Hung up on 912 motor rebuild

[Igofastr]

Howdy all,

I've got a question for those of you familiar with 912/356 motors. I'm in the process of putting a 912 engine together from spare parts I've had laying around, and have run into a problem. After putting on the heads, rockers, etc, I can't seem to get enough adjustment to allow the valves to completely close. It's as if the pushrods are too long.

Now I'm no expert, but I've built a few 912's over the years (been a while), but I just can't see where the problem is. Of course, there are a number of possibilities, as I'm using parts not originally from the same motor, but I'm still somewhat perplexed. Here are the possibilities. The cam is an unknown grind, but seemed fairly agressive when I took measurements. I called around, and nobody could identify it. But, it must have worked sometime, because it would have come out of an engine that I bought for spares. The only way it could be a problem is if the base circle is too big. I don't recall this being an issue when I took measurements years ago.

The case...could it have been line-bored and then shaved? I suppose, but that would have been one heck of a shave to bring the heads so close that I can't adjust the valves to close.

The heads, they were rebuilt by Ollie's, and don't look to have been really beaten on in the past. Could they have been flycut, etc multiple times in the past? Possibly, but again, enough to take away all my valve adjustment?

Pushrods...took 'em out and checked them against a second set...seem to be standard length. And yes, they were seated in the lifters.

Cylinders, standard big bores (reconditioned by me), thin shims (gonna mosty be a track motor, I'll take care with the increased compression).

I suppose the cumulative effect of non-standard components could be the problem, but I'd like to check easy/obvious things first, before I resort to a complete teardown of a newly assembled motor.

Anyone have any ideas where to start? Anyone know what the measurement from one head to the other typically is (so I can see if mine are closer than they should be)?

Thanks, Ron

[maybe368]

You are missing the washers under the head nuts, you need to loosen everything so nothing breaks. Each head nut should have a hardened washer under it, ask me how I know...Mark

[Igofastr]

Originally Posted by maybe368

You are missing the washers under the head nuts, you need to loosen everything so nothing breaks. Each head nut should have a hardened washer under it, ask me how I know...Mark

Good thing to check. I think that they're there, but I assembled that part 6 mos ago, so I can't remember for sure. I'll pull the heads tonight, and report.

Thanks, I really appreciate the input.

[maybe368]

If you search head nut washers over at the 912bbs.org I put the depth measurements down the stud holes, both with and without the washers, because my eyes could not tell if they were there or not. I used the depth side of calipers to measure. Did your headnut o rings want to slip out when you torqued them? Mark

[maybe368]

here are those numbers...


All measurements are from the stepped down washer cutout and are plus or minus .2 mms.

The 2 inner, upper ones are 18 mms without washer and 16 mms with.
The 2 outer uppers are 53 without and 51 with.
All 4 lower are 55 mms without and 53 mms with.


Mark

[C. Clark]

If you do need shorter push rods.....https://www.classicandspeedparts.com/index.php?page=shop.product_details&flypage=flypage.tpl&product_id=149&category_id=182&keyword=push+rod&option=com_virtuemart&Itemid=53

has them, just a thought.
Chas.
356912911

[Igofastr]

Originally Posted by maybe368

You are missing the washers under the head nuts, you need to loosen everything so nothing breaks. Each head nut should have a hardened washer under it, ask me how I know...Mark

Mark,

You nailed it!

Pulled the heads last night. Somehow, I used the special washers on the 4 upper bolts, but not under the ones that hold the rockerstands.

DUH!!

Luckily, and easy fix.

Thanks, Ron

[maybe368]

I have a blue 912 manual that says that the only ones with washers are the upper ones. When I read it your post, it was like deja vu all over again. Glad it worked out, you'll be driving soon, let me know how it runs...Mark

[912UK]

classic trip up this one...

Glad you had no damage on the heads as well