[xk-engine] Pulley/Balancer differences between 3.4, 3.8 and 4.2 models

We are completing the assembly of a 3.8L into a 120 and have
a balancer that was installed on this motor by the
machinist- its supposed to be off a GM vehicle, something
like a 426 Buick or something Not-Quite-Jaguar. This unit is
about 1 inch thicker/wider (standing out from the motor)
then the stock balancer. Being as though it has already been
installed and built to this unit, I am trying to find a
pulley for it along with one for the water pump that will
fit, or something that we can adapt. Also, we are using a
pump from what I believe was from a 150 because the hose
needs to face about the correct direction for the later type
radiator which we have also installed.

I understand that the offsets of the 4.2L and possible late
3.8L might be of more use to us because the balancer off the
later motors were much thicker then the early units. Does
anyone know the differences in the various 3.8/4.2L pulleys
or any other information that might help?

Also, I would like to mention I am relatively new to this
site- finally joined today for the forums and really like
what I see- great participation and a very friendly group…
Thank You in advance for your help.

-BMC.–
Brian Mc Cullough
Forest Lake, MN, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

//please trim quoted text to context only

In reply to a message from BrianMcC sent Fri 16 Mar 2007:

Hello Brian,

Welcome to the list. The 3.8 balancer is around 9’’ in diameter and
1 inch thick. There were two different 5 inch crank pulleys, a
double groove wide belt and a single V belt. There were no factory
crank pulleys for two belts, just a bolt on A/C pulley. The water
pump pulleys are around 5.25’’. The 4.2 balancer is 7’’ in diameter
and 1.5’’ thick. The bonded rubber area is wider. When the 4.2 came
out, Jaguar switched to negative ground and an alternator, and
needed to boost the pulley ratio. The 4.2 balancer has a built in
pulley to power the alternator. You need to move the
alternator/generator mount back to use this pulley. An S3 XJ6
balancer can have three stacked additional pulleys, the first is a
6.25’’ pulley which is very close to the alignment of the 3.8 damper
and crank pulley. If you are running an alternator, you are much
better off using the built in pulley to get closer to the ideal 3:1
ratio. The original water pump pulley ratio was low because the
first versions of the water pump had cavitation problems. They
increased the impeller size and reduced the water pump pulley
several times over the life of the 4.2 because of cooling
problems. If you are not going racing and using a 500 rpm idle,
you are better off using the 4.2 damper and pulleys and boosting
the speed a bit.

Paul–
The original message included these comments:

We are completing the assembly of a 3.8L into a 120 and have
a balancer that was installed on this motor by the
machinist- its supposed to be off a GM vehicle, something
like a 426 Buick or something Not-Quite-Jaguar. This unit is
about 1 inch thicker/wider (standing out from the motor)
then the stock balancer. Being as though it has already been
installed and built to this unit, I am trying to find a
pulley for it along with one for the water pump that will
fit, or something that we can adapt. Also, we are using a
pump from what I believe was from a 150 because the hose
needs to face about the correct direction for the later type


PS
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php

//please trim quoted text to context only

Hey Paul.

I don’t fully understand all the pulley differences.

I have a 3.8 that does not charge well at idle after the generator was done. But up the RPM by 300 and it charges great.

I don’t know what has happened over the past 60 years with this car. It has the double groove belt.

my question is, will the double grove pulleys from the 3.8 and 4.2 interchange? or are offsets different.

If they will interchange, what are the pulley sizes for the crank and Water pump. I would like to measure mine and see what I have, then if I can get a slightly larger pulley, do that so I can spin the generator faster. Generator pulley only comes in one size from what I can see.

Also, if the water pump can have a slightly smaller pulley, I would like to do that for better cooling.

My crank pulley is about 131 mm diameter X 35mm deep, the water pump is about 144mm in diameter X 47mm deep and the generator is about 80mm in diameter X 31mm deep.