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Re: Why don't our engines have cam bearings?
Posted by: jjohnsonjo ()
Date: January 11, 2020 10:59AM

Wagon Master Wrote:
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Although I torque the block to spec. and check the crank mains at the same time.[/size]


Yeah, me too, but my cam journals looked fine and he seems to have a concern. It would be a shame to put hours of time and money into the studs only to find out later that the cam is to loose.


On my last build my crank kept locking up on the final pull, yes I did the hammer thing. It was the bearing nearest the flywheel. Had it apart at least ten times trying to find the problem, started doing it without the cam. Finally I convinced Clarks it was the bearing shell and they sent me another from a broken up set. That corrected it.

J.O.

65 Corsa Turbo Vert
79 Honda XL 500S
69 Honda CL 160 D
2010 BMW F 650 GS
2003 Bounder 36D
2013 KIA Optima SX turbo-AKA ZIPPY (wife,s car)
69 Newport Holiday Sailboat
Baja 150 dune buggy cart
Coleman HS 500 UTV
2016 KIA Sorento SXL Turbo

Bethlehem,Pa


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Re: Why don't our engines have cam bearings?
Posted by: 66vairman ()
Date: January 11, 2020 06:09PM

jjohnsonjo Wrote:
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> Even with the studs and crank out you can plastic gauge the cam journals. Maybe 20 minutes or so to put it together and torque the the block studs, probably don't even need a full pull. If clearances are good, that is one more thing off your mind so you can focus on the rest of your build.

Agreed - that's what I do and usually the bearing surfaces are within spec. If not in spec., then the block goes to the scrap metal place. If the bearing surfaces are corroded then you may want to look for another block.

BTW - Aluminum is an good bearing material and the Pontiac OHC six ran the cam in the aluminum head without issue. Also note that since the Corvair cam is installed when the block is apart the journal diameter can be smaller vs. an end load cam were the journal size must be large enough to allow the cam lobes to pass. This means the Corvair can have more block material around the cam journals.

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Re: Why don't our engines have cam bearings?
Posted by: 63 Spyder Ragtop ()
Date: January 11, 2020 06:23PM

Thanks, 66vairman.

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Re: Why don't our engines have cam bearings?
Posted by: cnicol ()
Date: January 11, 2020 06:46PM

Joel wrote: Align boring a block would take material off the mating surfaces of the cases and then cut the cam bores back to stock size or at least that's how mains on regular engines are done. No oversize cam needed."

Craig replies: I'm no machinist but in my understanding you can't do it as described above because machining the case mating surfaces affects the fit of the bell housing, top cover, and rear housing. In prior discussions, I believe the analysis was that you had to bolt and torque the cases then bore the cam holes oversize; necessitating use of a (non-existent) oversize cam.

Craig N. Coeur d'Alene ID.
66 Black Monza 4dr, 4.2L V8 49k
61 Seamist Jade Rampside 140 PG
60 Monza coupe (sold, sniff sniff)
66 Sprint Corsa convt - First car! Re-purchased 43 years later
2+2 gnatsuM 5691

+17 Tons of parts

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Re: Why don't our engines have cam bearings?
Posted by: joelsplace ()
Date: January 11, 2020 07:02PM

If you took much off it would be a problem but .010" shouldn't be an issue and it would straighten out the mains also.

Joel
Northlake, TX
5 Ultravans, 113 Corvairs and counting...

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Re: Why don't our engines have cam bearings?
Posted by: 63turbo ()
Date: January 11, 2020 08:02PM

joelsplace Wrote:
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> If you took much off it would be a problem but .010" shouldn't be an issue and it would straighten out the mains also.

I have no doubt that someone "could" completely re-machine a Corvair case like that, but I am a machinist and I sure as heck would NEVER do that even if cost, and time was not a issue, because I know that the centerline of the crank and cam would be off from were the factory had it, unless the customer wanted some crazy expensive tooling made. The issue is, you have to use the cylinder spigot sides of the block for your datum to cut the face of the case halves, and these are NOT good datums to use, and you have to take EXACTLY the same amount off each case half, and you've also ruined your original centerline so now you have to figure out that out before you force a new center through the case. I've heard of people "attempting" this on VW's before and although the engine ran it was way down on power from what it should have made because the centerline for the crank and cam was disturbed, leading to excessive friction. Blame the machinist all you want but it is way the heck harder than it seems. All to avoid buying a custom ground cam... which costs nearly the same as a stock new cam, or spray welding the cam and regrinding which is even cheaper or simply coating the original cam journals in the case with a anti friction coatings, or find another block... 150.00 or less for these other options.

I've only heard of one Corvair case line bored before, and although I cant remember if it was for the crank or the cam journals, they clamped a string straight bar on the existing bearings by re-bolting the case halves onto the bar (made to fit the existing surfaces) and then slid a cutter onto the bar and cut each individual bore, then moved to the next hole and fitted a sleeve to the hole that had been just cut (to provide extra support to the bar) then the next, add another sleeve and so on. Then made custom bearings for it... My understanding was they did it that way just to prove that it could be done.

