Indexing flywheel

**Jay Smith** · 10-03-2018, 08:52 AM

I agree �� I was just saying 99 % of all these conformation of timing are going to be done with heads on , I’ve been building these black motors for 25 years 2 to 3 a week every week .. Always different ways to skin cats all “ways/methods” are welcome here , the end successful results should be the main thing desired .
Peace ,
Jay

**FORBESAUTO** · 10-03-2018, 09:39 AM

Completely understood, and agree. Just didn’t want any hard feelings with one the guys I look at as one the greats, and someone I have utmost respect in. Last thing I want. Keep up the good work!

**FMP** · 10-03-2018, 09:54 AM

Originally Posted by Glasstream15

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

How far off is the spacing on an inline? Would think twist might become an issue over time.

**Chaz** · 10-04-2018, 01:07 PM

Originally Posted by FMP

How far off is the spacing on an inline? Would think twist might become an issue over time.

Twist is usually a function of RPM ..

Torsional rigidity ( like that one lol ) will tend to bring it back to where it was.

I can't speak about or blame an inline or 2.5L, but I have checked the index of a 3.0L crank. While far from perfect, they are not near bad enough to see 2*-3* difference in piston location per crank angle on their own.
The blocks are the main culprit. One would think over time that as machines got better the parts that they produce would have gotten better.

Instead, it seems the factory has used the technology to make parts cheaper and faster.
I know this thread is about roll it up, roll it down, make a mark , move on. For those that want to think it thru a little deeper as to why you would have to settle for some cylinders timed at 21-22-23 while the others are at 25. And yes it's better that than burning one up.
Nearly 50 years ago some class killers / automotive machinists figured out that they needed to come up with a way to deal with core shift and tolerance stacking once and for all and develop a "set standard" that everyone could bring their parts up to if they choose to. It would be rare today to go into a shop that builds big power and not find an assortment of BHJ fixturing equipment.
Since I weld a lot of blocks I made up a couple of "solid bar crankshafts" to bolt between the block and front half. Pretty amazing to do a drop down measurement in the 4 corners to see how twisted even a "cherry" block is ... They speak of timing issues in the text below .

http://www.bhjproducts.com/bhj_conte.../bt1_intro.php

Another area they are pretty bad is bore centers and being 90* to the crank centerline. Ooppsss lunch bell just rang ...

http://www.bhjproducts.com/bhj_conte...ntfixt/btk.php

**FMP** · 10-04-2018, 02:14 PM

All part of the perfect world we live in

**KIRCHNER** · 10-04-2018, 06:00 PM

i think merc should invest in a new crankshaft machine, 4-5 ' off is ridiculous. i cant believe what im hearing. bet those jap motors are rite on the money!

**gmacrae** · 10-04-2018, 06:13 PM

Originally Posted by KIRCHNER

i think merc should invest in a new crankshaft machine, 4-5 ' off is ridiculous. i cant believe what im hearing. bet those jap motors are rite on the money!

I find it hard to believe the cranks could be manufactured so far out of wack accidentally. Looking at mine it seems deliberate. 1,2,3 are perfectly spaced 60 degrees apart, then there's only 55 degrees to #4, then 60 to #5 and 60 to #6. Then 65 back to 1. Like merc decided the engine would balance better with 5* less between the middle 2 or something.

I can imagine there being a common variance in triggers and switchboxes though. (esp if they're made in the US... I joke I joke!

)

Just theorizing here so don't mind me - would love to know if anyone knows why my motor isn't spaced 60* evenly all the way round.

**FMP** · 10-04-2018, 06:19 PM

As mentioned above a variety of reasons can contribute to the results. Maybe they did finish the crank just so. If you measure the crank out of the block, a crank shop can tell you exactly what you have I would think.
How's the 135 and 246 spacing? As it pertains to ign advance.

**gfinch** · 10-04-2018, 06:35 PM

Chaz thank you for this information and the BJH site.

**LakeFever** · 10-05-2018, 07:21 AM

No doubt mass production has its flaws. There is always a service spec for tooling and good techs stay on top of this without pressure from management and bad techs dont. Then theres the Monday/Friday builds. All a bit of a crap shoot really. I am always looking at odds vs gains and err on the side of caution but Im not racing boats, in which case Id be looking at every angle for that little extra edge. For a lake rocket I want to be able to get back to the launch as often as possible under my own power so a little less power = a lot more win for that goal. Great thread, very informative thanks for the info S&F!!

**TEXAS20225** · 10-05-2018, 02:20 PM

i agree with jay i have one of his so long i dont member when i got it it was years and years maybe even more years but at 73 everyday seems like Sunday

**FORBESAUTO** · 10-05-2018, 04:02 PM

Ok, just reread my original post and discovered why some of the confusion. In my mind I put all this info in and somehow my fingertips just didn’t do it. Thought I explained how to find TDC using both methods, a piston stop and dial indicator, even mentioned both steps in text just left one out

. To clear it up and hopefully make it easier to understand proper way of finding true TDC. 90% of the time when I’m indexing a flywheel its during an engine build, I prefer doing it before putting heads on using a piston stop. If heads are on you can use either a stop threaded in plug hole or the dial inicator like Jay sells. The principal is the same. The idea is to get a reading on flyweel with the piston at the exact distance both just before TDC and just after TDC. The point dead nuts between these two points is perfect TDC. So when using a dial indicator instead of a solid piston stop, you bring the piston to its upmost travel on dial (piston will stay at this point for small amount of rotation without moving, thus the reason for the method I’m speaking of), adjust this point to zero on your dial, now turn crank clockwise until piston is let’s say .010 in hole, note where pointer is at on flywheel. Now turn crank counterclockwise until piston is .010 in hole, note where pointer is at on flywheel. If pointer is set to perfect TDC the two points will be the exact same amount of degrees from the TDC mark, one ATDC and the other at BTDC. If not move pointer accordingly until you do the steps and they are. (If on a lightweight flywheel without degree marks TDC Mark should fall the exact same distance from the two marks noted. Hope this make it easier to understand the idea behind the process.

**dwilfong** · 10-05-2018, 07:01 PM

https://www.facebook.com/brett.croxs...405516978/?t=3

**FORBESAUTO** · 10-05-2018, 07:06 PM

Also just for clarity. The TDC procedure is only done on cylinder 1 to make sure your pointer is perfectly set to the flywheels factory TDC Mark. This is important for future reasons in case you pointer get moved you can always put it back and the marks you made on flywheel using the pointer for all the other cylinders will always be accurate. Alter pointer is set, all you have to do is measure desired distance piston down from upmost point of travel in cylinder BTDC for max ignition timing you want to run (.150 for 25 BTDC) and place a mark on flywheel where the pointer meets.