I am working on a 1988 Suzuki LT500R Quadzilla that my son has beautifully restored.  I am a retired (52 years) machinist/instrument maker.  I have a home workshop that includes lathes and milling machines.

This is what I need to know:
What are the tolerances on the main bottom end crankshaft bearings?  The cases are beat out and I will have to bore the cases and insert a steel sleeve.  I will bore the sleeve to the tolerance needed to fit the bearings.

Does anyone know these tolerances? 

Thank you for your help.

The engine builder I used is Mike Steiner (msteiner@sucocoopwb.com) located in Kansas.  His website is http://fulltiltmusclecars.com/


Building the LT500's is a hobby of his, so it is not the fastest turn around, but he is very reasonable on prices.


Another option for a builder is Jerry Hall of Halls Precision Racing (themotorgeek@gmail.com).  Hall is pretty busy most of the time now, so it could take a few months for a port job.


I have a friend with a LT500 and he was happy just doing a basic port cleanup in his Zilla himself.


IMO, it is most important to fix the head squish velocity, angle, and piston to head clearance.  When this is 'fixed' the Quadzilla's don't detonate as much and cause the loose bearing pockets you are asking about.


Here is some information from MotorGeek (Jerry Hall):


Why does the LT 500 Suzuki have problems with the bearing pockets wearing out?
Our first guess was that the main bearing pockets were loose on the new engines. We started measuring the bearing pockets on new cases and found that Suzuki was setting the interference fit between the main bearing and the bearing pocket where it should have been. Our next observation was the problem seemed to appear on the “stockish” type engines that had a million miles on them or on the race engines. We began to see other problems, broken crank pins, and broken crankshafts on the ignition side at the junction of the main bearing shaft and crank web. We began to study the failures and the failures pointed to the cause of the problem. Before a part breaks, it has to flex. The flex leads to fatigue and the part will eventually crack and break in the fatigued area.


Crankshaft flexing is what wears out the bearing pockets. The majority of the flex occurs in the crank pin. Another area of flex is at the junction of the main bearing shaft and the crank web. How do we know that these areas flex? These are the two areas where the crankshaft breaks.

What causes flex?
The two major factors that contribute to the flex of any crankshaft are high rpm and the load that the connecting rod exerts on the crank pin when the engine is under full power.

The connecting rod is experiencing high tension as the piston approaches top dead center, when the engine is at high rpm and the throttle is closed,. The piston is pulling on the connecting rod with a force of thousands of pounds. As the rpm is increased this force increases exponentially. This force causes the crank pin to flex so that the distance between the crank webs DECREASE in the area opposite the crank pin.

When the engine is under power, the piston exerts force on the connecting rod and the rod transmits this force to the crank pin. The peak pressure on the piston occurs in the neighborhood of 20 to 30 degrees after top dead center. When the power level of the engine is increased, the crank flexing force increases. The force on the crank pin when the engine is under power causes the crank pin to flex so that the distance between the crank webs INCREASE in the area opposite the crank pin.

The flex in the crank pin is not visible, but it exists on a micro level. For discussion purposes the main bearings should be thought of as being part of the crank webs. Looking at the motion of the crank webs described in the above paragraphs, we can easily observe the motion of the main bearings. The interference fit between the main bearings and the bearing pockets helps resists some of the motion of the bearings, but some movement of the bearing will occur when the crank pin flex exceeds a certain level.

The friction and extreme pressure between the outside of the main bearing and the bearing pocket causes micro welding to occur between the two surfaces when they are both iron based materials. The micro welding is what causes the pits to occur on these surfaces.

How can we prevent the problems described above?
One obvious solution would be to increase the diameter of the crank pin. Increasing the crank pin diameter would require an increase in the outside diameter of the crank webs if we are to maintain a reliable design. The proper interference fit between the crank pin and the crank web must be maintained in order to prevent movement between the web and the crank pin. I have never seen a stock LT500 crank web split between the crank pin hole and the outside diameter of the crank web. I have seen the crank webs split between the crank pin holes and the outside diameter of the crank web when the correct interference fit on the crank pin is used on stroker cranks. There is not adequate strength between the crank pin holes in the web without increasing the OD of the web. Welding the crank pins to the existing webs should not be considered as an option. Welding crank pins to the webs are just band-aids for a poor design or loose crank pin holes. A large diameter crank pin is also not desirable for high-rpm two strokes due to the increased moment of inertia of the bearing cage assembly and the pre-mix type of lubrication system

Another solution would be to run two main bearings on each end of the crank. This is not an affordable solution because it would require a new crankcase and crankshaft design.

We started seeing bearing pocket failures on the 1987 race engines before the 1988 models were released. The LT 500 engine was designed for power levels in the 40 hp to 50 hp range and engine speeds of around 6500 rpm. We often spin these engines over 8000 rpm and we can easily produce power levels in excess of 80 HP. The bearings are going to move in the bearing pockets when we elevate the power and rpm. So what is the best cost based solution?

We re-sleeved the early pocket failures with steel inserts on the first race engines. They did not seem to last much longer than a new set of cases that had cast iron inserts. The steel inserts would eventually get loose and had the pitting problem like the cast iron inserts. We used brass inserts and then silicon bronze. The bronze seemed to last longer but eventually wear out. The bronze did not show any pits when they got loose like the iron bases inserts. We also tried aluminum inserts and they eventually got loose without pitting. We eventually came to the conclusion that the main bearings are going to move in the bearing pocket. What can we use as material between the bearing and the cases that will minimize the wear? We tried using plastic for an insert material and watched these engines for a few years on different customer engines. Upon teardown the bearing pockets and the outside of the main bearings did not show any ware. We have used the plastic inserts in hundreds of main bearing pockets over the last 20 years in the LT500 engines.

I do not believe that there are any “cushioning” effects on the bearings as a result of the plastic inserts. I do not believe that there is any other magical properties of the plastic inserts other than it does not ware as fast as the metal inserts.


..... and some more information from Jerry..


Measure the main bearing pockets. Many of the pockets we measure are loose enough for the outside bearing race to spin in the case but have a lip that keeps the bearing from falling out of the case. Because you have to press the bearings out of the cases is NOT an indication that the bearing pockets are tight where it counts.

There should be .0015" to .0020" interference fit at room temperature for the bearings to be tight when the cases, bearings and crankshaft are up to operating temperature. If there are pits on the bearings or bearing pocket surface the pockets need to be re-sleeved.

There is not any advantage to re-sleeving bearing pockets that are tight. All LT 500 bearing pockets will eventually get loose given enough hard run time. Flex in the crankshaft causes the bearing pockets to ware out. The bearing pockets on some of the original cases came through a little on the loose side and it did not take long for the bearings to spin or fret in the original pocket.

Pockets that have been re-sleeved will eventually get loose with enough mileage and or when the power level goes up. The material used, bronze, brass, aluminum, steel, plastic or iron does not guarantee they will never get loose again. The type of material used does make it possible and reduces the cost if they get loose the second time.

Searching around on this site, you can see some good information that has been posted.


http://www.suzukiquadracerhq.com/general-discussion-33/ways-to-check-if-you-need-crank-inserts/msg5940/#msg5940

I have read a .oo15 interference fit if you Google search it John Tice wrote a nice article on how to do it called things to do around the shop ... he is one of the most polite and respectful guys... he is getting up in his age buto still knocking out awesome work ... he did it a couple ways so read the whole thing and divide which is better for yourself