Derek's 308 engine rebuild

To weigh the big ends while I was lightening the heavier ones, I mounted and old piston pin on my dial gauge base as a small end pivot and then raised the scale to give a horizontal rod. Nice idea but in practice sliding the rod on and off moved the base slightly (even stuck down with press-stick.) This made it hard to get the precision of 0.2g I had with placing the end centres on stuck-down toothpicks so I went back to that system. Since it's a flat plane crank and bob weights aren't used to balance the crank, accuracy (the actual weight) is not important but the precision is (repeatability and relative weight.)

I started with the Dremel but it was very slow so I used a fine flap-wheel on a small angle grinder which worked very well. Two rods were almost 4g off and the next five needed 1-2g to match the lightest BE.
Image Unavailable, Please Login

 

I noticed that one of my rod caps has a small area of pitting adjacent to the bolt. While it is not a high stress area I'd rather get another rod or have it re-sized to take off a couple of thou. Does anyone have a conrod they can spare (max 575 grams?) Thanks!
Image Unavailable, Please Login

 

That is 575g incl. bolts/nuts. C or D rod needed 528-536g without bolts/nuts. Can trade for $, cheap Chinese parts, or 12yr single malt Scotch

 

Patrick, I can have the rod resized a little by grinding a small amount off the cap mating surfaces and then honing round to spec with a big end hone. This eliminates the pitted surface. Unless I find another rod soon that is what I'll do.

Cheers derek

 

That's very kind of you Dave but I think the post might be expensive and risky (are they still on strike, or in the shower . Let me try here in N. America for a few more days. Cheers derek

 

I'm an ex-Ikey (College House) and Hilton before that. Mum in Knysna, sister in Plett. Watching and hoping for you guys...

 

Took it to a well respected local machine shop and he said the pitting will disappear with the resize. He'll do it once I have the new ARP rod bolts as several have suggested that they are a bit tighter than the original bolts so better to resize with the new bolts. He'll check all the rods while the machine is set up for 47.13mm BE and 18.5mm SE.

Someone asked me about dynamically balancing the rotating assembly with bob weights. They had paid a reputable engine rebuilder for this service and pointed out that others in this forum have suggested previously that bob weights are needed to balance the crank. Perhaps I'm mistaken but I always thought that flat plane cranks don't need bob weights due to their geometric symmetry (as in a straight 4-cylinder, adjacent pairs cancel out each other's primary imbalance.) The secondary imbalance can't be helped without balance shafts which is why our rods can be as varied as they are-- imperfect primary imbalance is not noticeable due to the secondary imbalance vibrations (i.e. my balancing efforts on the rods are not going to be felt.)

 

As some of you may have heard, we have been having a lot of rain and boating season has come early to our neighbours across the Ottawa river with over 400 homes flooded. I was sick of waiting for a hot day so soaked the heads with Gunk gel for a few hours and then blasted them with the pressure washer to get rid of any last dirt, dust and porting debris. Put them in a warm oven with the fan on for an hour and they are ready to put the valves, springs, lifters, cams in.
Image Unavailable, Please Login
Image Unavailable, Please Login

 

I started assembling the heads and wasted a stem seal when I forgot to put the spring seat into the 3rd valve I did. Decided it was better to put all the spring seats in place before doing a single stem seal. I'll put two extra viton stem seals in any sets ordered from now on.

I found that the easiest way to press on the seals was with an appropriately sized socket on an extension that you can press down with while moving the extension in a circular motion to work the seal over the guide. Oil them first and check they are straight and all the way on afterwards.

My trusty home-made spring compressor works well and saved me a drive out to the tool supply shop. It's an old, blunt hole saw attached to a C-clamp with some access holes cut out of the sides with a cutting disk (to allow the collets/keepers to be pushed into place.) Careful not to compress too far as you can damage the seal.
Image Unavailable, Please Login

 

... the "appropriately sized socket" should only press down on the steel shoulders of the stem seal. Oil the valves before you put them into the guides and I smeared some assembly line on all the valve seats which rust if you just look at them.

 

All the valves are in. I used Comp Cams assembly lube on the valves and guides but may put a little bit of moly/zinc cam paste on the tips, tappets, cams. I've seen how rings don't seat with the use of moly but I plan to dump the oil after 30 minutes so the assembly lubes will mostly be gone. Any thoughts on this approach?

I got a set of 100 valve shims (3.3-4.7mm) from Autopartsways.ca. For a change something was cheaper in Canada (Partsgeek has them in the US.)
https://www.autopartsway.ca/partdetails.cfm?w0133-1604802/crp
Image Unavailable, Please Login

 

... if anyone is doing a rebuild or valve adjustment and needs shims, send me a PM with the thicknesses you need.

 

I spent a couple of hours adjusting the valve clearance. Everything takes longer than expected-- partly me being a beginner (and not that smart sometimes) and partly the peculiarities of the engineering.

I spent a while trying to figure out why my one cam was a bit tight. Loosened the caps in turn and found the two culprits. The journals looked fine so I mic'ed the cam journals, put a bore gauge into the caps-- no problems. Then I notice that a couple of the caps have their ID numbers on the inside whereas the rest were on the outside. I had used the casting numbers on the cap tops, assuming they would all have been assembled in one direction. Once I put all the stamped numbers on the outside, all was good.

Another hiccup is that two of my exhaust valves are a little tight with 3.30mm shims so I have to get some 3.20 and 3.25 shims (my set starts at 3.30.) Does anyone have a few thinner shims I can buy/swap. If not I'll buy some from an online Fiat, BMW, or Volvo parts dealer. I think the combination of the new valves and cut seats have pushed the tips up a bit. I checked my Cat cam lobes (10.75mm lift) and they still have plenty of space to the edge of the shim but the 13mm lift lobes must be close.
Image Unavailable, Please Login

 

Brian, The BMW S14 and S38 have shims down to 3.00 and some of their variants had pretty big cams and high seat pressures so I'm not worried about using 3.20 and 3.25mm. When I have a chance I'll check the cam base circle, it may be a little bigger and those two valves perhaps a touch longer. The seats all looked really good (my machinist barely touched them when he cut them.) I check again tomorrow.

As the valvetrain wears, do you need thicker or thinner shims generally?