Tight timing chain

[DCal]

I'm working on a 400 SBC using a Dart SHP block that has not been align honed, it was checked and is fine. Today I put a rod and piston assembly in to check for clearances, then put the cam in to check it also. I couldn't turn the crank by the snout but I could by grabbing the flywheel flange. There is no runout it's just too tight!! I've never heard of a chain fix for this situation. Got any ideas?

[BigBro74]

Too bad there is no way to mach up the timing set with an electric motor or something and “run it in” awhile to put just a bit of wear on the chain and loosen it up...
You could just try a different chain if you haven’t already.

What kind of timing set is it?

[DCal]

Its a PBM set with an Iwis chain-nice looking set actually.

[BigBro74]

I have not used one of their timing sets in several years......
you may just try a different one and see —for science
I sent you a PM

[Charliesauto]

I'm working on a 400 SBC using a Dart SHP block that has not been align honed, it was checked and is fine. Today I put a rod and piston assembly in to check for clearances, then put the cam in to check it also. I couldn't turn the crank by the snout but I could by grabbing the flywheel flange. There is no runout it's just too tight!! I've never heard of a chain fix for this situation. Got any ideas?

We see this often with the Dart SHP's. Helps if you have several chain sets to try or even using a slightly used chain if all else fails.

[DCal]

I'm working on a 400 SBC using a Dart SHP block that has not been align honed, it was checked and is fine. Today I put a rod and piston assembly in to check for clearances, then put the cam in to check it also. I couldn't turn the crank by the snout but I could by grabbing the flywheel flange. There is no runout it's just too tight!! I've never heard of a chain fix for this situation. Got any ideas?

We see this often with the Dart SHP's. Helps if you have several chain sets to try or even using a slightly used chain if all else fails.

Thanks Charlie, so I'll see my supplier , who I'm sure will let me take several sets home, and then mix and match until I'm happy. Or go to a different brand.

[Kevin Johnson]

https://www.rockler.com/wooden-handscre ... ygQAvD_BwE

Gently radius the contact areas and squeeze the mounted chain from the sides like a dual tensioner. Rotate the chain a bit and repeat. Use your hand to increase loading rather than a monkey wrench. You would just be adding a little more pre-stretch. I know Iwis are supposed to be pre-stretched/tensioned.

Never done this. Do at your own risk.

[DCal]

I'm working on a 400 SBC using a Dart SHP block that has not been align honed, it was checked and is fine. Today I put a rod and piston assembly in to check for clearances, then put the cam in to check it also. I couldn't turn the crank by the snout but I could by grabbing the flywheel flange. There is no runout it's just too tight!! I've never heard of a chain fix for this situation. Got any ideas?

We see this often with the Dart SHP's. Helps if you have several chain sets to try or even using a slightly used chain if all else fails.

Thanks Charlie, so I'll see my supplier , who I'm sure will let me take several sets home, and then mix and match until I'm happy. Or go to a different brand.

Got an update, tried 3 different sets all with the same results. This left the crank sprocket which measures .030 bigger at the bottom of the teeth diameter . Its almost midnight and I can hardly wait for tomorrow morning to tear that gear off. I'll update in case it may help someone else.

[Kevin Johnson]

https://www.rockler.com/wooden-handscre ... ygQAvD_BwE

Gently radius the contact areas and squeeze the mounted chain from the sides like a dual tensioner. Rotate the chain a bit and repeat. Use your hand to increase loading rather than a monkey wrench. You would just be adding a little more pre-stretch. I know Iwis are supposed to be pre-stretched/tensioned.

Never done this. Do at your own risk.

I know we've been over this many times but I had to laugh:

By the way, Kevin Cradduck, my partner, and the guy who runs NitroPlate, is a patent holding timing chain engineer. He'll tell you in a heart beat that chains do not stretch, the gears wear. If you ever saw what they use to pre-stretch a timing chain, you'd be pretty convinced that your engine simply won't stretch a chain.

