, I assume that
>most major manufacturers make undersize chains??? You're probably right,
>most rebuilders wouldn't have a clue. I also agree that anyone contemplating
>a rebuild/overhaul should buy a copy of Mondello's book and keep it handy
>along with the shop manual.
> It is my experience that ALL mechanics, you, me, and Mondello for
>instance, are pretty darned opinionated. Everyone must decide what works for
>them and their budget/expectations, but anyone with the experience of
>Mondello is worth listening to. That is to say, you may decide to do it
>differently than Mondello, but you'd better not ignore him. He knows where
>the pitfalls lie, and has apparently found good ways to avoid most of them.
> Thanks again.
>
>Rick Staples
>'75 Eleganza
>Louisville, CO
>
>