Twink Head Forensics

[edgefinder]

I've been taking apart cleaning up putting away sub assemblies. Last weekend the head came off. 28,000ish miles hasn't run in 30 years. It's been off before and I bet the PO is still cussing Lotus and the mechanic. Me I love the thing. I can imagine the guys 50 years ago in a small shop and I wonder who said lets do it, we can make a head and it will work.
I was hoping all parts would be useable and most are. It looks like someone didn't have a clue about valve shims. 3 or 4 spring caps show hammer marks from shims floating around. A couple valve ends are beat up and a couple smeared from no clearance. Valve guides were knurled in a spiral pattern, all worn out, one is way big.  Valve stems some are ok but a couple worn bad. Debris dents in 1 and 3 combustion chamber edges. 1 has matching marks in piston. They will clean up easy. One bucket looks bad but I can grind it back, cams are good. A 2 groove .360 intake, 1 groove .350 exhaust. Head is fine no corrosion, gasket was sealing good. Gouges from flipping head around on chain tenshioner. 4 head bolt holes were tapped maybe to hold for guide knurling? I'll clean up the rest of the motor and reassemble with light valve springs to measure and see where it was before I freshen it up

[Roger]

Sounds like you have a Sprint D-type inlet camshaft. Good modification.

[buzzer]

A few things to ponder.  Can you regrind the face on the buckets. Are they not case hardened? Also effect the shim size. With a bucket like that I’m surprised the cam is ok.
The knurled guides. The only reason I would think for that is that the guide holes are oversize.
On the pic of the valve seats. It’s difficult to see but the inserts seem to be inserted too deep in the head. Not sure what the solution is for that. New oversize inserts?
To me I would suggest you get this looked at by an expert.

[jbcollier]

That's a seriously worn head.  Looks like the tappets are "rocking" in their bores.  You should fit all new guides, valves, retainers and any damaged tappets.  However, first have the head thickness, head true, springs, valve seats, tappets and tappet bores tested and/or checked.  No use buying parts for a scrap head.

[dakazman]

  I did see a twin cam head for sale . It says local pickup only.😕

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F133204227198

Dakazman

[EuropaTC]

That's a bit of an anomaly, from what I can see the waterways are excellent with no visible corrosion, but everything else looks like the head has been to the moon and back. I've never seen a cam follower so badly scuffed and, as John  said, it's surprising the cam is still usable after that.

The valve seats look from the photo to be too far down in the head, all mine and photos I've seen in books show them roughly level with the combustion chamber.  Together with the damage to the valves it makes me wonder if it's been assembled without shims, or perhaps someone "turned up" a shim on a lathe out of mild steel because they didn't have a hardened shim of the correct size ?

The cast iron valve guides used to be reamed after fitting, so maybe that accounts for the marks you can see. I don't know if that's still the practice and some of the bronze (?) guides you can get don't require that stage.

It sounds like you have 2 different cam profiles (2 groove was the "sprint" cam, 1 groove was the "special equipment" cam). I've not checked so this is a guess, but I thought the valve lift and overall timing was the same on both, it was the open/close ramp which made the difference.  Having had both cams, the sprint (2 groove) is the one to have, so I'd budget for a matched set.

The more I think about if, the more I come round to the idea that someone has decided to "tune" this head. I can't imagine why it would need to come off at 28k for any other reason, so that makes checking the head depth (as John posted) something that must be done.  The manual shows standard depths and how far you can go, so it's worth checking someone hasn't decided they know better.  It will be a real shame if it needs welding to restore a usable compression ratio.

But as for re-using valves/followers, I'd give up on that idea. All parts are available so I'd fit new guides, seats, valves and cam followers.  I suspect you'll need new cams as well looking at that follower.  Probably not what you want to hear, but it's a lot of work if one of those reclaimed parts gives up 1,000 miles down the road.

Brian

[jbcollier]

Forgot about the photo with the valve seats.  Ouch, they are toast and will need replacing as well.  Sorry for all the bad news.

[edgefinder]

Sounds like you have a Sprint D-type inlet camshaft. Good modification.

Yes that's the best part of all this

A few things to ponder.  Can you regrind the face on the buckets. Are they not case hardened? Also effect the shim size. With a bucket like that I’m surprised the cam is ok.
The knurled guides. The only reason I would think for that is that the guide holes are oversize.

The buckets are thin so I think hardened through. I had to lean it in the light to show the damage and it kind of magnified it. They all have .003"-.004" dish from wear and the damaged one measures hardly .001" more. I'm a fix what's broke and run it guy so will grind bucket, put valve in with light spring, put dye one and check for full contact. I'll get at it with the right lapping paste if I have to. The guides are tight but look knurled inside. I've heard of it but never seen. I'll get a pic of it

That's a seriously worn head.  Looks like the tappets are "rocking" in their bores.  You should fit all new guides, valves, retainers and any damaged tappets.  However, first have the head thickness, head true, springs, valve seats, tappets and tappet bores tested and/or checked.  No use buying parts for a scrap head.

