BroncoII4x4.com

Posted: **Fri Jun 22, 2007 10:11 am**

Yes, I'm redoing the little 1987 BII motor. Please don't tell me I should be going 4.0 or more instead. i know thats popular.

I'd like opinions on:

1. Chilton says, .001-.002" piston to cylinder clearance. I have .005-.006" with freshly honed cylinders to stock 140K miles pistons(they look good).
Is that totally beyond acceptable or just "a bit on the loose side" ... but acceptable? (I really don't want to go all new pistons... I'm cheap).

2. Heads passed magnaflux test ... no cracks ... had no symtoms anyway. Any reason to not use 'em?

3. They need guides re-sleeved and reseating the valves. Shop says it's a can-do job. Anyone feel not a good idea?

4. going new lifters but old cam. Lobes look perfect...NO pitting.... so why buy new cam?

5. The thrust plate riding in the groove in the front of the cam.... locates the cam ...mine has .0004" front/back play. Chilton says .004" too I think. Is this a MAXIMUM play spec . I read where this is a big potential spot for oil pressure leakage ... which leads to starving lifters and "tapping". Is this a place I should try to get right down to MIN. clearance spec?

6. This motor had about 20psi oil pressure ..hot at idle. Still, with going with all new bearings ... prolly wise to go with a new oil pump, right?

7. I'm told the paper gaskets under the air plenum are imherant leak spots. Whats better than just new ones again there? Anyone prefer some other type of gasket anywhere else and what kind of sealers do you all like. Permatex non-hardening? The black Locktite High temp silicone? A locktite anerobic sealer/

Any knowledgable guys PLEASE offer any suggestions or things to watch out for !

Thanks guys, dave.

Posted: **Fri Jun 22, 2007 11:53 am**

bower100 wrote:Yes, I'm redoing the little 1987 BII motor. Please don't tell me I should be going 4.0 or more instead. i know thats popular.

I'd like opinions on:

1. Chilton says, .001-.002" piston to cylinder clearance. I have .005-.006" with freshly honed cylinders to stock 140K miles pistons(they look good).
Is that totally beyond acceptable or just "a bit on the loose side" ... but acceptable? (I really don't want to go all new pistons... I'm cheap).

ANSWER:
When rebuilding engines You are the ultimate quality control and you alone control what kind of product you have when you finish. Now that said I always try for the tighter specs. If you go too wide in the specs say over .0025 you will be susceptible to Piston slap, cracked skirts, Lots of blow by and higher oil consumption. Bite the bullet and do it right the first time.

2. Heads passed magnaflux test ... no cracks ... had no symptoms anyway. Any reason to not use 'em?

ANSWER:
If they are functional and not cracked or warper no reason not to use them.

3. They need guides re-sleeved and reseating the valves. Shop says it's a can-do job. Anyone feel not a good idea?

ANSWER:
Here is where a dollar comparison comes in. What is it going to cost to do the necessary repairs to the existing heads verses buying a new set of World heads. economics there.

4. going new lifters but old cam. Lobes look perfect...NO pitting.... so
why buy new cam?

ANSWER:
NO NO NO NO NO Never ever mix cam parts new and used or used and used. Cams and lifters are broke in and wear together. and this action actually hardens the lifters and cam. Now if you put a new lifter in it will tear up the cam lobe. or vice versa. Like everything it can be done and if you don't care if the motor needs a new cam in 5 to 10 thousand or earlier go ahead and do that. A main cause of lower oil pressure in the top end is Loose clearances and worn cam bearings. Don't forget to replace those too.

5. The thrust plate riding in the groove in the front of the cam.... locates the cam ...mine has .0004" front/back play. Chilton says .004" too I think. Is this a MAXIMUM play spec . I read where this is a big potential spot for oil pressure leakage ... which leads to starving lifters and "tapping". Is this a place I should try to get right down to MIN. clearance spec?

ANSWER:
If the book says .004 then I would check to see that it did not exceed that and not worry there. Main sources for 2.9 valve noise is lifters,and rockers. If you do not have the rocker mod done that would be a requirement. The rocker mod I am referring to is spacers on the rocker shaft to reduce side play.

6. This motor had about 20psi oil pressure ..hot at idle. Still, with going with all new bearings ... probablly wise to go with a new oil pump, right?

ANSWER:
Actually 20 at a hot idle is pretty good However,
I would not even consider re using the same oil pump. Why would you want to use a dirty worn out pump to circulate your engines life blood (OIL)?

There IS NO over the counter high volume oil pump for the 2.9. Buy a NEW Melling pump.

7. I'm told the paper gaskets under the air plenum are inherent leak spots. Whats better than just new ones again there? Anyone prefer some other type of gasket anywhere else and what kind of sealers do you all like. Permatex non-hardening? The black Lock tite High temp silicone? A locktite anaerobic sealer/

ANSWER:
Everybody has their own pet sealers and such that they like better. My own personal preference is to use what is called out in the Chilton's or Factory manual. I DO NOT use any type of sealer on any gasket if it is not called out for it in the book! People use way too much silicone these days..

