making my own cam tower shims

[brownclee]

I'm is the beginning stages of building a new L28 engine for my Z-car project. I've decided to do the "0.080" mod (as described by http://datsunzgarage.com/p79/) to raise the compression to 10:1. I'm using a P90 head shaved 0.075" (to reduce combustion chamber volume and raise compression) on the bottom and 0.005" on the top (to ensure the cam tower mounting faces are all flat).

After searching in vain for a suitable means of shiming the cam towers, I decided to make my own. I searched for and found aluminum sheet stock that is 0.080" thick. My biggest concern was the tolerance of the thickness of the plate. I found plate that is +/-0.0015". It is 7075 T6 aerospace grade (http://www.onlinemetals.com/merchant.cfm?pid=12661&step=4&showunits=inches&id=916&top_cat=60). I ordered a 12"x12" sheet which is plenty plus some extra for screw ups....which will happen. I used my digital caliper to measure the plate and it measures between 0.079" and 0.080"....outstanding!

Then I set out to cut the shims out. I decided to drill holes in the sheet first and then cut the shim out. As a guide, I traced the base of the cam tower in the sheet with a permanant marker. Nest, I used a used a drill bit that is slightly smaller than the tower mounting bolt hole to use a marking guide for the first hole....tapping it lightly with a hammer then turning it about 90 degrees and tapping it again. The leaves and "x" mark on the sheet than can be used as a guide for and good center punch mark after moving the tower out of the way. After punching the plate I used a drill bit that is just slightly larger than the tower dowel. Using a drill press and a piece of wood as a backer, I drilled the first hole. Then using the dowel in the tower to reposition the tower back on the plate and and used the fist bit used above to mark the other mounting hole center. Again, marking it with an "x" and punching it I drilled it with the second bit. This did not create a perfect fit but with very little filing, I managed to slightly enlarge the second hole and the the tower with dowels fits perfectly to the plate. I then used yet another drill bit to mark the larger hole for the head mounting bolt that is also in the tower and drilled the plate. I was amazed at how nicely all three holes aligned with the tower with minimal filing. I then used a nail that fits into the oil hole to mark the plate for the oil passage and drilled the plate.

Using the outline of the tower previously marked on the plate, I used a band saw (equiped with a metal cutting blade) I roughly cut the shim out of the plate and used my bench sander and files to clean up the shim. A utility knife with a light touch can easily clean any burrs at the edges of the holes. I have only competed on shim so far and it took me about an hour. I'm sure the next four will take less time. I will post more info as I learn more.

Edited January 6, 2011 by brownclee

[cygnusx1]

I always love the DIY stuff!

[Derek]

Hi

I know this is a bit late but I sell cam tower shims in .080" and .063" They're cnc machined from 7075. But on the up side you saved yourself $100.00!

Make sure you debur everything really well and when your torquing down the towers keep spinning the cam to make sure it's not binding.

Derek

[5thhorsemann]

I don't think its a good idea to use aluminum shims, they will crush when torque is applied. Go to McMaster carr and get stainless steel shimstock. High tolerance, no crush factor, and reusable with excelent repeatability. Afterall, you may have to do things twice, if you use aluminum you will not get the same result the second time. Just my 2 cents.

[brownclee]

Derek,

Thanks for the for the pointers. I think I'll have about $40 and 6 hrs. in the shims. Cost was a big driver behind my doing it myself. However, I'm sure they will not look nearly as nice and the CNC ones you make. But once the valve cover is on, who's going to see them. I too used 7075 because the thickness tolerance is so low. I don't foresee any issues with the cam shaft alignment. I'll keep you posted.

[Derek]

I don't think its a good idea to use aluminum shims, they will crush when torque is applied. Go to McMaster carr and get stainless steel shimstock. High tolerance, no crush factor, and reusable with excelent repeatability. Afterall, you may have to do things twice, if you use aluminum you will not get the same result the second time. Just my 2 cents.

I think you'd be hard pressed to crush .080" 7075 with 54 lb head bolt torque alone. Plus the expansion coefficient is equal with the aluminum whereas the stainless isn't.

And that's my 2 cents

Derek

[5thhorsemann]

I think you'd be hard pressed to crush .080" 7075 with 54 lb head bolt torque alone. Plus the expansion coefficient is equal with the aluminum whereas the stainless isn't.

And that's my 2 cents

Derek

Point taken, I still prefer the harder metals for shimstock, even in low torque applications. More so when you are trying to match thickness at several different points. I never had to do the job described here, so I'll just shut up now.

[Diseazd]

I have a brand new set of .080 inch shims that you can have.........It's missing the number 1 shim. If you want them, PM me......they're yours. Happy New Year.........Guy

,

"

[Diseazd]

Edited January 8, 2011 by Diseazd
Mistake

[brownclee]

So far so good. I finished making the shims today. I was careful to make sure that they matched the exact profile of the cam towers and debured all edges. Overall, it was a much less difficult job than I had anticipated. The most difficult part was making sure the holes lined up. Like Derek, I am not concerned with crushing the shims. They are pretty thick and 7075 is one of the highest stregth alloys you can buy. Besides, I could not have made them from stainless in my shop. Stainless is very hard and much to difficult to machine with the simple tools I have.

To test my handy work, I thoroughly cleaned everything, chased the bolt holses with a tap and installed the towers and camshaft. I coated all the cam journals with assembly lube and had the cam in place before installing the bolts. I sungged all the towers starting at the middle and working out in several steps. Then torqued all the bolts to a relatively light torqe (8 ft lb). The cam turns perfectly with no binding....horay!!! The head is not on the block but I don't anticipate there being issues after the head bolts are installed. I'm going to replace the tower bolts with ones that are 5-10mm longer. There is very little thread engagement without the shims and 2mm less with them. I have checked and there is plenty of depth for the longer bolts. I'm not sure why there is so little thread engagement with the factory bolts. Without the shims, there appears to be only 6-8 mm thread engagement. The rule of thumb for alluminum threads is at least 2 x diameter....in this case 16 mm. My longer bolts should be better than factory but not quite the 16mm goal. I am very pleased with the results. I only have $30 in the shims and now my cam will be in the correct position relative to my crank.

Edited January 9, 2011 by brownclee

[LeonV]

Digging this up because of the very useful info in this thread. I was looking for .080" 7075 shim stock and the link in post #1 is perfect, just ordered some. Cost me just over $30 shipped for a 12"X12" sheet.

[RPMRacing]

Hey Derek, do you still sell the .080 shims? i need a set ASAP