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Mounting transmission onto engine from different manufacturer that was never
meant to be mated together possesses a major problem and that's where the
problem lies for specialized purpose builds. Mainstream manufactures normally overcome this problem by casting different case casting to mate the 2 parts together and are more OE specialized configurations. Sometimes configuration transmissions are build with bell housing as bolt on to the main transmission casing. This option is more flexible as only the small "adapter" part or the bell housing as normally called is changed thus allowing it to be mounted to different engine. This does have another dependency that needs to be overcome but not as critical. For automatic transmissions there are plenty of ready made parts that will combine flex plate and torque converter to be mounted onto it and fit on the input shaft of the transmission. In manual transmission sometimes custom flywheel needs to be made but that is a very rare case. For a custom builds the above options are most of the time are not viable options. In a very rare occasions transmission will bolt onto the engine with limited number of fasteners but the link of either torque converter or flywheel/pressure plate/friction plate would need to be adapter from various manufacturers or models. However normal process of mating those 2 parts will require an adapter plate. The plate will have mounting bolt holes to fasten it to the engine and it will also have holes for bolts to fasten transmission onto the adapter and in certain condition will have bolts pressed fit where they will protrude through and nuts are used on transmission side. Secondly an adapter is required for either torque converter or the adapter is made to be a custom flywheel where a fly wheel is sandwiched between crank shaft if starter motor is mounted on the engine block. In other cases where starter is mounted on the transmission, flex plate is not used but a starter ring gear is mounted on the custom flywheel. In our situation with General Motors LS block and Audi manual transmission we need to have the ladder, adapter plate between engine and transmission and a custom flywheel sandwiching flex plate to the crank shaft to provide cranking for starting the engine. The adapter plate has holes to allow mounting of different transaxles models. The flywheel normally made out of 4041 steel is made of aluminum in this case which has replaceable friction ring bolted onto it. This configuration allows for less expensive maintenance option if need comes to have clutch serviced as only the friction ring would need to be replaced rather then the custom fly wheel that is fraction of the cost not to mention that the aluminum flywheel is lighter and will require less force to have it spanned around. There are number of ready made adapter kits by various manufacturers that are making those adapters on per order basis as kit on per need and specific basis. However they can be rather on expensive side ($2500 - $3000 USD) as they are made to order. Trying to keep costs of the project down as much as possible we have opted to investigate of having it made our selves and see if it would be cost effective. To start with we needed to have mechanical flange drawings both of the engine and transmission. Transmission was rather easy to obtain and the bolt pattern had enough bolt holes for various transaxle models. In our case G86.10 and G87.20 which are 5 and 6 speed respectfully that can be found in various Volkswagen and Porsche vehicles. The harder part came looking for engine flange as we wanted to utilize the 2 bolt holes in oil pan of the gen 3 and gen 4 LS engines. The upper holes are standard pattern that had been used since the Chevy small blocks where made. Closest thing that we had found was a mechanical drawings of SBC block and a bell housing of transmission used as combination with the engine which has the 2 lower bolts. Making the adapter Having all the dimensions and pictures of the transmission flanges we had them imported to a CAD programmed and scaled up to appropriate dimensions. This first step allowed of drawing the outer most dimension for the LS block which is larger then the Audi transaxle. Next came positioning the SBC bolt holes. Having them placed and measured it was discovered that ratio in scaling came around of 0.01" tolerance. Not exactly perfect but close enough to assume location of the 2 lower oil pan bolts. As they are not used for alignment they can be bit larger then actual bolt diameter and the bolt head will actually be what is holding the adapter. With that completed next came the Audi transmission bolt holes. Having Audi drawing centered and aligned to centered of the SBC drawing, Audi bolt holes where drawned and aligned. probably could skip on some of them however in order to make it compatible with other models of transmission we had opted out to leave them in. At this point we had a piece of shaped block of metal with bunch of random holes in it. To make it usable it needed clearance for LS flex plate, starter and opening for Audi flywheel adapter. As the flex plate is larger then flywheel, the adapter has to be of significant thickness and allow it to clear the flex plate but also have enough mass to bolt transmission to it hence it needs to be around 50mm thick and is same thickness as other manufacturers. This thickness is needed to have material for transmission bolts to go into and secondly to have enough of overlapping material for the Audi flange to overlap on top of the Chevy flange. With the flex plate sticking out 27mm from flange surface, it was needed to add additional 3mm of clearance. Again referencing LS drawing, inner flex plate clearance was traced which in turn was used as way to packet the adapter to produce interference spacing between the flex plate and adapter. last part of the LS components is starter nose clearance. Luckily LS starter is very small compared to the older SBC starters which only stick out 43mm from the surface and additionally it aligns with starter packet for Audi though not of an issue as the adapter is 50mm and would never protrude into the surface. Last part is to open up center of the adapter to clear adapter for the fly wheel. Switching back into Audi drawing, a simple circle was drawn as reference to packet remaining part of adapter center. Alignment dowel packets where added to finalize the drawing. Flywheel Making flywheel offered different set of problems but it relied on the adapter plate. What was required from the Audi side was distance from surface of throw out bearing or from the clutch fork to surface of the flange surface. On the engine side, we needed to have the 50mm of adapter subtracted from surface of flex plate to surface of the adapter. More to come, part is still being worked on. come often come soon |
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