When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
My 1995 Carrera 2 Engine was taken apart and all gaskets and seals were replaced. The o-rings on the old lifters were also found to be falling apart so we replaced all of them with new ones.
The first time the engine was reassembled, the timing was off the engine was running very rough. After realizing I needed the specialty cam timing tools for the job, we set the proper timing and started up the engine.
Now when I start the engine, I hear a knocking (clunking noise) from the left side valve covers (more pronounced from lower cover). I'm trying to diagnose what the possible cause could be. It almost sounds like what a engine sounds like when it has bent valves. Is it possible I bent the valves when the timing was incorrectly set?
I also have been reading up on this forum and it also seems like bad lifters or the lifters not pressurizing. Any suggestions on what to tackle first?
The entire lifters were replaced and they came with new O-Rings. I pulled out the rockers and the surface on the exhaust side rockers isn't as smooth and shows some marks. Possibly from the incorrectly set timing before?
Do they look so bad that they need to be replaced?
I would look at the lifters,and make sure one wasn't quite seated right and got damaged on initial start up. I am assuming that all of your rockers were numbered so they went back in the exact order they came off.
The rockers look ok in the pictures (looking on my cell phone)
Someone else mentioned a lifter not well seated, that could be.
I would start it and bring it up to temperature. If you can determine which side is making the nose, start there. Remove the rocket covers and check to e if any are really loose. If you find one, pull it and inspect the lifter. If all is good, nose to the upper or lower, whichever you didn't open and check yet.
If you have an inspection camera you could also look at the valves to see if there is damage.
Your rockers should have a profile curvature that is the same throughout the radius; if you can feel a flat, or a discernible change in the existing profile, I'd say there was some interference going on, and more investigation is needed prior to any further running or even thinking about bringing the car up to temp.
While it's difficult to imagine the car running at all, let alone roughly, while being out of time enough, for the pistons to smack the valves; I'll need to defer to those more knowledgable in the specifics of Porsche 993 timing and if that possibility even exists.
After I replaced the lifters in my car it sounded terrible on the first start up. They take some time to pump up and quiet down. There was a small instruction sheet included with mine (Ina brand) that describes a bleed procedure. The content suggests it may take repeated attempts holding revs and idling to get the air out.
I had a tick after that wouldn't go away and I later found a single new lifter that never pumped up (plunger was stuck). It's possible to get a bad one right out of the box.
Running it with the timing off can do some damage though, as suggested above a leak down is in order to make sure nothing's bent.
Do 993s have timing chain tensioners like the 964? Maybe you installed one upside down? Take the cap off and make sure the nipple w/ pinhole is pointing toward the cap.
Need more data and diagnostics. These engines are interference engines which means you can have the pistons and valves collide if you do not set the timing correctly.
There is a lot of knowledge on this forum, but you need to supply more information, the more info the better our guesses. An example would be is how far was the engine torn down?
Anyways, it sure sounds like the timing was set wrong and you smacked a piston with a valve - how far out was the timing when you started the car vs the reset timing?
BTW, you can set the timing the old fashioned way measuring lift at TDC, but that is not your worry right now.
You need to check if you have a bent valve - leakdown (as mentioned before) is a good diagnostic. Do not run the engine anymore, figure out what is wrong first and fix it - which may require stripping the engine down to at least removing the heads. You might be lucky too and its something else, like your lifters are taking time to pressurize. That is why the question on how far out do you think the timing was?
Based on a visual inspection of the valves, they're not bent. I also had another Porsche specialist come take a look at the rockers and they seem fine.
It may be a possibility that the rockers were not put back in the same position as they were taken out from. I will confirm with my mechanic tomorrow. I always suspected the lifters not pressurizing as well. Whats the best way to diagnose this? Based on my searches it seems many people run into a bad lifter or two even with a brand new set.
04-01-2015, 07:48 AM
Help diagnosing noise in engine after reassembly
