From the vast quantity of parts that are still available for the Lotus twin cam engine, the pressed steel wet sump item has become a scarce and much sought after item.
The early twin cam engine sumps (Commonly known as 4 bolt) were fitted with a rope type rear crankshaft seal, the rope seal was inadequate as an oil seal, and no matter how carefully the installation was done, they were oil leakers.
The image above shows the front and rear seal of the early 4 bolt sump, the rear seal consisted of a rope seal, which is really old style automotive technology.
Another major drawback with the early 1500 twin cam engine was that the flywheel was secured to the crankshaft with only four bolts, hence the 4 bolt name given to the early rope seal sumps, a four bolt arrangement is not satisfactory for a high performance engine.
The later series of lotus twin cam engines were fitted with a six bolt flywheel to crankshaft arrangement, (Cosworth manufactured a 12 bolt crank/flywheel fixture) the rear crank shaft seal was also improved and consisted of a modern flexible lip seal type retained in a die cast alloy housing bolted to the rear of the cast iron block.
As time passed, the early engines that were fitted with 4 bolt crankshafts were converted to the later 6 bolt crankshafts which made the old four bolt sump obsolete because it would no longer fit the later 6 bolt crank seal arrangement. But back in those days, new 6 bolt sumps were readily available.
But that is no longer the case.
Today, there are firms who produce after market cast aluminium sumps for the 1500-1600 blocks which look great, but are very easily fractured or broken if the car bottoms out on something hard, and they are not cheap, and could be more than some owners could afford, and the fitment of a gated sump baffle fabricated from sheet metal may be difficult to secure without doing quite a bit of expensive interior work on the alloy sump.
Many Twin Cam Owners May Not Be Aware That There Is A Solution To The Twin Cam 6 Bolt Sump Shortage.
Recently at Croucher Engineering (elantrikbits.com) we have converted older style 4 bolt sumps over to 6 bolt sump rear crankshaft seal, and we are pleased to say that this can be accomplished with careful and precise custom sheet metal work.
The sump re-work means that the old 4 bolt rope seal metal sleeve and surrounding sheet metal is removed, and a new custom made rear fabrication which is designed to mate with the 6 bolt lip seal arrangement can be successfully grafted to the old 4 bolt sump sheet metal.
This new 4 bolt to 6 bolt sump conversion should have the effect of increasing the supply of original sheet metal 6 bolt sumps available for the Twin Cam engine, which in the past, may have hampered an engine build project due to the scarcity of the later 6 bolt sumps.
Six bolt twin cam sumps are now quite difficult to find, people who have them are reluctant to part with them, and the high prices reflect the scarcity, even good secondhand items now sell between $500 and $600, four bolt sumps on the other hand are priced quite low, but as word spreads about the sump conversion, no doubt 4 bolt sumps will become more valuable and sought after.
But the would be builder should be aware that the sheet metal fabricating work could be out of the realm of the weekend enthusiast, several special jigs, tooling and fixtures are required to make sure that everything fits as required with an absolute minimum of sheet metal distortion, but with the correct tools, jigs, welding and sheet metal forming skills, the conversion can indeed be successful, but the replication of the rear 6 bolt seal section of the sump is more complex than it first appears.
The most important jig required is a bare engine block so that the sump can be bolted to the gasket face of the block during the conversion, that is the only way that a true and accurate conversion can be achieved.
No doubt, there could be a large number of older style 4 bolt sumps kicking around various workshops which can now be converted to 6 bolt, and if you had a 4 bolt sump and you have disposed of it that is indeed unfortunate, because you have inadvertently thrown a sizable amount of money down the drain, but you weren’t to know that were you?
We are currently compiling an ebook about how to undertake the fabrication of the sump conversion, we hope to have the book available in the near future for download.
We have also undertaken the conversion of sumps to order for Australian as well as overseas twin cam owners.
Most owners also elect to include the installation of the gated sump baffle which will eliminate any oil surge your twink engine may be currently suffering, a gated baffle is a must if you intend to compete in certain classes of historic events where dry sumps are banned.
To date, we have completed conversions for Australian and international customers – 4 bolt to 6 bolt conversion which included the installation of our well known gated baffle into the sump, the international order was commissioned by a historic competitor in Europe, and that in itself indicates perhaps just how scarce twin cam sumps have become across the globe.
Would you like to learn about the tricks and hidden traps about building a sump conversion your self?
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