Any knowledgeable guys PLEASE offer any suggestions or things to watch out for !

Thanks guys, Dave.

Along with my answer to your questions above here are a couple of tips.

Here is a bit of a reminder to do not forget to REPLACE the head bolts. These bolts are "Torque to Yield" bolts which means one use and they are history.

As I said earlier a complete engine major kit can be had from Cam craft and it includes pistons, Rings,cam etc. All the parts needed to "Do IT Right the first time. It is really reasonable price wise. My motto, If you can't do the best job you can repairing or fixing something then don't start.

Good luck and let us know how it goes.
The opinions listed are soley the opinions of The Tek At Large and should not be considered as absolute. I reserve the right to change my mind as I see fit.

Posted: **Sat Jun 23, 2007 8:42 pm**

I'm certified in engine rebuilding and have built quite a few.

Replacing lifters and NOT the cam is asking for failure. These have set to the original lifters. Hopefully you removed them and indexed them to the lobes? If not, you should replace the cam and lifters as a set. The new lifters will set to the old cam and will probably chew the old cam up. I'd give it 500 miles. Go by the specs on everything else. Your piston clearance will be set by the piston manufacture. Like TRW, factory pistons will be differant and also differant piston compounds(forged,cast) will change the clearance requirements. Just go with specs, and PLEASE don't reuse old cam.
garagedude

Posted: **Sat Jun 23, 2007 8:49 pm**

If you were in the hospital and they noticed a possible heart problem would you want them to replace the valve or use liquid bandage on it??

Please replace the oil pump. Your engine will thank you later..

garagedude

Posted: **Mon Jun 25, 2007 10:12 am**

Thanks guys ... good info...,

1. The oilpump will be new ...( I was just "fishing" for the odd opinion of actually re-using the old one.)

2. The cam .... Ok... it'll be new. Definetly new lifters , ... (the 2.9 a habittual tapper ).

Important Question: The old cam journals and the bearings both look real nice. But Ford does calls for ONLY .001-.002" clearance there, ( snug compared to other moters...prolly because of the issues this motor has getting oil pressure to the lifters and above).

This said, .... because the two middle bearings are blind ... hard to get to. if the front old bearing ends up measuring within speck with the new cam, would I be nuts to not replace all 4 cam bearings?

3. Also, I had acess to sevice bulletins on this motor from a rebuild association. One recommended a "trick" to help up oil pressure by as much as 4 psi. The cam thrust plate has a narrow channel cut into the backside of it ,where it bolts to the face of the front of the engine block. It's intended to deliver oil to the groove in the camthat the plate rides in. Bulletin says to flip plate over 180* , so it faces out, to effectively do away with that oil passage. ( Apparently addequate oil bleeds from the front cam bearing to lube this plate. ) Sound like a good idea? This is a major motor rebuilding association

4. Pistons to cylinders clearance ... pistons look nice ...I still feel the factory radial grooves in the piston sidewalls ... even low on skirts. I did a fresh finish hone on cylinders ... all wear marks gone ... even right at top of bore. Now honed cylinder to old piston measure .005-.006" at wristpin height, 90* out from pin ...(Chilton new spec calls for .001-.002").

Go ahead and tell me .... am I totally nuts leaving those "somewhat loose pistons in there? Look now, this was going to be a budget rebuild. The new cam ... ok, .. >$100, .. but new pistons/ and rebore ,.... now were adding like $300. Please tell me the motors not a ticking bomb with a bit sloppy pistons. Of course I'd be doing new std. rings ... so clearance would end up decent ... only an extra 004" ... I can live wuith that.

Look at it this way, if you tore a moter apart and found .005-.006" clearance, would you be saying... WOW it was sbout ready to let go! Just trying to be relistic here. ... not building a Nascar motor.

But, if I'm nuts ... say so. Chilton gives no max tollerance.

Thanks Dave

Posted: **Mon Jun 25, 2007 7:28 pm**

You should replace all the cam bearings. A LITTLE piston slap will not hurt your "time frame" of life on your motor. However, not only the piston/wall clearance important but the PISTON WALL TAPER very important. As the piston travels up and down the cylinder the oil is scraped off by the rings. Also the compression rings are keeping the compressed air and fuel mixture in, they help pull fuel/air in for the compression stoke. Usually you have two compression rings and one oil ring. If the cylinder wall is tapered from wear then the rings must adjust if you will to the wall every time the piston travels up and down. These rings follow the taper of the wall every stroke. After a while (you guess how long) the rings get tired of adjusting to the wall taper and don't do it any more. Also at higher rpm's they may not seal as well because they are constantly changing diameter to stay against the wall. If you can obtain an inside micrometer and measure the cylinder wall at the top and at the bottom. This should be done about where the 2nd compression ring stops at the bottom and the top. You should ck with ford on cylinder wall taper allowances. You will use less oil and build better power with zero taper on your cylinders. I've seen motors with .006 piston clearance and .015 wall taper. They didn't make good power and used some oil after awhile. Garagedude

Posted: **Mon Jun 25, 2007 7:38 pm**

Also ck your ring land clearance. There's a clearance between your rings and the "lands" of your pistons. If this is worn your rings will "rock" in your pistons and while traveling in tapered walls they will wear the edges of your rings off, which will greatly reduce power and increase oil usage. I know this is not good news that you want to read, but I've been there, rebuild old motors and had to scrape to save money to rebuild it right. Garagedude

Posted: **Wed Jun 27, 2007 9:09 am**

006 piston clearance and .015 wall taper.