So, you don't "stretch" a chain because the colloquial meaning of that is chain/gear wear. You "pre-stretch" a chain as does a patent holding timing chain engineer. Glad to clear that up.

Chain pre-stretching machine.jpg

[BigBlocksOnTop2]

Pitch diameter of your cam gear has screwed up some good progress. It's always something....

[DCal]

We see this often with the Dart SHP's. Helps if you have several chain sets to try or even using a slightly used chain if all else fails.

Thanks Charlie, so I'll see my supplier , who I'm sure will let me take several sets home, and then mix and match until I'm happy. Or go to a different brand.

Got an update, tried 3 different sets all with the same results. This left the crank sprocket which measures .030 bigger at the bottom of the teeth diameter . Its almost midnight and I can hardly wait for tomorrow morning to tear that gear off. I'll update in case it may help someone else.

Sometimes I just piss myself off, the sprockets are the same once I got the gear off where I could properly measure them. Called Chris Straub and have Rollmaster set on the way. I'm praying that this fixes the problem.

[Kevin Johnson]

Thanks Charlie, so I'll see my supplier , who I'm sure will let me take several sets home, and then mix and match until I'm happy. Or go to a different brand.

Got an update, tried 3 different sets all with the same results. This left the crank sprocket which measures .030 bigger at the bottom of the teeth diameter . Its almost midnight and I can hardly wait for tomorrow morning to tear that gear off. I'll update in case it may help someone else.

Sometimes I just piss myself off, the sprockets are the same once I got the gear off where I could properly measure them. Called Chris Straub and have Rollmaster set on the way. I'm praying that this fixes the problem.

Just a thought. Making the assumption of trust in your initial measurement in situ suggests that the interference fit on the snout is too great and is causing the gear to radially expand. (Perhaps the snout has a taper that increases in diameter in the region of the keyway.)

When you remove the gear and they all then match in root diameter suggests consistency in their manufacture, which is good.

Good luck.

[piston guy]

Dave ,
I had a friend with a 289 Cobra that had his engine rebuilt and couldn't get more than 50 miles out of it before it lost oil pressure. First builder took it apart , found bad cam bearings , replaced them and engine had oil pressure for another 50 miles . Goes to a big time Chevy super stock engine builder and same thing twice. Comes to me in desperation. I find the WAY tight timing chain. Being curious I try a new top gear , same new crank gear same, new chain on his original gears same. I ended up having to use an "experienced" chain to get some "play" in the chain like normal. put it back together with another set of cam bearings and now 9 years and a few thousand miles ( including a few vintage races) it is still going strong.
Hope yours is less trouble.

[DCal]

Got an update, tried 3 different sets all with the same results. This left the crank sprocket which measures .030 bigger at the bottom of the teeth diameter . Its almost midnight and I can hardly wait for tomorrow morning to tear that gear off. I'll update in case it may help someone else.

Sometimes I just piss myself off, the sprockets are the same once I got the gear off where I could properly measure them. Called Chris Straub and have Rollmaster set on the way. I'm praying that this fixes the problem.

Just a thought. Making the assumption of trust in your initial measurement in situ suggests that the interference fit on the snout is too great and is causing the gear to radially expand. (Perhaps the snout has a taper that increases in diameter in the region of the keyway.)

When you remove the gear and they all then match in root diameter suggests consistency in their manufacture, which is good.

Good luck.

Kevin I have to take the blame for the measurement error, I even put the sprockets on the gram scale and they and the other components were virtually identical-their machine work was great-it just don't fit!! When the other brand gets here it will tell me a lot and I don't want to bash anyone publicly. Thanks for your ideas and I have the chain stretcher machine in the back of my head just in case.

[Old School]

Sounds like you have found your problem. I have experienced the cam gear being as much as .030 in front of the crank gear. That will cause binding also. I machined the necessary amount off the cam gear behind the bearing so they were parallel with a straight edge placed on top of the crank snout. I found that on 3 sets from the same manufacturer all made about the same time. Get the gears in alignment and no more tightness or binding.