------------------------------------

Kevin Nash
Friday Harbor Washington
63 Spyder, Daily driver, EFI read about my project here: [corvaircenter.com]
first test start on EFI here:[www.youtube.com]
first official EFI boost test here:[www.youtube.com]
My new fan! [corvaircenter.com]
engine less 62 Spyder
Canadian 64 Monza Parts car



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Re: Why don't our engines have cam bearings?
Posted by: joelsplace ()
Date: January 11, 2020 08:37PM

I can imagine that it is very difficult but regular V8 and V6 people do it all the time on main journals as part of "blueprinting". I realize it is a lot easier on those engines but a lot of your objections apply to them also.
It may be that they are harming more than helping.
The only shop I've seen do it on iron blocks ground some off each main cap and then used a long hone to cut them all at the same time.

Joel
Northlake, TX
5 Ultravans, 113 Corvairs and counting...

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Re: Why don't our engines have cam bearings?
Posted by: 63turbo ()
Date: January 12, 2020 08:50AM

joelsplace Wrote:
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> I can imagine that it is very difficult but regular V8 and V6 people do it all the time on main journals as part of "blueprinting". I realize it is a lot easier on those engines but a lot of your objections apply to them also.

I agree, in principle it should be the same, and if the Corvair case halves were as stiff as a typical water pumper block, then it wouldn't be much different. The fact that the Corvair case halves are basically jello compared to any water pumper block is what causes the problem. The block halves basically cant be trusted to be approximately straight unless it is bolted together and up to final torque with a crank in it, or a straight bar to "act"
like it. All of the other surfaces, are the same. On top of that, theres 2 locating dowel pin holes on each end of the Corvair case halves that are on position when the case mating surfaces are at their stock size... when you cut those, the dowel pin positions get moved closer together, causing the bell housing to not fit properly and will likely need to have those holes re-positioned "somehow" and then re-machine the bell housing surfaces with the whole assembly bolted up. These kind of things make commonly accepted practice for a water pumper block totally wrong for a Corvair block, especially when there's so many easier and cheaper options.

------------------------------------

Kevin Nash
Friday Harbor Washington
63 Spyder, Daily driver, EFI read about my project here: [corvaircenter.com]
first test start on EFI here:[www.youtube.com]
first official EFI boost test here:[www.youtube.com]
My new fan! [corvaircenter.com]
engine less 62 Spyder
Canadian 64 Monza Parts car



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Re: Why don't our engines have cam bearings?
Date: January 12, 2020 08:38PM

I’ll shed a little light on the align boring questions

On a water pumper block, a good practice is to cut 0.003”-0.004” off the caps, then align the shaft that runs the cutters so it is centered left to right, but is biased to the bottom of the bearing bores, as long as straight edge and feeler gauges didn’t show more than 0.002” “dip” in the block. Once you cut about 0.005” into the block, a tighter timing chain is required. (It’s been awhile, but if I recall they make -0.005” and -0.010” chains, but don’t quote me.

That’s all well and good for chains, but we have gears that intermesh in our Corvairs. This requires fixturing and a small enough bar to cut the cam bores, and you’d have to dial the cam centerline to be within factory spec for things to work, but we all know there had to be a reasonable tolerance on those dimensions to be able to be produced in the 60’s. If anyone has the drawings or knows the measurements between cam and crank centerlines, and what those respective bore sizes/tolerances should be, that would be appreciated, as I’ll looking into this for Project Pressurized Pancake. Getting everything on proper centerline and bore sizes reduces friction (cranks turn amazingly smooth in freshly align bored cases!) and gives you precise oil control by controlling these sizes.

Either fixturing or precise measuring is required for this for proper outcome, but in most situations it’s worth it. Something for thought is if you install the oversized ARP main bolt kit, most likely the extra clamp load will distort the bearing bores, requiring correction. Installing main studs vs bolts in BBC engines usually require align boring to correct the bearing bore distortion, but in the end, you have a tighter clamp load and a round bore, so the results are worth the extra work.

As far as the dowel locations, they’re probably a bit off even from the factory, and this is another dimension that would be good to know so it could be corrected. On SBC’s we had a fixture that put the dowels EXACTLY where they were supposed to be, but had special dowels that were oversized on one end and factory on the other. This took care of trans input shaft/bearing failures on high RPM stock car engines, and you’d be surprised how far blocks and bellhousings can be off from the factory. If you want to check yours, install the flywheel without the clutch, then the bellhousing. Set up a magnetic base dial indicator on the flywheel and indicate the transmission pilot hole, you may be disappointed...

I’ll see in the future if I can run mine through our engineering inspection lab to get a report on where they currently are. I’ll also do some digging in the manual for the other specs, it’s been a while since I’ve read it. My plan is to install the ARP fasteners to add clamp load, and anticipate the bores distorting.

Hope this clears some stuff up.

---------------------------------------------------------------------------------------------
You're unique, just like everyone else...

Johnny B
Central WI

Wife's '68, 3.0L, twin-screw compressor and fuel injected in the works...

Project Pressurized Pancake


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Re: Why don't our engines have cam bearings?
Posted by: dolomitefan ()
Date: January 13, 2020 04:25AM

My Triumph which is of OHC design doesn't have bearings either. They don't wear really bad but you can phosphor bronze them and then line bore them, or just find another head.

---------------------------------------------------------------
Mark Gibson, Staffordshire, England

1961 Corvair Greenbrier
1980 Triumph Dolomite Sprint
2009 Mazda MX5
2018 Infiniti Q30

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