Observations on a GT4 engine pull.

Rob, the custom exhaust valves came from an outfit called Manley Performance Products, Inc. They are actually a special stainless steel alloy they call Gen II 2600. They cost $80 each, about twice what plain stainless ones cost from Superperformance UK. Mike uses these valves exclusively in the blown Nitro and Alcohol engines he builds, and swears by them. I could have insisted we use the Superperformance ones, but at this point arguing over $150 and pissing off the machinist, whom I trust, doesn't make much sense.

The original intakes, after removing the carbon and polishing the shafts look perfect. We touched up the seat surface and they look like new.

Talking about money, for reference here's a pic of a brand new CNC billet head for a 426 Hemi waiting to go into a Top Fuel Nitro motor. At $3000 each we have competition for an expensive hobby. Valves, springs and rockers plus machining - $10,000. Just for a set of heads! I'm getting off cheap. Plus you have to buy two sparkplugs for each hole:
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I spent all afternoon yesterday in the machine shop with my spreadsheets of calculations. Mike had come to the same conclusion I had about setting the valve stem heights. We assembled the first valve in the head, then measured it with my tool. The reading was completely off my calculation. We measured again. Still twice what my calculations said it should be. Here's the spec from the Workshop Manual:

You can see that the distance from the top of the valve stem to the center of the camshaft is supposed to be 19.450 mm to 19.950 mm. We were reading 32.500 mm! But I recognized that 19.whatever number was on my spreadsheet - it was the number from the bottom of the camshaft journal to the top of the valve stem, not from the middle of the camshaft journal to the top of the valve stem. The Workshop Manual is wrong! Enzo, wassamatter you?

So then we assembled the valve, bucket and shim and put the camshaft on, and measured the clearance. It's supposed to be 0.20 mm - 0.25 mm for the intakes, 0.30 mm - 0.35 mm for the exhausts. It was zero because of the material we removed from the valve seats and the valve seating surfaces. OK, I could have corrected that by replacing the 4.00 mm shim we used for the measurement with a 3.80 mm, but I only have the 16 shims (of various sizes) I have from the engine, and if the rest of the valves might be tighter and require a shim below the minimum size shims available.

Mike says "Wait a minute," and goes to a shelf in the dark back corner of the shop and returns with two dust-covered boxes. "I thought I threw these away years ago. They're yours, a gift from me."

OMG! The Ark of the Covenent for 308 owners: A Box O' Shims! Pristine, with even the size stamps visible on the undersides. Wow!

What we decided to do is to pick a shim size in the middle of the range and grind the valve stems to accommodate that shim size at the top of the clearance (lash) range. The lash will tighten after a few hours of run time, and I plan on going back in and resetting them after a few hours of run time. I've got a good selection of shims now, thanks to providence and Mike's generosity.

The bottom pic is the stem grinder in action - you can take as little as 0.0254 mm off at a time using a vernier, so next week we'll go through the valves one by one and get them all set. Then we'll be able to get the heads together and put that baby back together. I'm figuring on some time in the Spring.
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Thanks for your offer, John. After the intake valves were cleaned up they looked pristine, and only took a very light touch to clean up the seating surface, so we decided to retain them.

Because of other priorities work had not progressed on the heads until yesterday. We had a productive day in Mike's shop, getting all the valves sized and the clearances set. The process we used is to insert the valve, then measure the stem top to camshaft centerline with the tool I made. We worked out a general range we want for this measurement, and had to grind between .005 and .030 (inches - Mike refuses to work in Metric) off the valve stems. This involves grinding the end of the stem in the valve machine, then relieving and polishing the edge so it doesn't rip the stem seal in final assembly.

The reason why we had to do so much work on the valve stem heights is because we machined each of the seats until they were clean, with no pits or scars. Several took more machining than others, Same with the valves, even the brand new ones. That means each valve stem height varied widely. Plus, according to Mike, each cam lobe might have originally be ground or have worn slightly differently. So each had to be fitted and sized independently.

Then the valve is put back into the head, the bucket is installed with a reference shim (3.80.mm for the intakes, 4.00 for the exhausts), and the camshaft is installed. We measure the clearance between the camshaft with feeler gauges, shooting for a 0.011" clearance for the intakes and a 0.014 clearance for the exhausts. The final adjustment is made by changing the shims. The actual clearance spec is 0.008 - 0.010 for the intakes, but I wanted to set it a little high because we think it will tighten up during break-in because of the geometry of the setup. The exhausts spec is 0.012 -0.014, so we set them to 0.014. After a couple of hundred miles I'll go back in to check and adjust them..

To do all 16 valves took us 8 hours, not counting the 2 hour lunch at the local burger bistro. Towards the end it became a game between me and Mike. He'd tell me the initial clearance and I'd tell him how much to grind off. "Are you sure?" "They're my damn valves, just grind it." Then I'd hand him the bucket and shim, the cam would go on and he would fan out the feeler gauges so I couldn't tell which one he was inserting.

