Camshaft Rebuilding or not.

Camshaft Rebuilding or not.

Post by Denis Marie » Sun, 01 Dec 2002 07:45:40


I wonder if a diesel 1GM camshaft can be refurbished or not.
Some machine shop are equipped to machine the cam shaft and fit an undersize
bearing.  The tolerances I was informed that  .010" can be machined down.
In certain cases 020" was removed and new undersize bearing fitted (if
available).
They tell me that in other case a proper automatic welding machine is use to
build up the camshaft and then turned with a camshaft machine to fit the
proper bearing.
In the sixties that welding procedure was used with negative results.
I wonder if the technique has improved since and can this last .  Maybe some
one has had some experience with refurbishing a cam shaft.
 
 
 

Camshaft Rebuilding or not.

Post by Frederick Owe » Sun, 01 Dec 2002 10:02:09

Generally what they do is re machine the bearing surfaces in the block and
put in thicker bearings to compensate for the removed material if memory
serves me right this is called line boring.
Generally the lobes will be worn down as well as the bearing surfaces,so,
for the time and money involved why not just get a new camshaft if one is
available? I would not think any welding done on a bearing surface would
have too much longevity.
When I worked at Mack Trucks new camshafts for the two valve per cylinder
head engines were only about $200.00 US  and the bearings were another
$20.00 of course that was in 1989.

Quote:
> I wonder if a diesel 1GM camshaft can be refurbished or not.
> Some machine shop are equipped to machine the cam shaft and fit an
undersize
> bearing.  The tolerances I was informed that  .010" can be machined down.
> In certain cases 020" was removed and new undersize bearing fitted (if
> available).
> They tell me that in other case a proper automatic welding machine is use
to
> build up the camshaft and then turned with a camshaft machine to fit the
> proper bearing.
> In the sixties that welding procedure was used with negative results.
> I wonder if the technique has improved since and can this last .  Maybe
some
> one has had some experience with refurbishing a cam shaft.


 
 
 

Camshaft Rebuilding or not.

Post by LeGrandeRaou » Sun, 01 Dec 2002 11:03:12


Quote:

> Generally what they do is re machine the bearing surfaces in the block and
> put in thicker bearings to compensate for the removed material if memory
> serves me right this is called line boring.

Line boring can achieve this job.  Line boring is used to make sure all
the bearing bearing surfaces are 'in line'  This can be done with main
bearings, cam bearings or, for that matter, any number of bearings
which need to be straight and true. Sometimes the cam bearings
themselves need to be bored to size as well as the surfaces on the
block or head.  Sometimes (most of the time?) the cam bearing come
ready sized for the cam and just need to be pressed and pinned into the
block.

Quote:
> Generally the lobes will be worn down as well as the bearing surfaces,so,
> for the time and money involved why not just get a new camshaft if one is
> available? I would not think any welding done on a bearing surface would
> have too much longevity.

This is frequently done in the hot-rod automotive field. For tuning and
to maintain a moderate price, the lobes are welded and reground to a
different specification for a modified motor.  "Fresh-ground' new cams
are available in different specification from stock also but at a
higher price. Also, some hot-rodders change the type of lifter from
hydralic to solid or roller for performance reasons.  A performance
gasoline motor is not expected to last a long time though. Something
like a 500 HP 350 Chevy is easy to build but might only last 50,000
miles in a car or truck.

That said, welded referbished cams are available for heavy-duty
diesels.  Personally, I'd pay the extra to get a new cam and replace
the bearings in the block with appropriate sized bearings.

Jeff