T4 engine - all of a sudden, 1/4" play between rocker and valve?

[raygreenwood]

[raygreenwood]

And actually...no...really....the seats are not prone to falling out when the engine i cold. It would be more correct to say the seats falling out when HOT ...not cold is "common"....not "normal".

Aluminum contracts a greater amount than steel. When the head is cold....is when the dimension of the valve seat pocket is at its smallest and compressing on the less contracted steel seat the most.

Likewise when the aluminum is hot...its expansion rate is greater than the steel seat. You are most prone to losing a seat when the head is hot.

And....this all forgets the fact that the seats have been installed with an interference fit.
The problem is that with age....and that does not mean the aluminum gets old...it means with years....and millions of strikes of the valve pounding on the seat.....along with tens of thousands of heat cycles (mostly the heat cycles)....and since most metals but especially aluminum and magnesium...are "work hardening" materials.....the aluminum which is already under tension from the interference fit....will eventually expand and contract enough to lose its thermal "elasticity".

So its not "normal"....for seats to fall out. It is COMMON...after many years of heat cycling.

And...if the interference fit were somehow too small...say like under .005"....this can happen even quicker.

Also....a while back in another thread...a few of the type 1 "guru's" in the performance forum...flat out stated they use .008" to .010" interference fit on many type 1's they build.

That...is too much for a type 4...and a portion of what SHOULD be used for interference fit...directly depends on what the alloy of the head is....and what the alloy of the seats are.....bluntly...the expansion rates of both need to be taken into consideration.

The reason I mention this....is because....structurally type 4 heads cannot HANDLE that much interference fit. Because interference fit does not JUST transfer stress in a radial fashion around the circumference of the seat....it is VERY hard on that thin ledge underneath teh valve seats that type 4's have.

Add that stress...to the stress of installing the seat on that ledge...because at .010" interference fit...even heat expanding the heads and chilling the seats with dry ice...will not be a "drop in" install...you will have to press them in. That along with interference fit can crack that ledge.

So....along with a lot of heads with a zillion miles and heat cycles.....we have heads floating around out there that have been built by type 1 mechanics with ball peen hammers. More land mines.

The seat i recently bought for the 1.8L build I am using...bronze alloy seats....the manufacturer of those seats has good experience in the 914 world.....and has explicit numbers for interference fit for THEIR seats...in our heads. They are between .0055" minimum and .0075" maximum.
Ray

[Wildthings]

Once the seat begins to move it no longer dumps heat to the head as readily and thus gets very hot compared to the aluminium of the head, this tends to keep it somewhat in place when the engine is running, but once the engine cools off the seat cools and ends up loose.

A seat moving in the head makes an audible noise, which a practiced ear can pick up on. With the seat moving there is also a loss of performance as the subject cylinder will not breath as well.

[raygreenwood]

[MikeyM73]

Ok, so I knew this engine was in fair to poor shape but this probably didn't help . This thing was thrashed. This is what you DON'T want the inside of your tin to look like. So if your Vdub has been sitting for a while, check the tins!! Mouse turds, bedding, a spark plug, a few screws, nuts, washers, 2 oil covered wasps and all. This being my first time dropping a bus engine went pretty easy. My buddy has a jack pad with extendable arms with square rubber pads that I slid outward, centered under the heater boxes, removed the tranny nuts/bolts and it slid straight back. I tell you what - you need every mm to get the engine to slide back enough to clear the trans input shaft.. I had to remove the top timing scale bolt and then it slid back enough to lower down. Oh, and the gouged aluminum to the lower rt of cyl. 3 (plug removed) = compliments of the PO dropping a plug down there.

The 2L will be coming out of the parts bus this Saturday and my dizzy, intake, and exhaust will go on to get it fired and tested. Anyway, just wanted ya'll to have a good laugh with all the CV19 badness going on.

Stay safe, be well.

Mikey
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'73 Pop-top Westy, found sitting in a field for 10+ years, cleaned up, rebuilt furniture, reloved. Original 1.7 block/fully polished crank, 93mm 1.8L balanced AA pistons & cylinders, new 1.8L balanced rods, HAM 42/36 heads, Scat C25 cam & lubalobe lifters, Dual HPMX40s, R2C filters w/ Outerwears pre-filters, functioning thermostat & flaps, Pertronix Flamethrower III, 4-1 exhaust w/ Cherry Bomb 2" turbo muffler & OEM heater boxes, averages about 19-22ish on the highway.

