type IV compression loss on 3 and 4

[gatorjos]

My wife and I were cruising up I-5 toward Redding last weekend when she noted that she couldn't get the bus over 50mph. Headwind! I said, and the landscape is sloping while appearing level (a false flat!). She insisted something was wrong, so we pulled and switched places. I noticed the throttle didn't have the right pedal feel, so pulled over, adjusted the throttle cable (red herring #1?) and checked timing which was slightly advanced (9.5 instead of 7.5)

Off we went and the bus did seem to make better power and the gas pedal feel was normal. Then, she slowed down to 50 again. False flats and headwinds were a bit of a stretch at this point, and I could hear a whistling indicative of a header or head leak. The engine was idling great, but when I blipped the throttle in the back, blue smoke would dump out from the head at 3/4. Oh-oh...

Luckily, we were close to a friend's house in Chico so we limped 30 miles to his shop. I checked compression, and sure enough -- 35/40 psi on 3 and 4 while 1 and 2 had 135psi.

I decided to drop the motor and have a look.

It appears the head came loose somehow. A local shop had done a valve and ring job about 6000 miles ago and about 3000 miles in I re-torqued the head on the right side (which clicked off on all nuts), and foolishly I passed on checking the other head. I'll never know if that would have saved it, but oh well, here we are.

A solvent leak test had minor leaking from all valves, but overall things looked quite good. I brought the head back to the guys who did the valve job, and they are step cutting the head, putting in new exhaust valves, and lapping the intakes. The plan is to put the head back on, do some painting on the engine bay, and hopefully have the bus back on the road by the end of this weekend.

No, I did not check the case for pulled studs, that will be this weekend in Chico. I hope this is not the case.

On removing the head, I noticed the arrows on the cylinders point to each other, so either the engine builder or the local shop did not assemble the engine correctly. Question, do I correct this now that it is open, or leave as is? The current rings/hone job has 6000 miles on it, so it seems I might just leave it at this point. I wasn't planning on doing a ring job as well.

Any thoughts from the peanut gallery? I don't do this every day, so much appreciate advice.

The engine has about 45k miles on it from a fresh build with AMC heads.

_________________
1977 Westfalia Weekender Berlin "The Kitebus" aka " Colonel Mustard"

Previous romances:
1972 Ghia cabriolet (full body-off restoration -- stolen after five years of ownership)
2004 Passat 1.8T (manual)

http://21stcenturyhobo.com

[SGKent]

Sorry about the bad news. The thrust angles, and thrust surfaces are usually different. One side of the piston is usually designed so it is heavier than the other, and offset. If that is reversed then skirt and ring wear can be accelerated. That might be the blue smoke. A loose head normally would not cause blue smoke but worn rings, or a guide would.

The factory manual also states

[gatorjos]

[SGKent]

re pushrod - hydraulic is steel.

re pistons - Usually the piston is matched to the cylinder for clearance reasons. With worn pistons that need is less. As pistons wear there are three areas that come of concern. They can crack with high use. Uncommon but happens. The skirts collapse with use. If the collapse is minor a good machinist can whack them with a rawhide mallet and kinda put them back in shape. If they collapse a lot then they are worn out. Collapse means that the skirts bend inwards. That causes excessive rocking and piston slap. The ring lands wear out. That is common as the pistons age. Once the ring lands wear too much the rings start moving too much within the land. Quite often bargain builders don't check these things. Their approach is more it is what it is. From a quality engine builder's view it is more like putting new tires on a rusty bent rim. It will get you there but there is a difference. Myself I like to just replace the cylinders and pistons. However as parts become more unavailable there will come a day when that is not possible. I think right now I would try to rotate the piston and live with it, or replace the cylinders and pistons rather than pull all four and try to service them again.
_________________
“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[raygreenwood]

Also...aside from the pistons being installed with the arrows/offset incorrectly....if those piston numbers are "scratched" or scribed into the pistons...find whoever did that and beat them with a large, rusty shovel.

Scratching anything into parts that have that much thermal stress is a great recipe for cracking and erosion at the scratch points. Ray

[timvw7476]

Yeah, I know this is an elaborate set of torquing instructions, but I have
had zero issues with type IV heads loosening using this paper.
(mid 90's instructions,SIR failed to pay CA. L&I taxes, business closed)

[gatorjos]

Thanks for the replies everyone.

I like those torquing instructions. It makes sense to"sneak" up on the final value and keep working your way around. I do think I will retorque them all sheet some miles just to make sure.

I've been told both by the builder and the rework shop to not install head seals as the AMC heads allegedly don't need them. Does that ring true?

