3404speed
Ancient Decrepit Member
Did you set the valve lash yet? This made a tremendous difference in mine, idle smoothed out nicely. Read Slantsixdan's links on valve lash adjustment...posted many times
I have a 1975 Lull rough terrain forklift with a 225 Chrysler industrial gas slant 6 engine (!) The engine smokes badly (blue smoke) and burns oil. It does not smoke at start up; it only starts smoking after running for ten minutes or so. The compression readings are 120-125-120-135-145-120. From what I've read, these are pretty healthy numbers and are (just) within the +/- 25psi rule. I'm guessing that the problem is worn valve stem seals. My question is, with these compression readings, should I not even bother with a full valve job, and just replace the stem seals without removing the head? The engine runs like a champ otherwise. Thanking you in advance for input.
It has a miss, once in a while you hear a slight pop at the tailpipe, could it be a burnt valve, or maybe I need to redo the valve lash adjustment?
:thumbrig:
unless all the vacuum from the running cylinders at idle opens the throtle valve a bit, but I dont think this happens
Is it just me, or do I kill a lot of threads?
My guage reads a bit low. Even on my freshly built yamaha xs650 engines I get 100 or so. LLeak down passes with flying colors on the guage. My slant has a slight rough idle and I could only get 100 psi or so on the guage. But with a leak down it was more than acceptable. So could be the reman. Holley 1920 on it. It's not real bad for roughness so I just kind of ignore it for now. Also have black plug on 6. Clean for half of the porcelain but black for the other half to the threads. Car doesn't seem to use oil. No smoke while dad follows me...float height is good. Kind of a mystery I haven't figured out yet that may also be related to my slight idle quirk.
So....I would leak down test anyways.
So what do you consider acceptable?
I'll tell you my acceptable;on my guage. zero to 4% maximum.
You say; What! Hey I don't make stuff up. This is straight off the pages of Smokey Yunichs Power Secrets. A brilliant mechanic and racer of yesteryear.
At 8% that cylinder is toast. At 6% she is no longer performing anywhere near her potential.And bear in mind that a leakdown test is a snapshot of leakage at TDC only. From a few thou down,the cylinder could be split wide open, or the wrist-pin could have left a deep gash in the wall,and the gauge would still read A-OK. But at least you would know that the valves are closed. Likewise, the guides could be wore right out, or not even in there, but at least you would know that the valves are closed. The LD test is a snapshot. It's up to the tech to figure out the rest of the story.
125-135 psi is NORMAL for a stock 225 /6 motor in very good condition. I got 130 psi +/- on all cylinders with a solid, fresh rebuild with fresh bores, pistons, and moly top rings, the head shaved a bit, and a very mild cam. The compression ratio is just not there for higher numbers in a stockish /6. And yes, the throttle being open vs closed makes about a 5 psi difference on a /6.
Acceptable leak down %? I gotta laugh about this one. 4 cylinder piston aircraft engines are allowed far,far more leakage than is being cited here when cold! Something like 30%!
Woah - I wonder now after reading this thread if my newly-built /6 has too much compression. I decked the block 0.050", and the heads 0.030", aiming for about 9.5:1 compression. Pistons are +0.030", too.
All six cylinders are within 3.5% of each other, with an average of 194 psi. Wet. Throttle tied wide-open. High-torque starter from a late-model Dodge V8 motor. All spark plugs removed for the testing.
It's only been driven for 10 miles, and I know the stock distributor is having problems that I suspect are tied to the centripetal weights seeming to have worn springs. Even with the adjustable bracket at the bottom of the distributor bottomed-out in its slot, I couldn't get base timing at idle to be less than about 8 degrees BTDC. Was aiming to get 0 or 2 degrees (with vaccuum line disconnected).
And it's got fairly bad 'clatter' / pre-ignition at wide-open throttle. With 89 octane fuel only, so far.
Wondering now if I did the math wrong and ended up with a 10.5:1 motor??
I have a rebuilt distributor I'm installing in a few days. Be curious to see if it helps.
Woah - I wonder now after reading this thread if my newly-built /6 has too much compression. I decked the block 0.050", and the heads 0.030", aiming for about 9.5:1 compression. Pistons are +0.030", too.
All six cylinders are within 3.5% of each other, with an average of 194 psi. Wet. Throttle tied wide-open. High-torque starter from a late-model Dodge V8 motor. All spark plugs removed for the testing.
It's only been driven for 10 miles, and I know the stock distributor is having problems that I suspect are tied to the centripetal weights seeming to have worn springs. Even with the adjustable bracket at the bottom of the distributor bottomed-out in its slot, I couldn't get base timing at idle to be less than about 8 degrees BTDC. Was aiming to get 0 or 2 degrees (with vaccuum line disconnected).
And it's got fairly bad 'clatter' / pre-ignition at wide-open throttle. With 89 octane fuel only, so far.
Wondering now if I did the math wrong and ended up with a 10.5:1 motor??
I have a rebuilt distributor I'm installing in a few days. Be curious to see if it helps.
Is this a 225, 198, or 170 ci /6? I think I would try another compression gauge first; 194 seems awfully high for the mods you have done. The pistons are still in the hole a good bit with .050" off the block for a 225. If need be, you could put in a thicker head gasket. Which one did you use in the rebuild?
The ignition timing thing looks to me to be that the distributor is off a tooth, or you need to monkey with the timing adjustment on the bottom side of the distributor body. You should be able to set it anywhere you please.
I'd be putting in some 93 octane to see if the clatter goes away, and stick with
that until you get things sorted out better.
What carb do you have? Do you know the year model of the carb? And under what conditions do you have the pinging?
Woah - I wonder now after reading this thread if my newly-built /6 has too much compression. I decked the block 0.050", and the heads 0.030", aiming for about 9.5:1 compression. Pistons are +0.030", too.