[busdaddy]

That's rather tame compared to some of the examples I've encountered, but still not what a happy aircooled engine should look like. At least they didn't leave a spark plug on top of the oil cooler to eat it's way through into the juicy part.
_________________
Rust NEVER sleeps and stock never goes out of style.

Please don't PM technical questions, ask your problem in public so everyone can play along. If you think it's too stupid post it here
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[Mispeld]

Since I'm getting older, I've pulled and installed the engine and trans twice now as one unit by myself. Sure, it may take an extra hour but I reduce the amount of four letter words I use. It's much easier to mate the trans to the engine out of the bus rather than the motor to the transmission inside the bus... for me anyway. It's great to see you making progress.
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Tom
1977 Westy. 2.0 Fuel Injected.

[Wildthings]

I agree that isn't that bad. Sometimes there isn't enough room for another acorn cap up under the tin.

[ivwshane]

I’ve never seen intake manifolds wrapped like that before, what would be the reasoning behind it?
_________________
77 westy 2.0 FI
69 ghia coup 1600dp
70 single cab

[crownline]

Looks like some sort of Macgyver pre heat system
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1972 Bus 1700 cc Single Carb. But not a progressive.
Barelymuvin
Wish I still had the ones I got rid of.

"It"s got some dings and dents and neither of us is going to SEMA."(Update, I went to SEMA in 2019 but the Bus stayed home)
[url=http://www.vw-mplate.com/mplate-8446.png]Click to view image[/URL]

[MikeyM73]

Hey, I'll take that as a conmpliment Yes! Yes it is! That my custom, hi-performance, ghetto warm-air box / header wrap setup. Works pretty well. The Weber Proggy came with the bus but was WAAY out of tune. So knowing it needed heat, I just came off the hot air riser for the OEM air cleaner with a 2" flexible tube into a corrugated aluminum box that I installed under the carb base, fashioned something up to trap the heat, jetted and tuned more, and it works pretty well ..no stumbling and it's not super rich. It doesn't get the base of the carb scorching hot but it gets luke warm at worse and extremely warm at best. I seem to be right about in the range of jetting compared with the folks who run the Weber Progressives with some type of pre-heat set up and it runs well and transitions from the idle to main circuit smoothly and doesn't bog or stall on acceleration so I'm happy until I can go to dual 40s.
_________________
'73 Pop-top Westy, found sitting in a field for 10+ years, cleaned up, rebuilt furniture, reloved. Original 1.7 block/fully polished crank, 93mm 1.8L balanced AA pistons & cylinders, new 1.8L balanced rods, HAM 42/36 heads, Scat C25 cam & lubalobe lifters, Dual HPMX40s, R2C filters w/ Outerwears pre-filters, functioning thermostat & flaps, Pertronix Flamethrower III, 4-1 exhaust w/ Cherry Bomb 2" turbo muffler & OEM heater boxes, averages about 19-22ish on the highway.

[MikeyM73]

So as I'm stripping down the '78 FI 2L, I ran into my first surprise - I'm sure you guys are already aware of this - on the 2L the mechanical fuel pump boss is there but its not drilled for the pushrod nor is it tapped for the bolts. So I guess this means I'll need to run an electric pump... which is kind of what I was playing with anyway... take some drag of the cam, like back in my old Chevy days.
_________________
'73 Pop-top Westy, found sitting in a field for 10+ years, cleaned up, rebuilt furniture, reloved. Original 1.7 block/fully polished crank, 93mm 1.8L balanced AA pistons & cylinders, new 1.8L balanced rods, HAM 42/36 heads, Scat C25 cam & lubalobe lifters, Dual HPMX40s, R2C filters w/ Outerwears pre-filters, functioning thermostat & flaps, Pertronix Flamethrower III, 4-1 exhaust w/ Cherry Bomb 2" turbo muffler & OEM heater boxes, averages about 19-22ish on the highway.