Align Bore?

[Fishcop]

Along the vein of a similar thread....

I did a trial build of my bottom end last night using my straight/magnafluxed and polished crank and old bearings in my freshly machined case. When I pulled the engine down several months ago I did the test of putting the crank back in and torquing everything back up to see if there was any distortion... it seemed fine, so I didn't have it align bored.

My crank seems to bind when I torque up the nut inside the chain section of the case. Every other nut and through bolt torques up fine and allows me to turn the crank by hand except when the number 7 journals are tightened. I can turn it with reasonably light pressure on a socket at the front pulley.

Is this normal or should I have the case align bored? Is it possible that a light hone will still allow me to use standard bearings I've already bought?

Cheers

[garibaldi]

If you are using your old bearings to do this check, you may have swapped bearing shells this time when you put your old bearings back in. The old bearings wore in in their original position, and if you swap them in the case now, they could pinch the crank if you tighten it up.

You really should use the new bearings from this point on. The old bearings are just that- old. The best way to check the line bore is with a accurate bore gauge. As far as straighness, dont bother, its not, none of them are, especially the older cases with some mileage on them. The line bore housing gets bananna shaped and bows in the middle. Any of the quicky line hones that guys are paying for out there show this, the hone will not touch all the way around and it will leave shadows, and on top of that make the housing oversize. The only proper way to line hone a 911 case is to clip the case halves flat, and then hone the main housing back to standard size, then resize the intermediate shaft housing and the seal bores. One other option that would require less work would be to go to first over main bearings in the case, which would allow the hone to true the housing back to proper dimensions. The issue here is that the last set of oversize bearing I was able to source was about $800. At that point, I would rather do the case halves and just run a standard size bearing, it would cost more this way, but not that much more, and then you know that the case halves are fresh and straight as well.

I think if you measure you housing sizes now, that you will find that the dimension is at or near the edge of the recommended wear limit, so if you leave all else alone and have the case line honed, the housing will be oversize and beyond the wear limit, and will still be crooked at that point, so in actuality all that you would be getting are some scrathes in the case, making the housings oversize, and you lose a percentage of the crush on the bearing shells.

And, clipping the case halves requires sophisticated setup and equipment, The case half must be set up level with the spigots and the mains to insure that the block will still be parallel from side to side and front to back. Not done on a giant belt sander as I have seen people do.

Garibaldi Imagineering
10 Central Ave
Madison NJ 07940
973-377-4210

[Fishcop]

Thanks for the response Christian. I did indeed mix up the bearing halves... I just pulled them out one at a time from a bag of old parts So hopefully this is the problem. I will use the new bearings tonight and try it out again. Will it ruin the bearings?

As you suggsted, the cases are never straight, but I guess I'm wondering just how much "bind" on the crank is acceptable. I was turning the crank over by hand (without the fly wheel for leverage) right up to when that one journal was torqued. Having said that, I don't think I followed the correct pattern on the bolts either, so maybe this is an issue also?

Thanks again

[911pcars]

You can also try modifying the tightening pattern so the crank doesn't bind. See if that helps (with the correct bearings in place).

Sherwood

[garibaldi]

You can use the new bearings, lubricate them with some oil or STP so you dont spin a dry crank on them. Measure the main housing sizes without the bearing, and then measure the main bearing clearance with the bearing s installed so you know excactly where your at. If you dont feel comfortable doing this or dont have the proper equipment, then have someone who knows what they are doing measure, and show you so you can see for yourself. As far as how much force should be required to turn the crank if its binding- well there should be no binding, it all depends on how much hp you want to waste trying to overcome the added fricition in the case from the crooked housing. I have done line hones on engines where after the shear of the oil on the bearing is broken and the crank is spun, it will coast down gradually to a stop for a few seconds. And these engines will speak well of the effort put into them.

[Fishcop]

I don't have the gear or knowledge to measure

I'll give it a go tonight with the new bearings and Sherwood's suggestion, but if it is still binding I'll head to the machine shop... no point starting this rebuild half-assed.

