Predetonation on 1988 d50 2.6l and looking for weber carb. Kit

[robertson5347]

Have a D-50 4x4. Replaced the original head with a 2.6l head from a 1982 d-50. Everything matches up except the lower row of bolts on intake and solved that problem with large washers on the studs. I did notice the head from the 82 appears to be cut not as deep around the compression area around the valves as the original. My problem is twofold, I get predetonation at speeds above 45 mph with considerable loss of power when valves pinging. It starts and revs up normally when in park, but when you put it in gear it will not rev up even at wideopen throttle and doesn't have power to pull itself up a small incline. Tried adjusting the timing with very little or no improvement. Have now tore down the head due to blown gasket between the two inter cyclinders. Is my problem with compression or the carb.? It has the stock carb. on it. Someone told me that the carb. was running lean would cause predetonation. Is this possible? It appears to me that the mfg. made the 82 head with more metal in the compression area around the valves when compared with the later model. It looks like the 88 head has been machined out more and removed too much metal around the water jacket area. Could this be what makes the later model head crack so easily? How much do you think this would change the compression ratio? Your help and opinion much appreciated. Thanks

[camoit]

How long did it take to start pinging? Was it right away or did it happen over time? If it was right away then the intake has a vacuum leek. And a big one. Does the new head have the jet valves in it? Or is it the good one with out them. Also if you can post some picts of it so we can see what is going on and what you are talking about.

Oh and welcome to the board. If you need a manual feel free to down load them. We have them in .PDF

[robertson5347]

I can't remember how long the pinging has been going on. I probably put this head on about 10 yrs. ago. I know this sounds a little crazy but I only drove the truck to work and rarely got it over 40 mph due to the predetonation. For the past several yrs. it has gotten progressively worse until it just quit. That is when I did a compresson test and found the two inter cyl. at zero pressure and two outer cyl. at around 100 psi. results was blown head gasket. One thing I couldn't understand is when you throttle up in park, it sounded good and when you put it in drive and at full throttle there was nothing (like you didn't). I believe this head has jet valves. Will try to take some pictures and send you. Will try to compare both heads if I can find the old one. I do know the exhaust valves are different (believe in length) because I had to replace one when I put the head on.

[camoit]

What engine is in it. There is a stamp on the front right of the block on the head surface. It's a little tab that sticks off. Also there should be a tag on the firewall. But who knows if it was swapped to somthing different. It should be somthing like a 4G54.

Here is some info on your head. There is the usable head thickness. And CC info.

http://www.mightyram50.net/vbulletin/showthread.php/1582-G52-2-0L-Head-On-A-G54B-2-6L

[camoit]

So any updates?

[robertson5347]

No. The weather has turned too cold and I don't have a garage to work on it. It probably will have to wait to spring before I can work on it. Probably will be getting back to you with more questions then. Have a good winter. Thanks for all your help and this web site because you can't find any mechanics (whose willing to share their expertise) or info. about these older model vehicles

[camoit]

Thats why we are here. The new breed of mechanics are fun to mess with. They walk out with there computer and look so hard for a place to plug it in. Then you open the hood and you should see the look on there face. The smile just kind of melts off. Then you just tell them sorry man, the truck isn't going to tell you that part needs to be changed. It's priceless....

[Fordubishi]

LOL So true Camoit I love walking into a parts store and asking for parts for mine. When they ask what engine I have the 2.0 or the 2.6, I say the 5.0 and they tell me they have no listing for that in the computer so I tell them to look it up in the book. They give me a weird look and usually say "what book?"

[robertson5347]

I found another issue, When I went to put a new head gasket on the probably 82 head. I found a considerable difference in the diameter which was about 0.5" smaller (3.25") than the original head (3.6") that I had not noticed before. When I CC'd the head, the replacement head was 60cc's with a compression ratio figured at around 10:1. The original head was cc'd at 74 cc's with a compression ratio of about 8.6:1. Would this high compression ratio be the cause of predetonation and why it looses power above 50 mph? Any suggestions? Do I need to dump the high compression head in favor of a same year stock head?

[pennyman1]

get a head saver head gasket spacer - it will raise the head up about 15-20 /1000s of an inch and lower the compression ratio closer to stock. The 79 - 82 motors used dished pistons, the 83 -89 use flat top pistons. Your cc measurement is real close - I think the manual says 58 cc for the 82 2.6 head.

[robertson5347]

I calculated a 0.02 shim spacer would lower compression ratio to about 9.8:1. Would this be enough?

[pennyman1]

Yes but you may need mid grade or premium gas - it will run strong with higher compression