Engine experts/geeks: Intermediate Shaft Outer Measurement ok?

Fritter · 10-08-2008, 10:00 AM

Spec is 24.980 to 25.000. Mine measured in at 24.9682. No wear limit is given, but the crank wear limits are .011 below the lower spec, which would be 24.969 in this case, so I am thinking I may squeak by. Of course, I will use brand new bearings here also.

This is for a basically stock '68 2.0 with Solex cams and JE 9.5 pistons, not a super duper hi po motor.

Thanks for any opinions!

304065 · 10-08-2008, 10:06 AM

Mike, the specification range is typically intended for new parts, and if a wear limit is important, the factory specifies one. The diameter measurement with a pair of 4,5mm pin gages in place is basically intended to tell you how much the teeth have worn. That is, if the teeth are dimensionally smaller then the pins ride closer to the shaft axis and the overall diameter is smaller.

I would go ahead and assemble, but be absolutely certain that the backlash measurement is in spec before you close the case. It's kind of hard to set up for this measurement, see my threads on the subject, but if the gears are worn then there will be too much slop which will be noisy and could lead to the timing being jumpy.

Fritter · 10-08-2008, 10:14 AM

John, this is the not for the gear or shaft movement backlash, it's for the shaft/bore spec on the rear bearing. First thing's first!!

Thanks.

304065 · 10-08-2008, 10:23 AM

Duh, I should have realize that 25mm is around an inch not four. Anyway, what you are saying is your intermediate shaft is worn below the lower limit for installation of a new part.

Your '68 case has bearings? OK, that makes it a "Version II" with a thrust bearing but no plain bearing? I have the same answer, if there's too much slop the timing will walk around. Can you measure the clearance with plastigage?

Fritter · 10-08-2008, 11:15 AM

Yes, it's a late '68 mag case with no bearing on the inner shaft. Yes, I will have to plastigauge it. My crank measures within spec and is in great shape, so I'll put the crank, intermediate shaft, and old bearings in with plastigauge dry and torque it up and then take it apart and see what magic I get.

304065 · 10-08-2008, 12:02 PM

Be careful of the perimeter bolts when you torque it, over the years DPOs try to fix oil leaks by overtightening the M8 studs and when you torque them down. . . "POP" But it shouldn't take long to measure the clearnance and see what's up.

Worst case you get a late shaft and have the case modified by Ollies (now in Lake Havasu!)

Nine9six · Nine9six's Garage

Mike,
You are correct in your logic...
You are below spec .000433 " on a diameter requirement of .984251 "
Which is approx .2273% of your diameter. = no problem.

304065 · 10-08-2008, 02:45 PM

I don't follow the math.

Metric conversion:

High limit 25.000mm / 25.4= .984252"
Low limit 24.980mm / 25.4 =.983465"
Your part 24.9682mm / 25.4 = .983000"

So your part is 0.0118mm below the low limit or .000465", which is .047% of the low limit diameter.

For the crank:
High limit 56.990 or 2.243701
Low limit 56.971 or 2.242953
Wear limit 56.960 or 2.242520

The wear limit is .011mm below the low limit, or .019% of the low diameter.

So your IS is worn about two and a half times more than the equivalent percentage that the wear limit is below the low limit of the crank. If the same percentage applied on the IS, the wear limit would be 24.975mm.

Fritter · 10-08-2008, 04:03 PM

Nine9six, I don't know where you got the .2273%?

Cool and good math John.

The clearance spec is .030 to .084mm, or a .054mm spread. High end of clearance is .012mm over the mains, or about what my difference is from low limit to my measurement.

Let's hope my .001 to .003" plastigauge will crush, because anything over .0762mm (.003") will not crush the green plastigauge.

Fritter · 10-08-2008, 10:04 PM

Well, I plastigauged (is that a word) both my mains on the crank and the two intermediate shaft bearings. All were smack dab in the middle of the spec except the problem rearmost intermediate thrust bearing, which was at the top end of the spec (.084mm) with the old grungy bearing (which is pocked and actually missing some chunks).

The front intermediate shaft bearing is known to take some wear, from the chain tension.

So, I think with new bearings I'm good to go, and I also can run with my front "bare mag" intermediate shaft bearing surface, as the clearance there was .051mm, in spec.

Long live the mighty 2.0 motor!!