Thanks Christian and Sherwood.

[911pcars]

As Christian suggested, maybe you can check yourself. Get some Plastigage and check each main bearing for clearance. Cost is about a buck for the item and your time with a torque wrench. You can see for yourself whether the case isn't straight, although you should probably "mike" the main journals too.

Sherwood

[Fishcop]

Well I put the new bearings in and lubricated them and then mated the case halves.... same There is strong stiction when I try to turn the crank, but once that is broken it seems to turn relatively easily, but certainly does not spin down over a second or two, but rather immediately. I tried changing the tightening pattern as well but it didn't really help.

Bearing in mind I live in a location that does not have any Porsche knowledge among the machinists here, what is my next step? Should I still try having it align bored just enough to stop the binding or will this just complicate my problem with a lack of crush on the bearings? There are aircraft machining shops at the airport... could these guys help given that the Porsche engine is quite similar to what they'd be working on?

C'mon guys give me some "happy" stories of how you had a similar problem, but it didn't effect your rebuild!

[PJMARKOW]

Hi John. I had my case line bored by Porsche Centre Melbourne, and they supplied the oversize mains and No. 8 bearing. Maybe you should try Porsche Centre Brisbane, they might do the same or be able to recommend someone. My case was an aluminium 3 litre turbo case, so even these can go out of spec after many miles of use. If you've gone to the trouble of stripping it down etc, may as well do the job properly and have it measured and line bored if required.

[Fishcop]

Hi Paul

I've already purchased the main and #8 bearings for standard as the crank came up fine, I didn't realise the case would be an issue. But as you say, if it needs it, that's what I'll have to do.

May I ask a ball park figure on the boring and OS bearings?

[garibaldi]

Take the case back apart and look at the new bearings, you will find some shine on the areas that the journals touched, most likeley if you plot out the wear, you will see the alignment is off at either end, and even see that the main saddles are cocked. Why dont you start there and take some pics and put them up or send them so we can see what you have. Oversize bearing are pretty expensive. My recommendation would be that the case be clipped and resize the main housing back to standard. If you are going to spend the money for oversize bearings, you may as well spend a bit more and get the whole case mating surface renewed, that way you kill two birds with one rock. You still have to have the case measured both for the housing dimensions as well as your bearing clearances, otherwise you are just shooting in the dark.

[Wayne 962]

FYI - you should get a copy of the Engine Rebuild Book, which details all the steps that you need to take to make sure your case is correct and true.

First off, assembling the case and spinning the crank is *not* a good method for determining whether you're good to go or not. The engine will expand and contract heavily when hot, so a go / no go test on a cold engine is of limited use. Garibaldi is right - the case needs to be either overbored (expensive bearings) or trued using the method pioneered by Walt at Competition Engineeing (www.competitioneng.com).

If you ignore this problem, it will not go away...

-Wayne

[garibaldi]

Wayne, I must go back to a previous post on this topic where I had already stated that the proper way to correct main housing alignment is to flatten the case halves. This requires a very sophisticated approach to insure that the case remains square. Now you are pressing me into a corner here to tell you what I see wrong with your recommendation. I am not here to criticize other peoples methods of doing things but if you are going to make recomendations to people in here to read your book, or go to a specific site and follow what you say, well I would make sure I recommended the best approach for the best results. The process you are recommending leaves a lot to be desired. Maybe its best that we stop right here.

[J P Stein]

At risk of offending the experts, I'll give you a happy story.

To shorten this, my rebuilt 10 years ago and sat on a shelf 2.7L long block had evidence of binding.

Upon Mr. Weiners recommendation, a trip to Dan Hall's in Portland for a drag hone eliminated that problem. These cases tend to collapse the main bores perpendicuar to tha case split...in line with the thru bolts. The drag hone does not oversize the main bores, just returns them to roundness/straightness....cylindricity, if you wanna get technical. Bout 100 bucks.

A good P-car machinist can tell you if it will work on your case.....many are too far gone (twitsed) for a hone....in which case, get another one.

