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I put lightweight Crower rods in my engine. The OEM rods are extremely heavy, and the engine really revs much easier. Most importantly, the reduction in reciprocating mass will reduce a huge amount of stress for improved longevity

Regards, Lee

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OK so now there are no moving parts left...Definitely pleased I pulled it apart to check. All pretty easy apart from the oil pick up pipe requiring some extra effort to pop out

The crank main bearing surfaces don't look too bad (Im guessing), I'll replace with new of course but its a good indication that crank might be OK and not need grinding?





Next steps I guess are cleaning and measuring.

I like the idea of lightened rods, especially if it prolongs the duration between me doing this all over again. Roughly how much for a set? From looking at their catalogue I suspect quite a chunk.

Im thinking this thread is probably better off in the restoration section?



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  • 1 month later...

Some progress with inspection and cleaning...

Decided to measure the parts as accurately as I can which involved acquiring some tools, namely a range of 0.001mm accuracy micrometers and a dial bore gauge. Some results from the measurements are published here.

I've also included some references which I have found very helpful. Im finding the process of learning very enjoyable, never knew pistons were meant to be barrel shaped and oval not cylinders, that a crank needs to be ground in a particular direction wrt to normal shaft rotation


The main bearings are all within tolerance with #1,#2,#4,#5 having a pleasantly tiny out-of-round [OOR] measurement. The centre main has a 0.013mm OOR measurement and from [1] this would suggest the crank is slightly bent. However, [2] suggests a maximum OOR of 0.01mm for a good quality rebuild so it is likely that the distortion is low.

The crank pins are quite a different story, I've posted a question about this in the Tech section which shows the excessive wear on the bearing surface. It is clear from the measurements that #1 and #4 have high degree of OOR and are less than the specified minimum dimension in the vertical direction. It is quite interesting to look at the shape of the extracted big end bearings, below is #1 and #2


So the conclusion so far on the crank is that the crank pins need to be ground down (see section in [7] for how best to do this) to the next undersize and the straightness checked and maybe corrected by going undersize on the mains too. All journal will also undergo a final polish.


Given the state of the bearing inserts on the big ends I was worried about what that may have done to the bores in the rods. I made a quick check of the bore diameter with tight but not fully torqued caps and found them all to be very similar. It will be interesting to repeat the measurement with fully torqued caps next week.

Incidentally there is no specification in the manual for this diameter and even a call to Lotus didn't really give the whole answer. They did give me the OD of the big end bearing but since this will be subject to an amount of crush the real diameter will be somewhat less than this. It may even be this dimension was never intended to be perfectly round [3],[4]. On the untorqured measurement the vertical was consistently 1 thou smaller than the bearing OD and 1 thou more at 90 deg.


So the next thing to do is check straightness which I'll leave for the machine shop, though a closer inspection of the wear patterns on the major an minor thrust faces [6] of the piston will be useful. Then get the old pistons off and check the fit of the new gudgeon pin.


Closer inspection of the liners revealed they were worn beyond spec on the major thrust face and were actually quite heavily scratched too. Pretty easy to remove by tapping them with something soft.


Inspecting the surface where the liner seals to the block showed some signs of leakage here and plenty of corrosion. There also seems to be an excessive amount of sealant considering it is really only of any use over the joint surface



So, new liners it is then. I plan on fitting the iron replacements available at a surprisingly reasonable price from lotusbits. Interestingly, looking back at the history all 4 liners were replaced about 30k ago with second hand items - may explain all that sealant. Looking back at some old post it would appear that the piston-liner clearance should be that of the LC so I may just be lucky and find that the ID of the new liners is suitable otherwise it is another machining task to get this dimesnion to spec.

Block Cleaning

Gradually getting there with this one, the worst of the gunk is off so at least I don't get quite so filthy when working on it. The threads clean clean up nicely after running a tap through them and I've found Fuchs gasket and paint stripper to be reasonbly effective at getting the silicone sealant off




Still a fair way to go, the core plugs need to come out and all those oilways need to be spotless. I then want to mate the two pieces together and check the main bearing bore diamters.

Water Inlet

At the bottom of this old thread somebody recommended that the water inlet in the block be opened up. Looking at this area in my bloack Im wondering if this has already been done, can anyone remember what theirs looked like?


[1] Clevite Bearing failure guide here

[2] Engine Builders Handbook, Tom Monroe

[3] Back to Basics, Bearings, Larry Carley. here

[4] Field Application Note, Journal bearings. here

[5] Piston-Bore clearance, Guy Croft. here

[6] Thrust Faces and Lubrication, KB Pistons. here

[7] Clevite Master Bearing catalog. here

Edited by _ambrose_
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