So I just replace the upper timing chain on the 18 RC engine,

Put it through the upper tensioner and cam shaft sprocket and the crank shaft sprocket.

Tightened all the bolts and gave the entire timing chain, upper and lower, a quick test by cranking the sprocket bolt on the crank shaft with a 19 mm BOX on a ratchet.

So everything is moving. It seems that the chains are fine.

But then there seems to be a jump that coincides with a compression stroke.

Looking down the head ( the valve cover is still off ), I can see the upper tensioner extend and retract at various times in the turning of the gears. It's like the upper chain goes loose and then tight. The tensioner expands its arm and then retracts its arm. It all happens in a set sequence.

The lower chain seems fine. No jumping, though one side ( the driver side ) seems slack.

Is this how an upper tensioner operates? Or is the tension suppose to be continuous with the arm always extended?

Is the tensioner damaged? Is the chain the problem with a link binding?

Or is everything as it should be?

I'll crank it again tomorrow with just the starter. I'll remove all the plugs so there isn't any compression. Then turn the ignition a few time and let the starter turn the timing gears. I'll listen and see.

Any thoughts?

 

Today I cranked the engine. I took out the spark plugs, so there won't be any compression on any of the cylinders nor any spark to combust. Just the starter turning the crank, cam, gears, etc.

I did this a few times. The upper chain still seemed loose. Too much slack. Did it a few more times. Same result. Too much slack.. Did it again.

This time all chains were snug and firm. It seemed like the correct tension!

Is this normal and expected after replacing a timing chain. First all chains are slack, but then te chains start to firm and tighten with the engine being cranked and turned? Or is it an anomaly, and the chains might return to the slacken/loose phase?



'll crank it again later and see if anything has changed from tight to loose....or maybe it stays tight.

Thoughts and perspectives please.

 

Man wish I could help ya out but in my experience with other engines this doesnt seem correct. However with no compression it might be the fact when your valves release there is no pressure keeping it taught therefore it seems like its slipping or skipping when its just releasing as if the cylinder was dead or something

 

I also think it was not correct. The chain should have and even tightness. And it does now.

I'm wondering if the tensioner needs a bit of working itself in, kind of like a pair of shoes. Stiff and unyielding, but then after a bit of wear, they fit just right.

BTW, whose pic on the avatar?

 

Yah tensioners can be tricky business, i think I would put it all back together and slap a timing light on that thing and see whats going on. If anything changes drastically and how it runs.

Avatar pic is Lupe Fuentes, she is my wifes cousin 2x removed or something like that I just know when I seen her at a family reunion I was like WTF! Yah my wife knows I have the pic hahahah

 

So I was going to put the timing chain cover back on, but then I stated thinking about the upper timing chain. People were telling just run the engine, and if the chain is loose and breaks or whatever, then just replace it. I even agreed with that reasoning.

But then I started looking at the chain again. On one stroke at TDC, the side away from the tensioner goes limp and loose at the bottom gear. See the pics.

It just seems wrong.

I spoke with some guys at the autoparts store. They didn't know. I was told it was normal to have one side loose with belt-driven timing, and the side away from the tension being loose is consistent a belt-driven system. But this was a chain driven timing, so no one was sure.

Rather than chance it, I spent a whopping $10.99 for a new chain. I'll replace it with a new chain. This way if the chain is still loose, I'll know it was not a faulty chain. $11 is worth the peace of mind via process of elimination of problems and future hassles.

 

Ok so looking at the side that is loose, if you follow that chain up to cam gear is there a tensioner once you get towards the top of the side of the chain?? If so what side of the tensioner is the chain on?? It kinda looks to me like when its spinning back up if there was a tensioner the chain went onto the inside of it might be able to pull that chain back towards crankshaft gear on its way to the cam gear.