This ranks number 2 or 3 for most heavily abused doing maintenance motor i've taken apart. Buckets all measure 1.3745" middle 1.374 ends. Six bores are 1.3755" two are 1.3765" or .0005" out of tolerance, I bet it was like that new so I'll run them for now. Heads flat and full thickness but valves guides seats all need replaced. I'm calling Dave Bean's later for a catalog.

  I did see a twin cam head for sale . It says local pickup only.😕
Dakazman

I got this covered. My favorite hobby is bringing vintage race bikes back to life at the track.

everything else looks like the head has been to the moon and back.

The valve seats look from the photo to be too far down in the head, all mine and photos I've seen in books show them roughly level with the combustion chamber. 

It sounds like you have 2 different cam profiles (2 groove was the "sprint" cam, 1 groove was the "special equipment" cam). I've not checked so this is a guess, but I thought the valve lift and overall timing was the same on both, it was the open/close ramp which made the difference.  Having had both cams, the sprint (2 groove) is the one to have, so I'd budget for a matched set.

Brian

There a mindset in this part of the world that pushrod V8's are it. When I was hauling it off the crowd was saying it needed a small block in it. The same kind of guys must have worked on it.

In Wilkins book page 136 and 140 it looks like mine. I think in some pictures they've been ground blended in, too much in some.

A little more intake cam than exhaust should be good. I'm curious how different the timing is between the completely worn out chain and a new one. If you track the car how long does a chain last? Or is mine dead from over tightening. 

[jbcollier]

Please have someone experienced with twin cam heads replace the worn seats.  If the shrink fit is not right, the heads will crack.

[edgefinder]

Please have someone experienced with twin cam heads replace the worn seats.  If the shrink fit is not right, the heads will crack.

JB, I understand your concern. It's a garage so I'll show how I gauge things and put stuff together. I think my name throws people off. I pretty much live in a machine shop and an edgefinder is used to find parts on a mill. The only valve seats I've replaced were on a worn out ex Ferrachi Ducati F1 750. It had a bad history but I raced it reliably for several years and won a championship. Around the same time Gurneys indy car team were having head crack problems. I was asked behind the scenes to bid on making 100 from bare castings with extra material. I work with one of those guys now who maintains 2 of and supplies parts for the fastest corvettes in svra. When I ask who built something he always says Some Guy so maybe I should use that. My friend Some Other Guy just built iron heads for the black car in the video. Hand hammered the seats .006" interference no preheat, I couldn't believe it
https://www.youtube.com/watch?v=1LZlwFUwcTM

[edgefinder]

Sorry for the rant but I honestly know what i'm doing. These are simple motors but leave a lot of room for error. I'm used to race maintenance where you do whatever needed to avoid problems later. I took a bmw m10 head to experienced experts for a 3 angle valve job when I was young. I told them the seats were hard and don't flycut the mating surface. They chuckled. When I picked it up the seats looked worse and they had cut the surface. The old guy at work watching me running an indicator across it had warned me of this. They were mad I ruined their seat cutters and when I said hows the cam going to fit if the bores aren't parallel to the new surface they got madder. Then I gave them a bunch of money so I could leave. I worked at the new high tech cnc shop and I had the new machining center. We had a lot of visiting engineers come through and they liked to look at my bike behind the machine and whatever home project taking up half the machine table. Somebody liked the head clamped to an angle plate top and bottom cam bores lined up and I was boring the middle one back to center for a press in bearing. We made a bunch of fixtures for Mercury Marine for the 1984 corvette motor because of that. The deal with the indy car heads was them asking me the kid in the shop about machining them before they asked the bosses. I told them we didn't have a machine for cam bores and they said what if we get you one.

[BDA]

It's ok, edgefinder. I think JB was just trying to warn you of a potential problem because he didn't know what you know. As you found out, not all machine shops will even do what you tell them much less know how to deal with a fairly rare foreign motor.

I'd say your experience speaks for itself and when you mentioned Gurney, I knew you weren't going to hurt yourself

Please keep us informed about how it's going!

[edgefinder]

Yeah, I should have said Geez guys it's not dead it's just moving really slow

[BDA]

 

[Chuck Nukem]

Please have someone experienced with twin cam heads replace the worn seats.  If the shrink fit is not right, the heads will crack.

JB, I understand your concern. It's a garage so I'll show how I gauge things and put stuff together. I think my name throws people off. I pretty much live in a machine shop and an edgefinder is used to find parts on a mill. The only valve seats I've replaced were on a worn out ex Ferrachi Ducati F1 750. It had a bad history but I raced it reliably for several years and won a championship. Around the same time Gurneys indy car team were having head crack problems. I was asked behind the scenes to bid on making 100 from bare castings with extra material. I work with one of those guys now who maintains 2 of and supplies parts for the fastest corvettes in svra. When I ask who built something he always says Some Guy so maybe I should use that. My friend Some Other Guy just built iron heads for the black car in the video. Hand hammered the seats .006" interference no preheat, I couldn't believe it
https://www.youtube.com/watch?v=1LZlwFUwcTM

That is way too cool. Did you get the job to make those heads?