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dggt6

Extra Thrust

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Greetings Gents,

Thought I would throw an idea into the ring for some comments.(hopefully nice ones!!)

Adding an extra thrust washer seems like a nice idea.

Drilling and tapping for little brass screws seems annoying.

Having to remove the crank to replace thrust washers seems VERY annoying.

How about adding 90% of an extra washer and no "pinning" or screwing?

 

I followed the basic idea of what Fred Griffiths suggested.....

http://www.oocities.org/motorcity/speedway/1080/thrustwasherinstall.html

BUT I started machining from the middle and did NOT go all the way out to the ends.

This leaves the edge of the bearing cap in place to stop the original washer from rotating as per original design.

The extra washer can be cut down to fit into the new recess in the bearing cap and does not need to be pined/screwed.

 

Yes, OK, not pinning the washer still allows a very worn washer to go swimming but this method should almost double the time between swims!!

 

I bought a 6mm HSS 4 flute end mill and it cuts the bearing cap quite easily. My drill press is a typical 12 speed home garage type and managed it well. I did re-check that the table was bang on 90 degrees to the drill bit.

Moving the bearing cap by hand was not as difficult and scary as it may sound. Just take light cuts and hold tight.

Getting the depth accurate enough to match the recess in the engine block may be tricky but we will see soon enough.....

 

Cheers,

Doug

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I've done a couple myself in the past,first one using brass screws to retain the bearing,second one more like yours.

the owner has long since sold the car with the first but mine is still going ok so far(touch wood).

 

don't like the sound of holding the work piece  by hand though :no:

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Hi Esxefi,

Glad to hear you haven't had any trouble with your non-pinned washer.

I do have a healthy regard (scared) of tools that wizz around but after starting with a VERY shallow cut I realised it wasn't going to jump up and drag me in!

I felt it was no more risky than operating a scroll/bandsaw , wire brush on a grinder or a router (wood).

Yes you need to be very careful and take all precautions. You could try and make a jig to hold the cap so your fingers are further away from the cutter.

The cast iron cut very nicely and more "smoothly" than I expected.

 

Cheers,

Doug

 

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Hello Doug,

 

have you thought that putting thrust bearings on the cap puts a force on the cap which it is not designed for? The cap is very strong in a vertical plane but less so horizontally..

As  a matter of interest, the Jaguar XK engine also uses exactly the same thrust bearing arrangement, i.e. halve bearings in the block only. I believe there is a good resaon to just fit halves as the cost to the manufacturer is only one pair of bearings, hardly worth saving?

 

Yes, cast iron machines very easily but you get black from it due to the large amount of carbon in it.

 

Alec

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Hi SpitMk11,

here are a couple of photos of my drill press/ pillar drill. Definitely not a milling machine but apparently good enough for this job.

I tried to make the jig as rigid as possible so I could push quite hard if needed to keep the cap against the circular former.

 

Hi Alec,

interesting and accurate thought! I had not heard that argument for NOT doing this modification. Perhaps I should machine both sides of the cap!!!! :)

I had "presumed/assumed" that the cap being a tight machined fit into the block and torqued up would be up to the task especially as it would only be taking about 40% of the "load".

A bit more thinking required me thinks. :wallbash:

 

Cheers,

Doug

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Hello Doug,

 

sideways force will try and bend the two claming studs, it is the weakest part of the journal as far as resisting force. From a machining point of view you need to be very accurate as to the depth otherwise the new bearing will take all the thrust or none at all until the bearings wear to an equal plane.

 

I overhauled my fairly hard driven 2.5 engine recently and although the big ends and mains showed signs of wear and were replaced, the thrusts were good to go again. This is at about 45,000 miles, oil pressure was still very good.

 

Alec

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HI Alec,

I totally agree with your assessment that the current arrangement was NOT designed to take a side load. I initially was thinking that the crank would be pushing on the "top" of the bearing cap and would therefore require little force to "tilt" the cap, thus bending the bolts and munching up the bearings and crank.

On second thoughts, I realised that the crank could not apply more pressure to the top of the cap as it was held perpendicular by the original thrust bearing, thus most/all the force would be applied "evenly" across the new thrust/cap. The force applied would actually be a "direct" "shear force" against the bolts. Once again, bolts are not designed to take a "shear" force.

So how much force is 40% of "clutch  pressure" and would it have more negative effect than the positive effect of having an extra 40% of thrust bearing surface?

I don't know.

WARNING. Anyone/everyone reading this article make your own decision about whether to attempt this modification. It is a gamble making something do it wasn't designed to do.

I am going to go ahead and  try it in the name of experimentation (and I am already set up to do it) and acknowledge it may break my engine.

 

Lets hope the force is NOT strong with this one!

 

 

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The thrust loads from the clutch are pretty small in the scheme of things.  I'm sure the cap assembly is well able to handle the load. It's only the lack of bearing area and rather feeble material used for the bearing that causes problems.  In my view starting the engine with the clutch down is a factor too.

 

Similar mods have been done plenty of times on 4 and 6 cyl, but usually with the additional washer held on with brass screws.  I like this method but agree that machining accuracy is important.

 

Nick

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Well I went and dog-gone dun-it I did.

It went surprisingly well.

I had just on 0.03mm end float on my freshly machined crank.

With the bearing cap torqued up and (gently) tapped forwards, I measured 1.05mm between the cap and the edge of the crank.

The std thrust measured 2.36mm thick. Subtracting the gap of 1.05 gives 1.31mm for the depth of the groove.

I took about 7 cuts to get down to 1.34mm. One end of the groove was a fraction shallow so a slip of paper under that end and another pass of the cutter evened the groove out to 1.34mm.

I ground the ends of the washer down to fit.

My feeler gauges only go down to 0.004 and I couldn't get that in between the original washer and the crank.

The cap and new washer slid in snugly.

After torquing up, the 0.004 feeler blade "almost" started to fit in.

The dial gauge still gave me 0.03 end float.

 

If things go to plan, these washers will out live my ownership of the engine/car!!! Not because of he skilled engineering but because my car spends more time being worked on that actual driving!!!! The car is on a special registration and so far I have not had the car on the road any more than 30 times in the last 2 years. :Build_it:

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on talk of bolts not designed to take a shear force the wishbone and rear radius arm bush bolts are loaded exactly like that,yes the thread clamping load should ideally be preventing bush tube movement but it won't be enough to prevent the tube from applying a side load on the bolt shaft,they are only 3/8" diam after all.

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