Indexing flywheel

[FORBESAUTO]

There has been a lot of confusion about indexing flywheels and is a term a lot of us use, but never really explained. I would like to share my method of doing it, hopefully it will help some understand the method. So here's my simple but accurate way of doing it.
1st step is to get pointer set dead nuts to TDC on cylinder one TDC mark on flywheel before making any marks on flywheel. I feel the best method is to use a piston stop. I normally do it while I'm building the engine, but can be done through spark plug hole also. I use a homemade adjustable stop. The idea is stop the piston before it reaches TDC, doesn't really matter how much, I like around 5 degrees are so for ease of measuring. Turn engine clockwise until stops on piston stop and degrees at pointer, let's say we read 5 degrees btdc. Now turn counter clockwise until stops on piston stop and read pointer. Let's say you read 6 degrees atdc. This means your pointer is off 1/2 degree. Adjust your pointer 1/2 degree towards the smaller reading and do process all over again until your readings are exactly the same in both directions and your pointer is set to perfect TDC.


Next step is to mark every cylinder to your desired max timing. This is normally 25 btdc on the V6 merc, which is 0.150 of the piston reaching TDC. Set up a dial indicator to center of piston, bring piston up to maximum travel were indicator is at its maximum point before begins going back down and zero your indicator at that point. Turn engine counterclockwise until piston travels downward to 0.150. At this point you place a mark at point where pointer is pointing at flywheel. Repeat this process on all six cylinders to mark 25 btdc for each cylinder. I only bother marking the 25 degree mark on the cylinders being that's the only reading I care about for the other 5 cylinders. If you want to mark degrees other than 25 you will need to do some figuring on how many thousands in the hole you need to mark. You can do this by setting up a degree wheel a take measurements. (X amount of thousands does not equal x amount of degrees. The amount the piston travels in one degree increases the farther it is away from TDC and BDC due to the angle of the rod.) Again I normally do this while head is off, but Jay Smith offers a TDC gauge ( dial indicator set up through spark plug hole to read piston travel.
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Hope this is helpful and makes since.

[Glasstream15]

And that JRSE dial indicator is a HANDY gadget, especially on my InLine.

[gmacrae]

Hey Forbesauto cheers for the tips... I recently indexed my flywheel by measuring around the flywheel with a measuring tape (706mm), diving that number by 6, and then marking each step around in those 117.6mm increments. This guaranteed that I'd get accurate marks of 60 degrees each but it seems 4, 5 and 6 TDC's don't quite match up! Each one is about 5 degrees out. 1, 2 and 3 are perfect, then there appears to be a few degrees difference to 4... It showed up when I was checking ign timing on each, so I checked each TDC with something down each hole and confirmed it.

Are you aware of the crank in these motors not actually being separated by 60 degrees between all 6? This is where your dial indicator method would prove best of course!

[FORBESAUTO]

I have heard others insinuate that before, being the reason 2 and 5 are the “hot cylinders”. I can tell ya on most engines cylinder 6 is the one I have to set the 25 degrees ignition timing to, because is usually the one runnin a tad bit higher than the rest. Also Unfortunately every time I’ve turned 6 into molten ‘luminum, it’s been because of ignition timing

[LakeFever]

I have heard others insinuate that before, being the reason 2 and 5 are the “hot cylinders”. I can tell ya on most engines cylinder 6 is the one I have to set the 25 degrees ignition timing to, because is usually the one runnin a tad bit higher than the rest. Also Unfortunately every time I’ve turned 6 into molten ‘luminum, it’s been because of ignition timing

Gold!!!!! Pure gold pony boy!

This is the kind of info that keeps us keeping on thank you Forbes again for the data

[Jay Smith]

Gee that text looks familiar in fact it’s a copy of the instructions I supply with every JSRE TDC indicator tool I sell That’s the reason EVERY motor I build will have 7 marks on the flywheel , dial indication marks to check spark location per every cylinder ...
Jay @ JSRE
$ 75.00 + Freight for tool and easy to follow instructions , we sell a zillion of them

[FORBESAUTO]

Great minds think alike

[Jay Smith]

Been doing them like that for 25 years ��

[gmacrae]

So has anyone else noticed that 4, 5, and 6 crank journals aren't spaced within 60 degree intervals of #1 TDC? (ie. there's only about 55 degrees between 3 and 4) or is my motor some kinda twisted abomination?

[nitro_rat]

So has anyone else noticed that 4, 5, and 6 crank journals aren't spaced within 60 degree intervals of #1 TDC? (ie. there's only about 55 degrees between 3 and 4) or is my motor some kinda twisted abomination?

It’s normal. That’s why you check the timing on all 6. Set your timing so that the most advanced cylinder is at 25* (or whatever your target number is).

[Merc 2.5]

I've never done this indexing but b4 I put heads on this new motor ,I'm gonna give this a try , forbes you may have to help .e thru this if I start questioning myself , I'm gonna keep it at 23 but I wanna try keep em all same and I dnt want a 26 27 or a 30 sumwhere

[nitro_rat]

I wanna try keep em all same and I dnt want a 26 27 or a 30 sumwhere

The point is due to the throws on the crank not being ground perfectly 60 degrees apart you won’t be able to get them all the same! You can’t eliminate the variance but you can control on which side it occurs. It’s better to have a 20, 21, 22 somewhere than a 26, 27 or 30!

[FORBESAUTO]

No problem, I’ll help in any way I can. If ya not 100% clear feel free to contact me directly, if it’s easier.

[Jay Smith]

Install your heads buy a JSRE dial indicator that screws in your plug holes why complicate your life . Soooo much easier . My 2 cts..

Comes with complete and easy to understand instructions ..
Jay @ JSRE 832 597 2603

[FORBESAUTO]

Or if ya heads are already on, you can use a JSRE TDC gauge as I stated in post 1. I’ve always promoted Jay Smith and his ability, not really sure what this is about, but anyhoo. Coming from 20+ years in the Automotive field degreeing in camshafts, I have just come to prefer using the piston stop method finding true TDC. I gave examples using both methods, so anyone can use the method they prefer and feel most comfortable with