You meant .0015" right?

When I measured , I checked four places in the bore where the piston rings travel ... from TDC to BDC ... 0* and 90* out from pin.
Combining all the six cylinders ...each measured at the four spots, (24 total measurements,) tightest spot was a tight .005" and loosest was a loose .006" . (No one bore had more of a variance than .0001").

In plain words, no ring will work to seal more than .0001" bore variance.

No expert here, that sound pretty fair ?

Again, does anybody know where I can find a Ford ,( or reputable),recommended MAXIMUM piston-to-bore tollerance? (Just want to know where my .0005-.0006" lied in the acceptable range)

The piston ring groove to ring clearance. Yeah, I failed to check it yet... I remember seeing it in the Chilton book, too. I'll check with a feeler when I get the rings. ( I've already ordered new standard rings....hoping/planning to use 'em. ...hope they can be can be sent back if I must go 1st. with o/s pistons).

Anyone hear about the "inverted thrust plate" modification this motor rebuild association suggests?

Again , thanks to knwledgable guys offering up info.

Dave

Posted: **Wed Jun 27, 2007 1:36 pm**

I forgot the zero, sorry, anyway, I think you have an extra zero, but sounds like your piston walls are in good shape. Good luck on your rebuild

Posted: **Fri Jun 29, 2007 1:14 am**

here is a site that will help you know what clearances are allowed on the 2.9 liter if your interested ........ scroll toward the bottom and it has a lot of 2.9 engine specs on it .....

http://www.broncoii.org/techpages/2.9sp ... index.html

maybe there is some thing there that might help on clearances with the rebuild

Posted: **Fri Jun 29, 2007 11:44 am**

WOW,

I went to the link to just look over the stuff and I'll be danged, I wrote that page!!

I was once a Mod on that site and I put that info together for Brian several years ago.. Wow I am Global!! ha ha ha.

Posted: **Sat Jun 30, 2007 3:06 pm**

lol ...... thats kewl ...... but i thought it might be usefull to him

Posted: **Sun Jul 15, 2007 11:34 am**

Well I'm finding out what life's like when you choose to rebuild a motor. I started out planning to do it with ecomomics a strong consideration. (only replace whats really needed).

Well, the more time you invest in the job, the more inportant doing it totally right becomes Ya know,...time is money too.

Sooooo, I'm replacing pistons too. Borderline ring end gap and ringland slop bugged me. .5mm oversize will still give the mach. shop plenty of metal to remove. And, .... Mr. new lifters .... meet Mr. new cam .... everybody ... you all get new bearings to live with.
All the other new stuiff was in the plans all along.

Side note, I don't think this motors ever been apart, but the rod and main bearings that were in it were both at .010" under. (my crank journals are nice enough to not need work ...just go back with new .010" under bearings).
The oem Ford motor at .010" undersize doesn't surplise the shop manager. Not totally unheard of for manufacturers to take a bunch of crankshafts with journals that did not meet std journal dimentions when ground and do a run of new motor assemblies with ground down journals.
I haven't started reassembly, waiting for the heads and block but I'll repost as job progresses.

Last item: does anybody know if theres aftermarket exhaust manifolds out there ... flow better than stock ? Just a thought.

dave

Posted: **Sun Jul 15, 2007 12:53 pm**

Hey there Bower100,

I am glad you are going to "Do The Right Thing" and rebuild it right. One of the benefits of going that way is you will have a motor you can totally rely on for many many miles..

On that undersize crank that may be the result of a Field warranty replacement. I had a friend many years ago that was a manager for Ford. He told me that when they had to warranty a motor they would sometimes repair it in the shop. They also had available short blocks that had been put together using whatever they could find. these "Warranty engines and parts were used to reduce the dealers warranty costs. All of that equipment did not get the same warranty. Most of the time the parts were at most 6 months.

All of the off the line vehicles had engines that were all up to snuff spec wise. It was when the field shops did their magic would you see these engines.
As for the exhaust manifolds there is is no option except to go to headers. I bought a set of headers from summit that were coated and the cost was real reasonable.

Good Luck and be careful,

The Tek At Large

Posted: **Sun Jul 15, 2007 4:48 pm**

Good to hear from you.... and seriously, thanks... your one of the guys who kinda "pushing" me to not cut corners.

The Summit headers .... I just thought the stock cast "boat anchors" were crude looking ...horrible flow characteristics .... and headers would be an obvious power improvment.

Wonder if anyone on the forum site might have a set they had used on their 2.9 and then went to different motor?

I'D BUY 'EM.

Dave

BroncoII4x4.com

Rebuilding the 2.9 litre ... general and specific questions.

Rebuilding the 2.9 litre ... general and specific questions.

Re: Rebuilding the 2.9 litre