I've been thrashing the motor for 2 years without any problems.

[garibaldi]

Without any offense taken, nor am I considering myself an expert by any stretch of the imagination, I just want to express my frustration with the fact that you had a shop sell you on that service, or "Drag Hone"

To quote a statement from my previous post up a few levels-

The line bore housing gets bananna shaped and bows in the middle. Any of the quicky line hones that guys are paying for out there show this, the hone will not touch all the way around and it will leave shadows, and on top of that make the main housing oversize.

I hate to be the bearer of bad new, but what you essentially paid $100 for was to have a shop run through your main housings with some type of hone that did little more than put some scratches in it. I would bet with the utmost certainty that the housing size was not at proper size afterwards, nor was it any starighter. Unfortunately the motor is together, so there is no way to tell, and its running and you are happy with it. Just know that next time you go to have the mains corrected- a shop that knows how to do that properly would advise you that they couldnt even set up for $100, let alone perform a proper line hone.

[Fishcop]

I am now very sad

Wayne, I do have your book and have read it cover to cover, however I am one of those "weird" people that live outside a big city and choose to drive a car that a part from being 35 years old, has no one other than me to keep it on the road. I don't have access to Walt or any other Porsche gurus, so everything I do I have to plan well ahead

Christian, your advice has been excellent and I am not ignoring it, merely "edumacating" myself!

JP, I have heard similar stories of engines going back together with "slight binding" and no problems for 1000's of miles. I'm pretty sure this won't be the route I take at least until I speak to a machinist. At least I know there is at least one machine shop in Oz according to PaulM.

Thanks guys, I'll let you know how I go.

[J P Stein]

Yes,Mr Garibaldi, I read and understood your opinion.

I spend 8 hours a day in a machine shop running a CMM and have for 16 years. I have acess to every machine measuring tool imaginable and know how to use them.....and did....but thanks for your opinion.

[garibaldi]

Then your ears should have pricked up when you were sent to a shop to have a line hone, or drag hone what ever that is done for $100. If you are familair with machining, you know how involved setup can be and for a shop to set up, hone, verify the measurements- all for $100, that would make me wonder. But I could be wrong. I am sure that you measured the case before and after and made sure that evertyhing was OK.

Every 911 case I have ever worked on, especially the magnesium ones are not only crooked, but oversize or right at the limit. SO most of the guys that talk to me and tell me that they are doing a rebuild on their 2.7 911 and just paid a couple hundred bucks for a line hone, make me shake my head. SO having a line hone done, one where the case just gets bolted together and rubbed through with a honing bar or sort will not only make the housing even furhter oversize since it will remove material, but will do absolutley nothing to aid in straighteneing the holes, but now you have oversize maybe slightly straighter holes. To remove enough material in one of these instances to get the housings straight would make them so far over spec it is not possible. The only way to do this is to clip the halves and bring the housings back up to standard size with the proper equipmement- which is definetely not for $100.

[garibaldi]

Here is a picture so you can see what I am talking about, you can see how the hone didnt even hit all the way around in this housing, so there is no way it is round. This is a $300 line hone a guy paid to have done at a "machine shop", so imagine what $100 gets you. I am not trying to be disrespectful, but this is what we see out there. You be the judge. I am just trying to make you aware.

[Wayne 962]

Originally posted by garibaldi
Wayne, I must go back to a previous post on this topic where I had already stated that the proper way to correct main housing alignment is to flatten the case halves. This requires a very sophisticated approach to insure that the case remains square. Now you are pressing me into a corner here to tell you what I see wrong with your recommendation. I am not here to criticize other peoples methods of doing things but if you are going to make recomendations to people in here to read your book, or go to a specific site and follow what you say, well I would make sure I recommended the best approach for the best results. The process you are recommending leaves a lot to be desired. Maybe its best that we stop right here.

You obviously didn't read my post at all - I agreed with you. Please read the posts carefully before you post a reply.

-Wayne