| Author | Message | ||
| Bill Tipton (Sleeper)
New member Username: Sleeper Post Number: 1 Registered: 12-2002 |
Dude, Here is the thread for your perusal and comments. As you know I am interersted. Bill T. | ||
| '75 308 GT4 (Peter)
Intermediate Member Username: Peter Post Number: 2448 Registered: 12-2000 |
Air injection essentially adds more oxygen into the exhaust-gas stream. This assists to consume more CO and turn it into CO2. It also elevates the temperature of the exhaust gas (from the process of CO to CO2) and therefore affects the valve itself (as its exposed to that increase of heat). This is one of the reasons why they used sodium-filled valves on the exhaust side (sodium absorbs the heat). Without the air-pumps, there's no increase in heat, so the sodium valves become redundant and potentially dangerous (as they wear, they're prone to rocking and will bend and break if they strike the cut-outs on the piston crowns). | ||
| Kelly (Tifosi1)
Member Username: Tifosi1 Post Number: 483 Registered: 2-2002 |
Sorry but I disagree. The purpose of the air pump is to add oxygen to the unburned gas and let it burn in the exhaust pipe. The air pressure going into the exhaust has to have enough pressure to be added to the mix of the back pressure caused by the cats and the muffler. So, you get less gas in the exhaust and a cleaner running engine. there is no way i would believe that the air could make it up from the exhaust gas coming out of the exhaust valve to cool the valve. I just don't see it. It would be like adding water down stream of a river hoping to add enough to cool the upper part of the river. My 2 cents Kelly | ||
| David Lewis (Davidlewis)
New member Username: Davidlewis Post Number: 44 Registered: 2-2002 |
(possible cause -- car run w/o the air pump. one of the air pump function is to cool the valves.) Is this a generally accepted conclusion to running w/o the air pump? I've driven with the belt off to see if there was a power difference (there wasn't). How soon are you in danger? | ||
| 82 308gtsi (Gary_t)
New member Username: Gary_t Post Number: 9 Registered: 1-2003 |
Thank you all for the info. My father and I managed to pull the engine straight out after we removed everything. (including muffler,rear axles,even the engine-chassis mounting plates) After that remove cylinder head became an easy job. I have both heads rebuilt even though only 5-8 cyl. had problem. However, it turned out all 16 valves need replcement b/c all valve stems were too thin. (possible cause -- car run w/o the air pump. one of the air pump function is to cool the valves.) Anyway this whole episode cost me about $2,600.(16 valves, guides and stem seals cost about $1,000 that I provided to the machine shop. Another $900 for all the gaskets, cam seals, and timing belts to complete the job. The machine shop charged me $550 for the labor. ) The labor my father and I for disassembled/assembled the engine are free. I am sure that I have saved tons of money by doing all this myself. But this sure takes a lot of time to complete the job -- 4 months. | ||
| billy bob (Fatbillybob)
Junior Member Username: Fatbillybob Post Number: 166 Registered: 8-2002 |
You can put the car in 2nd and unhook the shifter. Unhook both hearders and engine mounts tilt the engine back about 90 degrees on the cherry picker using climbing rope. Then pop the head off. If you scored the piston and cylinder do it right and pull the engine the rest of the way. It is actually a simple rebuild and will be more of a known quantity that an unknown pull out motor. | ||
| Robert Johnson (Carb308)
New member Username: Carb308 Post Number: 24 Registered: 12-2001 |
Just a note I hope is not too far off this post. In 1975 on a trip with a friend of mine from Tucson to Phoenix in May, in my dad's 56 GMC 1/2 ton Stovebolt six Pick up I spun #1 Rod at about 105 MPH. Stopped on the shoulder of I8 & dropped the pan. I has some emery cloth in my tool box and used it to "refinish" the crank. Removed what was left of the bearings from the rod and removed my belt. Cut a "new" bearing from my belt, punched an oil hole in it with a phillips screw driver. Put the cap back on and tightened the s**t out of it. Put the pan back on, (didn't leak any worse than before). Never told my dad. He kept the truck on the ranch for another 2 years without any problem, (no more speed runs in it by me). Sold it and it ran until we lost touch with the next owner. I would not try this on my Ferrari, but it worked for me one hot day when I had ti see a girl in Phoenix and was broke. Ah to be young again. | ||
| Hans E. Hansen (4re_gt4)
Member Username: 4re_gt4 Post Number: 814 Registered: 4-2002 |
You'll crap if I tell you what the 'fender washer' repair was on. FWIW, these were VERY low revving engines. And, yes, you are right. Leather belt was a viable bearing repair way back in the days when no one had any money. Moonshine? Would probably work, but given the two possible places to pour it into, it probably wouldn't make it into the gas tank.  | ||
