Natural Gas Engine Driven Chiller Problems

[FireBrick]

We have a TECOCHILL 150 ton Natural Gas V8 Truck engine driven screw chiller that has been giving us problems with push rods being damaged. We've had to replace a set of 4 pushrods for one bank twice.
The cylinder block is made of cast iron and has 8 cylinders arranged in a "V" shape with 4 cylinders in each bank. Five main bearings support the crankshaft, which is retained by bearing caps that are machined with the block for proper alignment and clearances. The cylinders are completely encircled by coolant jackets. The engine rating is 159 bhp at 3300rpm with a 10 degree delta T of 44*F - 54*F chilled water.

This engine was replaced 3 years ago and we recently replaced the engine oil as well. The Chiller mainly operates during swing season bet. March - May & September - November. The first time we had the push rods damaged we thought we were not giving the chiller enough of a load. Which was not the case. Once the push rods were replaced we started up the chiller at a lower rpm about 1300 rpm and gradually raised the speed. When we approached 2600 rpm the engine started to make a loud clapping sound. The end result was we damaged the second set of push rods in the same bank. The other bank of the engine received no damage to any of its rocker arm assembly. We are puzzled as to what the problem might be. We replaced another set of push rods and can only run the chiller at a max speed of 2600 RPM producing only 100 tons of cooling. So far we know the screw compressor alignment with to the engine is not a factor.

Our local mechanic thinks the problem might be related to increased back pressure. His reason for this thinking is because previously the engine had a 4" schedule 40 pipe for exhaust and recently we installed a 8" stainless steel pipe from "selkirk metalbestos" due to the 4" pipe corosion issue. The engineers felt the larger diameter pipe would be much easier on the engine. The mechanic felt we should've installed a high temperature fan to help get rid of the exhaust. The TECOCHILL manual stated the back pressure be no more than 26" WC at the highest RPM bet 600*F & 1200*F and 15" WC at the minimum RPM. I would appreciate some further feedback on this issue. Here are the previous measurements taken with the 4" SCH 40 pipe in pdf.

[yellowirenut]

one of these?

http://i435.photobucket.com/albums/qq79/plantkiller_01/stuff/0521091217.jpg

http://i435.photobucket.com/albums/qq79/plantkiller_01/stuff/0521091217b.jpg

did the Tecogen techs replace the engines?
have u talk to tecogen?

[klove]

What's happening to the pushrods, and is that the only issue?

[dweber101]

I would look at the engine heads, ignition timing and valve timing, clearances, etc, and then pre-ignition issues.
Compare Exhaust Gas Temps left bank to right, might be too lean on one side and pre=igniting on the up stroke while the cam lobe still is pushing on the valve the explosion bending the push rod.

Just some thoughts, please tell when you do figure this one out.

Daniel

[Octopus]

You need to have mechanic check the following if he refuses find another mechanic.
1. Are the valve springs weak, ask him what they read when he checks them if theres a weak one replace it.
2. Rocker arm and push rod length check and angular Clarence check for binding in valve train.
3. Valve lash.
4. Engine running rich or lean.
5. Oil pressure.
6. Dial in cam/ find top dead center and check timing
7. Are there metal shavings in oil, put a magnetic oil plug in sump.
8. Rocker arm ratio, flat tappet or roller rockers?
9. Are the push rods turning as they go up and down?
10. Check head gaskets for leaks.
11. Whats the blow by, vac, and EGT?
You could have a bent valve, a wiped out cam lobe, a lifter that isn't pumping up if they are not solid, crappy push rods, lifters sticking, and about 100 other things.
Have the heads been pulled if so correct head gaskets installed?
Did the mechanic pull the valve cover while engine running? It may be messy but you can see whats happening right there and then, they also sell covers with access windows, but I'm old school, we got out rags and kitty litter.
Is it the same cylinder every time?
Which valve bends intake or exhaust or has it been different?
Are there push rod guides?
Is he replacing push rods or just bending them back on a Y block?

[cperk]

OVERSPEED? Anyone? Anyone?

[batterup]

the bigger pipe would mean less back pressure. is this machine engine i should say backfiring thru the carburator sometimes. this would cause push rods to bend backfiring threw exhaust valves. having worked on lots of these machines and knowing engines it is generally from the gas manifold pressure to the intake the gas valve brass stem inside the gas valve wears and lets to much threw. is your engine a 454 or a 350. would be glad to talk to you about this if you would like. assuming top dead center at o degrees and rotor button on number one cylinder ready to fire wear on timing chain was checked yes or no

[coolerinfrederick]

man that is cool, a gas fired engine driven chiller, how many of those are floating around and how would you get any training on a machine like that, i envy you guys

[jim147]

man that is cool, a gas fired engine driven chiller, how many of those are floating around and how would you get any training on a machine like that, i envy you guys

Do you know automotive engines? It may or may not have cast iron pistons but the main difference between your work truck engine and one of these is the fuel.

No reply from the OP but I would look towards the fuel delivery. You can't compress liquid. Something has to give.

jim

[19C]

Hi FireBrick. did you pull the heads? If you did and the heads are still off, look closely at the discharge valve seats and the discharge valve tops. The valve seats look for them beening sunking in and the tops of the valves also sunking in. Seen this problem eat push rods. Good luck.:couch: