1973 Rebuild

[Takhli]

It’s been a while but we're back with more info on the engine buildup. And, since the lower end is pretty much done, we're starting to look at cylinder head reconditioning. Matt may have addressed some of this over time and I questioned the P90a to P90 conversion but bear with us...

Matt wants to use either the P90 or P90a Cylinder head because they are said to have better flow and combustion chamber characteristics. He and I looked all over for a head we could use, buying more than one, only to send at least two back to the sellers. I thought a warped head or one that had been surfaced too many times would be the big head ache but the biggest problem turned out to be corrosion.

Five heads and two engines later, when our buying frenzy was over, we ended up with one P90 and two P90a heads to choose from. None of the heads were warped but one P90a has been surfaced and needs 0.015 shims under the cam towers; the P90 has some minor issues with intake/exhaust manifold gasket surfaces (minor corrosion); and the second P90a has some pretty bad corrosion around a few coolant passages. All three heads need valve work, including new valve guides but all can be reconditoned. Otherwise, teardown showed that every rocker arm was shot and the hydraulic cams were badly pitted.

Matt bought new OEM rocker arms and I sent all three cams to Iskendarian for evaluation. Isky had the cams for about four months and I had to call on their status at least five times. When I finally got hold of Ron Iskendarian he appologized, had the P90 cam polished, and then shipped all three back without charging us a dime. I'd say he did us right.

Because the head gasket surface on our second P90a is the truest, and because our machinist tells us he can clean the surface with a 0.003-inch cut after welding up the corrosion, we decided to repair that P90a. But, like almost everyone else rebuilding an engine, we're limited to mechanical cams and need to make the modification that fits the smaller diameter mechanical pivot posts.

The mod is well known (except to me, before I started this project), and it's documented on the internet in more than just a few places. But while researching I came up with a few questions, such as: How to control pressurized oil seepage from under the pivot post; supporting the upper part of the Time-serts; and the mileage-life expectancy related to both those questions.

The question of oil seepage is easy to fix with short pieces of aluminum dowel in each oil gallery, inside the pivot post bores. The plan is to turn the dowel material to the same outside diameter as the inside diameter of the oil gallery bores; freeze the dowels for an hour or so; warm up the cylinder head to about 120 degrees in momma's oven (I didn't say that) and then tap the cold dowels into each gallery of the warm cylinder head. When temperatures equalize the interference fit should keep everything in place. (When I get to that point, I'll post the photos and narative.)

For the same reason that the pivot posts need oil pressure, about ½-inch of depth within the pivot post bore is larger in diameter than the threaded area below. That makes installing threaded inserts easier but leaves most of the insert without mechanical support.

 

Comparing a P90 head with a P90a (below left and right, respectively) there is about 50% less surface area to support a mechanical pivot post if installed in the P90a.

Also, using the threaded insert in the P90a only provides about three threads – just 2.25mm or so – where the head material supports both the Time-sert and the mechanical pivot post. 

Time-serts used to modify the head are about 1/10-inch smaller in outside diameter than the pivot post bore and their installed height must be below the face of the boss. With a higher lift cam, the sweeping action of the cam lobe against the rocker arm is bound to increase lateral forces against the Time-sert. To eliminate the void we need either a machined sleeve around the threaded insert, or something lke an epoxy to fill the gap. Matthew and I decided to use machined aluminum sleeves but the cost would be enormous...

...So,I made about sixteen sleeves in my garage, using not much more than my drill press, my calipers, some files, and sand paper.

Here's an installed sleeve in a P90a pivot post bore.

Twelve sleeves cost me about $35 in materials and about 18-hours of time (because I didn't have a lathe). Not bad, I think.

Method to follow, later.

Cheers.

 

Edited April 13, 2017 by Takhli
duplicate photos and narrative

[Matthew Abate]

Made some progress toward flipping this thing upside down: back hatch and windshield are out.

[Takhli]

Very cool. Glad you didn't find any hidden rust.

Good work!

[Matthew Abate]

Doors off. Ready for the rotisserie after some minor garage reorganizing.

[Takhli]

Making Time-sert Sleeves for a P90a - to P90  Rocker Arm Pivot Post Conversion: 

First, I bought an M22x1.5 tap and a length of 7/8” aluminum tube from the hardware store. An 8-foot length of tubing cost us $32 and the tap cost $28 - much less than labor and materials to have a machine shop make the sleeves. The tap matches the external threads on the Time-sert and the inside diameter of the tube is large enough to accept the tap without drilling it out.

 

The tap won’t cut  the full thread depth because the tube’s wall thickness is just slightly too thin; however, that is okay because it makes tapping the tube easier. The reason we need the sleeve is to fill the void between the time-sert and the pivot post well. Sealant and epoxy will make the installation firm so we only need the finished sleeve to thread easily onto the time-sert and fit closely against the pivot post well.

“Soft-jaws,’’ used to hold hydraulic fittings, held the aluminum tube in the vise but the tube still slipped when we ran the tap in.

 

Wrapping the tube in 80-grit abrasive cloth provided a better grip but we still had to take small bites with the tap – maybe two or three turns – before backing the tap out to clean things.

Cutting oil is an absolute must. Eventually, the tap cuts enough treads to make four or five threaded sleeves, then we cut 6” off the threaded end of the tube and started over.

   

At least three 6"-lengths of tubing are needed for twelve sleeves, and each must be turned to an outside diameter of at least 0.550-inch. Below you can see the diference in diameters, between a partially finished sleeve and the original diameter of the tubing. Its not much.

Without a lathe, we used a drill press and homemade spindle setup to do this. I cut the hexagonal head off of an M10x1.75 bolt I found at Ace hardware, cleaned up a damaged lower part of an adjustable pivot, and sacrificed a Time-sert to install over the pivot threads.

This made up the drive spindle that fit into my drill press, but we still needed a way to hold and center the opposite end of the tube. I used hard maple to make a tight-fitting plug, fit into the opposite end of the tube. This gave me something relatively soft to bear against a live center (You can find  a live center at a wood worker’s supply store; they are used in wood lathes to turn dowels and spindles.)

 

Then, I chucked the live-center vertically into my drill vice and bolted the vice to the drill press to keep the whole setup in line and rigid.

With the live-center mounted, and the vice bolted to the frame of the drill press, I could turn down the spinning tube with a coarse file and various grits of sand paper. I took measurments often and when the diameter was right, I cut the tube in pieces approximating the sleeve length. 

There is a bevel in the P90a pivot post well, near the top of the threads; to match this, each sleeve is given a bevel on its lower outside diameter so it dropps into the pivot post well as far as possible. Also, the inside diameter of the top end was chamfered to let the time-sert thread as far into the sleeve as it could.

   

Total time to make 12 sleeves was 16-hours. Not bad.

We will make the installation tool from an M22x1.5 bolt. I'll show that later, when I post the sleeve installation.

Hope this helps. Cheers.

 

 

 

Edited May 11, 2017 by Takhli

[grannyknot]

@Takhli that's pretty clever, hope Matt's paying you well for your work

[Matthew Abate]

[mention=31325]Takhli[/mention] that's pretty clever, hope Matt's paying you well for your workLOL

I'm going to make sure the home I put him in when the time comes has a female staff. Should cover it. Hopefully he won't notice when I steel all his tools.

[siteunseen]

4 hours ago, Matthew Abate said:

I'm going to make sure the home I put him in when the time comes has a female staff. 

A cat house with a Viagra gumball machine would put a nice shine on my golden years. 8^)

[Captain Obvious]

Nice work on the inserts. What are you planning to use to lock the inserts in place? I'm no expert in the field, but I've had (mostly) good luck with the Loctite Bearing and Sleeve (which is green). You mentioned Loctite green earlier. Is that the stuff you were referring to?

I also don't know how large of a gap it will deal with, but I have had situations where it cured on me with a half installed bearing race. I was using it as belt and suspenders on a reasonably well fitting bearing and I got it half pressed on and it flash cured and wouldn't go no more. Happened to me twice with the same pair of parts. I found the solution was to make the fit sloppier. I bet if I would RTFM, I would figure out what I was doing was a problem.

Point is... It would really suck for that to happen to you with a half-inserted spacer. Took me heat to get things apart again. Look into it maybe before you go for it? I don't think the bearing and sleeve retainer is intended to be wicking after assy. The green thread lock is, though.

Also... WD-40 - Worlds best cutting fluid for aluminum!    Sorry, I'm rambling.

[Matthew Abate]

11 hours ago, Captain Obvious said:

Point is... It would really suck for that to happen to you with a half-inserted spacer. Took me heat to get things apart again. Look into it maybe before you go for it? I don't think the bearing and sleeve retainer is intended to be wicking after assy. The green thread lock is, though.

GREAT CATCH! We will do our best to not fall into this trap now.

[Takhli]

18 hours ago, Captain Obvious said:

Nice work on the inserts. What are you planning to use to lock the inserts in place? I'm no expert in the field, but I've had (mostly) good luck with the Loctite Bearing and Sleeve (which is green). You mentioned Loctite green earlier. Is that the stuff you were referring to?

I also don't know how large of a gap it will deal with, but I have had situations where it cured on me with a half installed bearing race. I was using it as belt and suspenders on a reasonably well fitting bearing and I got it half pressed on and it flash cured and wouldn't go no more. Happened to me twice with the same pair of parts. I found the solution was to make the fit sloppier. I bet if I would RTFM, I would figure out what I was doing was a problem.

Point is... It would really suck for that to happen to you with a half-inserted spacer. Took me heat to get things apart again. Look into it maybe before you go for it? I don't think the bearing and sleeve retainer is intended to be wicking after assy. The green thread lock is, though.

Also... WD-40 - Worlds best cutting fluid for aluminum!    Sorry, I'm rambling.

Hi, Cap...

Initially, I tried to get the inserts as tight as possible but found that with my "lathe" I couldn't be as accurate as I wanted. That said, the sleeves really have a drop-fit into the pivot post well. I'm thinking the clearance varies from 0.002 or so, upto maybe 0.005. Not more. 

Green Loctite would be what I would use if I had access to a lathe or had the sleeves manufactured by a machine shop. Then, we could have kept the tolerance really tight. Now, though, we are going to use the best epoxy (heat and expansion stable) that we can afford. Maybe that will be good old JB Weld, but I don't think so.

I did find some high-quality epoxy by 3M that is very expensive for the amount we will use - I may have mentioned it earlier but can't remember the part number or name. However, I need a really good epoxy to install a few chassis stiffening compontents on my Mustang, so I think I'm going to re-research the stuff and if I find it will hold up to the engine heat, use it for Matt's cylinder head, too.

I do know that we want the sleave to fit so that the Time-sert will run freely into the pivot well, matching the threads in the head. The insert can't be run all the way up to the top of the Time-sert because it (the Time-sert) will control that match-up. We can't have a situation where the Time-sert tightens up above the machined face of  cylinder head. That in mind, I need to go very easy with whatever epoxy we choose.

 I know exactly what you mean about the green stuff flashing halfway through an assembly process. I used green locktite to assemble various components during my work on drone engines (really small stuff we manufactured on site).  I'm in Tucson and found the stuff is really heat/humidity sensitive, as far a cure is concerned. Work in the coolest dryest environment you can find if you have need of the green stuff again.

If you have trouble with it flashing too fast, try the locktite de-bonder; its thinner than the locktite and as long as you catch it fairly quickly, it wicks into the smallest gaps. In the worst cases, we would need to let our parts sit in a bath of de-bonder over night, but we always got them apart.

I think I may have used 99.9% pure Iso-propol Alchohol for this purpose as well, but can't recall.

 

Edited May 12, 2017 by Takhli

[Captain Obvious]

Thanks for the tips on the Loctite. I'll keep that stuff in mind next time this job comes up. I was installing bearing races onto antique motorcycle magnetos and that sort of work doesn't come along every day!

Keep up the good work!