"Ha!, twenty thousandths." So I'd hand him a shim six thousandths thicker (after I miked it to confirm it's thickness) and he'd measure it again insert the feeler and slowly turn it over to reveal the size - fourteen thousandths. Out of the collection of about 100 shims we have most are in the upper (thicker) ranges so I was shooting to get the ones we used in the higher ranges where I had more selection to work with. Mike implored me to never tell any of our mutual drag racing friends about the experience of working on "this damn Italian singer sewing machine." Most of the shims we ended up using were 3.80 for the intakes and 4.00 for the exhausts, pretty close to what was originally installed in the engine.

We did run into one problem, actually two - when I was inspecting the buckets I found two of them had hairline cracks. Bad, very bad. Luckily they hadn't progressed to the point where they damaged the bores they run in, but the wear pattern indicated they had been that way for some time. When heated they might expand and seize, hanging the valve open. They must be replaced, so I'm putting together an order for Superperformance UK and should get them in a week to ten days, and then we can get to work assembling the heads.

I did a search for "cracked valve bucket" and found only one thread that mentions it (http://www.ferrarichat.com/forum/308-328/449992-bad-mystery-engine-noise.html). The language in the thread indicates this kind of failure may be caused by a blocked oil passage. I'll be checking oil passages in the valve/camshaft system. All the other buckets showed what I think would be normal wear patterns, the top and bottom surfaces showing about 10mm of burnishing but still within the diametric spec. The bores looked OK but I will be scrutinizing them more before we assemble the valves. The buckets are #1 and #8, both exhaust side. Has anyone else run into this problem??? Here's a pic, look for the hairline crack in the shiny part of the bucket:
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No Photoshop. I was just rotating the bucket in my hand and felt the crack with my fingernail. Then we put it under the magnifier and saw the burnished (lighter area) wear pattern around the crack, and the crack clearly. I went through all the rest of the buckets using my highly calibrated sophisticated fingernail methodology and found the second one.

I've already ordered two replacements from Superperformance. They cost about $25 each and I'm wondering if I should replace them all. The shop is locked up for the next week or so, but when I can get back in there I'm going to experiment with Magnifluxing them to see if the cracked ones show up, and then check all the other ones.

I'm also considering polishing the buckets. The clearance between the bucket and the hole is spec'ed at 0,020 and 0,070 mm with an assembly clearance of 0,100 (basically four thousandths of an inch). That's pretty tight. The spec for the outside diameter of the thimble is 36,975 - 36,995; a 0,020 variance (less than one thousandths of an inch variance) so it's clearly a high precision situation.

I think I'm talking myself into replacing them all. I'm going to start another thread specifically about cracked buckets and see if anyone else can provide some insight.

 

I sent an email to SuperPerformance last week to up my order from 2 to 16 buckets. Now I can sleep at night. Chloe confirmed the change this morning. Bless that Lady!

Tim posted a picture of broken exhaust valves on this thread: http://www.ferrarichat.com/forum/308-328/472740-308-valve-seal-replacement.html#post143633241 (scroll down). Made me very happy I decided to do this job.

I'm replacing all the fuel hoses and coolant hoses. Got the fuel tanks drained yesterday and cut off the hoses on the bottom crossover pipe. The were in pretty good shape - no cracks, but brittle as hell. I'm going to go at the fuel filler hose today and remove the LH fuel tank so I can finally get the fuel level gauge to work correctly. With the tank out I might as well replace the long heater hose that goes through the chassis. Mission creep...

I checked the price for Gates Green Stripe 28441 hose and 25 ft at OReilly costs the same as 50 ft from RockAuto. I'm going to so some measurements today and see exactly how much I need. Anybody out there want to split a 50 ft order from RockAuto?

 

Thanks for the "Heads Up," Rob.I searched all your posts, but the search feature only goes back about two years. If you could dig up that info on that hose and your post on the procedure I would appreciate it.

Thanks, Mike

 

Uhhhhh... where? (It didn't come through on your post)
On your engine pull - maybe we can work something out. If you wait until the summer I'll even lend you my fancy 4 x 4 engine stand.

 

Thanks, Rob. Good article - I think I'll follow your directions and pull it from the front. I did find the Shieldsflex II 250-050 hose from an online supplier (eBay) for half the price West Marine charges. (Shields 5 8 in Marine Hardwall Water Hose per Foot 16 250 0580 1 | eBay).

 

I'm thinking of using the same stuff (in the correct size) to replace the vacuum hose as well - its non-collapsible, and looks to be pretty robust. My objective is not to build a concurs car, but a functional and reliable steed I can use. What do you think?

Misty at the Post Office called this morning - package from Superperformance is in, I'll have to drive into town today and pick it up. Maybe we'll get the heads done next week.