Derek's 308 engine rebuild

I just measured the combustion chamber volume and dome volume to get a quick idea of my static CR. 348 crank is a 75mm stroke, bore is 81.25mm so swept vol is 398.5cc. Chamber is 42cc and piston dome-- measured with tape around the top, water, and subtract the water from a cylinder to get the net dome vol. of 9,3cc. My JE pistons have a lower compression height as they were originally made for a turbo build so with the head gasket I have another 1.8cc so a total combustion volume of 42-9.3+1.8=34.5cc which gives a static CR of 12.55:1 and with the Cat cams inlet closing at 70 degrees after BDC the dynamic CR will be 9.45 which is too high for pump gas (want to be under 8.5.) I need to have a net combustion chamber volume of about 39cc so will need to lose 4.5cc from the chamber and piston (or use shorter rods.)

I ordered an adjustable reamer and will fit the pistons to the rods next week and do a test assembly since my calcs above were based on the numbers for std pistons and deck height in newto308's piston tips thread. Once I have the actual numbers for my motor I'll run the calcs again and decide what to do.
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I lapped the valves and the seats show up nicely against the black nitride. Tomorrow I'll back cut to leave 1mm seats on the inlets and 1.5mm on the exhausts. I'll also smooth out the sharp edges on the outside of the seats. I'll spin the valves in my drill press and use a dremel tool to remove material where needed.
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Helder, the car sat in a garage for 16 years plus it still had the sodium-filled exhaust valves. 58k kms, bores were near the limit and valve guides were past the limit. The crank was ok but I bought a 348 crank which needed grinding. There were also signs of coolant migration through the head gasket and past the manifold gaskets into the ports.

 

Back cutting was easier than I expected. I found the sandpaper tubes on my Dremel worked the best and did the sharp edges around the edge of the valves with a fine diamond file. One thing I noticed is my drill press chuck is not very concentric so I turned the valve in the chuck every 30 seconds and it took about two minutes per valve. Well worth the effort!
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Patrick, I thought it would be hard to control and I might touch the seat and have to re-lap or toss the valve. It was actually quite easy as I used the slowest setting on the drill press, pressed lightly and let the sand drum follow the valve movement. There was very little heat since removal was slow-- when I rotated the valve in the chuck it was slightly warm but nothing that could affect 21-4N. I blended the back of the head around into the seat for a smooth, undisturbed flow. Cheers derek

Ps I think I may owe you a few beers unless I kick it into a higher gear! The reluctance to eat my own words has been a strong motivator so I probably owe you a beer or three anyway.

 

I managed to port one head today and match the manifold. It is slower and takes longer with the dremel, not as much power as a die grinder but my little compressor is too small and too noisy for the basement. I just smoothed all the transitions and widened the short side radius a bit. I also blended the inlet guides a bit (just a few mm.)
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I look forward to the sims Rob. Are you able to model the fuel and ignition as I can change the Weber chokes and jets, adjust the ignition map with the MSD6350 based on rpm and MAP.

I was very happy with the German made rod bearing from Dinoparts. One was scratched in shipping and Alfredo sent a replacement immediately. The finish is better than the Superformance bearings and gives the correct crush and clearance. The ACL Suzuki G16 bearings were actually a better finish than both and look very well made. They are a different colour and totally different marking system (ACL stamped, Superformance laser) so I suspect the latter are not from Australia. They would work fine as long as you grind to suit the bearings as fitted in your rods.

Off to port the second head and not enthralled by the prospect of several hours on my feet, mask on, and super concentrated not to touch the seats. I might find a short 40mm OD tube to tape in place inside the seats to ease my mind.

 

Managed to do the exhaust ports and air injection plugs but yet to start on the second head. I torqued in the air injection plugs with copper washers, marked the protruding nose with a red marker, took them out and ground off the extra before replacing and smoothing with a sandpaper roll.
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I can get 98-99RON fuel here in Canada and in the UK if I take the car with me, but am concerned about the stresses and heat generated by going that high on the compression. I also remember reading somewhere that 93 octane pump gas requires a dynamic CR of 8.5:1 or less so perhaps 98-99 can manage over 9.0:1?

I just got some brass plugs for the oil and water passages from Duncan Rogers in the UK. Only 1.80 quid if you order 10.

Brass Internal Hex Male Metric Blanking Plug - Engineering
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I soaked the carbs in Gunk degreaser gel overnight and then gave them a good brushing with a nylon dish brush and they turned out so well I'm thinking of just blasting carb cleaner through all the passages and trying them as they are. The throttle shafts have no play at all and there is so little wear I wonder if they weren't replaced not long before the car was parked. They are a matched set 72/73/74/75 8N.
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More good news on the carbs. First I lathered soap bubble foam on and around all the throttle shafts and cupped my mouth on the bottom and blew against the closed throttle plate. I could hear air going through the idle circuit but no air came out of the sides. I even tried sucking with a vacuum cleaner and the foam piles didn't change.

Next I filled the carbs with water and all the accelerator jets were shooting very strongly and evenly. After refilling I tried to blow more water down the fill tube into the carbs but the float valves all sealed well. Finally, with the carb full and on a flat surface I measured the water level in the bowl using a paper dip stick down an emulsion tube hole and all were within 1mm of each other (25.4-26.4mm below the machined face for the cover. Does anyone know if this is correct? Can someone with a carb that is apart adjust their float and check the fuel height afterwards?

So I am not going to take the carbs apart as they are quite easy to take off if I need to later. I will probably be changing jets and chokes once it is running but I'm pretty sure these are fairly new (or newly rebuilt.)

My MSD 6AL-2 programmable arrived and a blaster SS coil so I will try to check if my stock VR sensors can trigger it individually and then in parallel.

I also got 25 feet of silicone hose from Hose Pro Inc. (check ebay) to replace the long heater hoses: 25ft 5/8" Flexfab Heater Hose 65.00, USPS Priority Mail Shipping 12.95, Total is 77.95
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Pete, I checked all of the emulsion tubes, progression holes, idle screws and seats and they were all clean. I gave all the holes, seats and passages a good blast with carb cleaner and dried them with a heater fan. I have rebuilt so many DCOEs over the years and have never seen such clean used Webers. I'm confident they are good to go and if the sniffer tubes prove me wrong later it's so easy to whip them off.

 

Hi Joe, Thanks for the feedback and comments. I was thinking of borrowing or buying a CO tester to help with the tuning (or use my old colortune kit if the plugs are visible with a mirror.)

Given the close match of the float heights and all the clean orifices, these carbs have not seen much use since a rebuild or since new so I doubt they need rebuilding. As you say, when adjusted properly the need little maintenance and I marked and counted the adjustment screws turns when removing them so I put them back the same.

Good idea to put 2 lambda sensors in the exhausts-- easy and a good extra bit of info. I'll do the same.