Also, since the head is being step-cut I understand I will need to add a shim at the bottom of the cylinder to offset the cut. I'll get to inspect the rings at that time, I guess. Maybe those are upside down too
_________________
1977 Westfalia Weekender Berlin "The Kitebus" aka " Colonel Mustard"

Previous romances:
1972 Ghia cabriolet (full body-off restoration -- stolen after five years of ownership)
2004 Passat 1.8T (manual)

http://21stcenturyhobo.com

[raygreenwood]

[Tcash]

Sounds like they are going to fly cut the head and then add the AMC step back into the head.
So yes, you need them to tell you how many thousands they flycut the head and add that amount of cylinder shims to the bottom of the cylinders.
Hell they should provide the shims for you.

Thnx mayor ratwell
Go down to head gasket
http://www.ratwell.com/technical/Heads.html

Good luck
Tcash

[Volswagon]

A comment on the S.I.R. sheet. Section 4.E. states the 'cut-outs' should face up.
According to Bentley, that is true for Type 1 rocker arms, but the slots should face down on Type 4, with the bevels away from the head as stated.
I have to wonder if the case decks have been checked. I'm not a fan of the hardware on stock AMC heads, especially valve seats..
_________________
I know the pieces fit, cos I watched them fall away.
Wanna hear God laugh? Just talk about your plans.

'75 Bus https://www.thesamba.com/vw/forum/viewtopic.php?t=697183&highlight=

[gatorjos]

[gatorjos]

Got the head back from the shop-- they ended up replacing both exhaust valve guides and seats, and fly cut the step down a bit to make it flat.

However, when I got back to the engine, I found piston four (that's actually facing the right direction) had scored the cylinder wall. I removed the cylinder to see if I could hone it out, which I nearly successfully did...and then I dropped the cylinder and chipped two fins.

I think that was fate trying to tell me to just get a new set of jugs and pistons as SGKent suggested already, so that's what I will do. Then I get to check the other head as well, which hopefully doesn't need anything since compression check was fine on that side.

Anybody have a good suggestion where to get quickest/cheapest Mahle cylinder set to NorCal?

_________________
1977 Westfalia Weekender Berlin "The Kitebus" aka " Colonel Mustard"

Previous romances:
1972 Ghia cabriolet (full body-off restoration -- stolen after five years of ownership)
2004 Passat 1.8T (manual)

http://21stcenturyhobo.com

[gatorjos]

after honing for a while

_________________
1977 Westfalia Weekender Berlin "The Kitebus" aka " Colonel Mustard"

Previous romances:
1972 Ghia cabriolet (full body-off restoration -- stolen after five years of ownership)
2004 Passat 1.8T (manual)

http://21stcenturyhobo.com

[raygreenwood]

[SGKent]

[Tcash]

If it did not run hot. The builder may have not cleaned the cylinders before assembly. The honing stones leave dust in the grooves. If not cleaned out the dust will wipe out the PC's.
It's up to the builder to clean the parts before assembly.

Good luck
Tcash

[gatorjos]

Just a quick update:

I got the engine back together and it appears to be running well and making good power. Compression after assembly was : 160-160-135-150. Not sure why #3 was a little lower -- if deck height is off by .010 would that do it? The shop that did the overhaul originally rebuilt the head for free -- they fly cut the cylinder seat a smidge to make sure it was put in new seats and guides, and ground the valves. Did get a new Mahle kit for jugs and pistons.

While doing teardown on the other side I noticed they had done me the favor of dropping the 1/2 head and breaking off two of the fins and cracking a third when they overhauled the topend before. Bentley says that's a pass, so I put it back together like that, with kind of low expecattions for this motor.

Now however, the oil light has been coming on at times. It goes back off when I rev it so it may be real. I'm planning on installing a sender and gauge so I actually know what I'm looking at, but jeez... Fingers crossed it's some gasket maker flakes floating by the switch.
_________________
1977 Westfalia Weekender Berlin "The Kitebus" aka " Colonel Mustard"

Previous romances:
1972 Ghia cabriolet (full body-off restoration -- stolen after five years of ownership)
2004 Passat 1.8T (manual)

http://21stcenturyhobo.com

[gatorjos]

I did add this sweet CHT gauge as well:

_________________
1977 Westfalia Weekender Berlin "The Kitebus" aka " Colonel Mustard"

Previous romances:
1972 Ghia cabriolet (full body-off restoration -- stolen after five years of ownership)
2004 Passat 1.8T (manual)

http://21stcenturyhobo.com

[timvw7476]

as far as oil pressure, I'll blame SanFran hills & aggressive cornering.
I'd keep the crankcase full, (topped off, maybe a full four quarts) & monitor it.
(oil loss) Thanks for the wrap up.

[Wildthings]