So I just purchased a 1991 DB51T which was missing on one cylinder due to a bad plug. Got that fixed asap. It drove and sounded great when driving it home from the shop (about 7 miles or so). I topped up the gas with 93 octane and parked it overnight. The next day I drove it down to the store and noticed a loud knocking that seemed to come from the very front of the vehicle at idle. Nothing to be done right then but to shop and get back home (about 1.5 miles each way @ 35mph tops). Checked the oil level and it is full, smells pretty gassy though, and is black. It only does this at idle when warmed up.Waited for it cool down a bit and fired it up again and there was no knocking. It is a pretty loud knocking sound. I just went out and let it run up to temp and then gave it a bit more gas to heat it up more and see if I could replicate the issue but it did not come back. It seems to happen only after driving it a bit at a decent speed. My working theory is that the oil is older than heck (if I am reading the service tag right it was last changed in 2007) and loses viscosity when hot. The shop mentioned that my cap and rotor are also in very corroded and need replacing asap. I have ordered up a cap, rotor, wires, oil, air, and fuel filter for when I change the oil in hopes of that solving the knocking. Do you guys think I am on the right track with my thoughts on the knocking issue? There are only 10k miles on the rig so I would be a bit surprised it there was a major issue in the engine. I am expecting to deal with more exposed components that have bearings and bushings to fail from likely sitting quite a bit. Although the shaken only just expired I have purchased a few vehicles that sat more than they should and know what to expect in the next year or two. Edit: It is more of a tapping noise I think after a quick drive around the neighborhood. Like a quick clack clack clack.
With a dead plug on a carburated engine, you should NOT be driving it without an oil change. Gasoline is a solvent that washes oil away. Change the oil with some fresh 5w30 or 10w30. adjust the valves and then give it a test.. FWIW, the filter is not special. USDM Suzuki cars use the same filter as well as Toyota 4cyl and even many lawn tractors.. The common fram number is PH4967 but ordering for a 1998 Corolla is what I always do
Thanks matt167! I was running through my head what it could be and was also thinking that running it on a dead plug likely caused some gasoline to get mixed in the oil thus making it less viscous. I have no idea how much it was driven before I purchased it but know that I did test drive it about 4 miles (half on the freeway!!!) before I decided to put my offer to buy forward. I drove it right to a shop to get the plug issue fixed as I did not want to slag my catalytic converter on the way home before I could fix the miss. It is not as bad today as it is pretty dang cold here this weekend. I guess that I will be keeping "Major Domo" the mini monster truck parked until I get my tune up supplies in the next week or so. And yes I could go grab the oil filter today but the temperature drop from thursday (65F) to today (39F) was faster than my blood can thicken up. I will wait a spell and acclimatize a bit before crawling around on the ground to change my oil.
rent a big pipe cutter for the old oil filter when you do. If you ran it that long with a miss/ gas in the oil. It could have wiped a bearing
I going to keep my fingers crossed and hope it was just the oil thinning out due to gas seeping in from the missing making the valves get noisy when at operating temps. I will definitely be dissecting the filter after I change the oil.
You might also take a look to see if the bolt head holding the crankshaft pulley is still there. Kind of rare, but it has happened in the past and if missing will allow the pulley to 'walk' back and forth on the shaft. Fred
If its a slower knock its from the bottom end and may need bearings. If its a faster tick tick tick its most likely from the valve train. May need a valve adjustment if thats the case.
I haven' t gotten around to doing anything about it yet as it has been pretty cold here. Seems like it could be the valves. Having never sat directly over a motor with little to no noise isolation it is tough. Lol. These rigs are so awesomely basic even compared to Isuzu NPR or Hino type trucks that my spoiled self is having a tough time identifying it if it is even coming from the motor. To me it seems to come from the front past the motor area. Super intermittant though so that makes it even tougher.