| JRV (Jrvall)
Member Username: Jrvall Post Number: 642 Registered: 11-2002 |
>>a couple of fender washers and a bolt in a piston << and a length of leather belt works great when your rod bearings go out. and when you run out of gas just fill the tank with Moonshine. | ||
| Hans E. Hansen (4re_gt4)
Member Username: 4re_gt4 Post Number: 808 Registered: 4-2002 |
I kinda wondered about that....... FWIW, an old mechanic friend of mine once used a couple of fender washers and a bolt in a piston way back in the depression era. | ||
| '75 308 GT4 (Peter)
Intermediate Member Username: Peter Post Number: 2406 Registered: 12-2000 |
Welding cast pistons... Ooooo sketchy....  | ||
| Erik R. K. Jonsson (Gamester)
Member Username: Gamester Post Number: 256 Registered: 11-2000 |
FWIW I did the rear head in car on a GTBi for under $1000 complete. All new seals, valves, valvejob, headgasket, cam gasket and seals. One piston had a perfect hole in the center from the valve stem puncturing it, had Hi Tech welding TIG the hole in car while I held the ground to the top of the piston. Has held up nicely and saved a ton of time. (thanks Ric for the piston) | ||
| Paul Newman (Newman)
Intermediate Member Username: Newman Post Number: 1019 Registered: 12-2001 |
Thats a good idea david but since the valve is broken and sideways in the cylinder, I would think the piston and liner may be mangled anyway. If I had to do a head gasket only, I would consider doing it in car the way you suggested. | ||
| david wilcox (Dwspeedracer)
New member Username: Dwspeedracer Post Number: 1 Registered: 1-2003 |
I had to remove the lower row of valve cover and cam studs but if I would try removing motor mount bolts then slide engine back a few inches it might save you from removing the studs | ||
| Drew Kelley (Drew)
New member Username: Drew Post Number: 6 Registered: 1-2003 |
Here's a tip: the only way to get the 5-8 header out of the way is to pull the fuel tanks. Otherwise, you have to lift the engine/transaxel assy out with the header lying loose in the engine compartment (it has to go back in the same way). Also, when lifting the assy, it has to be rotated 90 degrees towards the rear of the car (the sump plates have to be facing forward) or the assy won't clear the opening in the bodywork. It's a lot of fun. | ||
| Paul Newman (Newman)
Intermediate Member Username: Newman Post Number: 1015 Registered: 12-2001 |
The used route sounds good and you can part out yours to recover some of the cash. Maybe keep the matching block though. | ||
| Terry Springer (Tspringer)
Member Username: Tspringer Post Number: 371 Registered: 4-2002 |
Yank that lump out, call T Rutlands about a good used engine and you can be back on the road in weeks for not that much $$$. | ||
| Steve Magnusson (91tr)
Intermediate Member Username: 91tr Post Number: 1310 Registered: 1-2001 |
Gary -- Sorry to hear about your difficulties, but I think we've all got more "experience" (the hard way) than we'd like -- good luck with the repair... | ||
| '75 308 GT4 (Peter)
Intermediate Member Username: Peter Post Number: 2380 Registered: 12-2000 |
Gary, get your cherry picker, engine stand and cheque book out...  | ||
| 82 308gtsi (Gary_t)
New member Username: Gary_t Post Number: 8 Registered: 1-2003 |
Steve -- One thing for sure, I saw the #6 intake valve already broke and now sitting/jammed side way at the base/valve openning area. #5 valve's stem slanted off center which cause the valve only closed partially. #7&8 seem OK. Can I take anymore bad news? I'll busy this weekend. Thanks you for your response. | ||
| Steve Magnusson (91tr)
Intermediate Member Username: 91tr Post Number: 1308 Registered: 1-2001 |
Getting the 5-8 cyl. head off a 308 2-valve with the engine still in the chassis would need a minor miracle if it's possible at all -- maybe if you removed/unthreaded the studs first (probably another near impossible task), but cleaning/dressing the block surface and reassembly wouldn't be very easy either in that configuration so I don't think you'd be saving any work/aggrevation. Just getting it off even with the engine out can be a major b*tch. Did you confirm something was amiss with the relative cam/crank phasing to cause your problem? | ||
| 82 308gtsi (Gary_t)
New member Username: Gary_t Post Number: 7 Registered: 1-2003 |
I reset the timing and started the engine. after few minutes, it sounded very crapy. Cylinder 5-8 have no pressure. I have loosen the cylinder head 5-8, but can't get it out because there is not enough space to completely clear away from the 10 extruded screws. Looks like engine needed to be out in order to remove cylinder 5-8. Anyone did this before? Is my conclusion correct? |