Cylinder head gasket
Discussion
The general rule of thumb with head gaskets, not Esprit specific, mind you, but just head gaskets, is that you should check the head for being flat and then skim it if it is not. Doesn't hurt to check the block deck as well. I would never skim a head just because it was off, especially on a motor like the 9XX's where you can't just run down to the breakers and pick up a spare head or three. HG's can blow for a number of reasons, one of which is a warped head.
Dr.Hess
Dr.Hess
All of the 907 heads I do work on seem to need flattening, the alloy is fairly soft and tends to warp easily if the head gasket isn't torqued down exactly right. The problem tends to be worse when the old (steel/asbestos) head-gasket is used. Sometimes the head will only need .002", sometimes .010".
Good 9xx specific mechanics are hard to find. I do engine work on Jensen-Healeys and actually have a 910(converted to n/a) in my car. However, I'm in Atlanta...that would be a long drive from the NE.
Judson Manning
DLC Motorsports Div
Atlanta, GA
Good 9xx specific mechanics are hard to find. I do engine work on Jensen-Healeys and actually have a 910(converted to n/a) in my car. However, I'm in Atlanta...that would be a long drive from the NE.
Judson Manning
DLC Motorsports Div
Atlanta, GA
Lucas,
Lady Jane is quite a looker!
I became a 907 mechanic out of necessity. I used to race Jensen-Healeys and needed a way to pay for my habit. Eventually, I began working on other people's cars and don't have the time to race any more.
There aren't enough JHs around to make it a full-time thing for me, and all I do is full rebuilds, so I still have my day-job. Most of the work I do is out of my house, so don't expect a lavish shop with flowers in the men's room. Care to grab a drink and talk shop?
Judson
Lady Jane is quite a looker!
I became a 907 mechanic out of necessity. I used to race Jensen-Healeys and needed a way to pay for my habit. Eventually, I began working on other people's cars and don't have the time to race any more.
There aren't enough JHs around to make it a full-time thing for me, and all I do is full rebuilds, so I still have my day-job. Most of the work I do is out of my house, so don't expect a lavish shop with flowers in the men's room. Care to grab a drink and talk shop?
Judson
Hi,
The maximum a 907 head should be skimmed is 0.002", beyond this, the head isn't serviceable. If you don't know if the head was previously skimmed, assume it was and go no more than 0.001".
Aside from a strength issue, skimming the head will bring the cam pulleys and crank pulley closer together and upset the timing spec. A heavily machined head or block will often require a switch to adjustable pulleys to get the timing right again.
Happy Motoring! ...Jim'85TE
The maximum a 907 head should be skimmed is 0.002", beyond this, the head isn't serviceable. If you don't know if the head was previously skimmed, assume it was and go no more than 0.001".
Aside from a strength issue, skimming the head will bring the cam pulleys and crank pulley closer together and upset the timing spec. A heavily machined head or block will often require a switch to adjustable pulleys to get the timing right again.
Happy Motoring! ...Jim'85TE
lotusguy said:
The maximum a 907 head should be skimmed is 0.002", beyond this, the head isn't serviceable. If you don't know if the head was previously skimmed, assume it was and go no more than 0.001".
The 910 head can be milled 0.015" per the manual. I don't have the 907 data handy to corroborate this, but 907 heads are generally cut to a max limit of 0.020"
The maximum warp limits before milling is required are:
0.25mm (0.010") = longitudinal full length.
0.12mm (0.005") = longitudinal between 1&2 or 3&4
0.06mm (0.0025) = transverse
Less than that is acceptable.
More than that requires milling the head.
If the head deck face is warped, then the entire head is warped. If the deck is milled, then the cam carrier faces should also be checked for flatness and milled the minimum amount required to achieve flatness.
Lotus lists optional cylinder head gaskets B911E0291 & B911E1292 that have one and two additional laminations respectively. Each lamination adds about 0.009" to the gasket's thickness. B911E1292 is 0.018" thicker and should be used with heads that have been milled to the max. However, that's the old steel/asbestos laminated sandwich style gasket. The current spec gasket for turbos is the Goetze composite unit and it's not available in a thick version.
Head Depth = 82.04 +/- .254mm from block joint to cast pads.
__________ = 3.23" +/- 0.01"
910 max cut = 0.015", per the manual.
907 max cut = 0.020", unofficial/ typical max
Cut no more than necessary to achieve flatness !
A907E0026Z = standard steel/asbestos head gasket
B911E1291 = one extra steel lamination.
B911E1292 = two extra steel laminations.
B912E7029Z) = composit made by Goetze in Germany and was developed specifically for the Lotus 910 Turbo 4-cylinder. It does not have a metal face at all. Only available in one thickness.
lotusguy said:
...skimming the head will bring the cam pulleys and crank pulley closer together and upset the timing spec. A heavily machined head or block will often require a switch to adjustable pulleys to get the timing right again.
Milling the head deck will retard the MOP on both cams. A 0.015" cut will retard it about 3 1/2°. A 0.020" cut will retard it about 4 2/3° (crankshaft degrees... cam specs are always in crankshaft degrees).
For cams that are supposed to be timed to a 104° MOP like the 107 cams in the Turbo 910 noted in Ian's original post, an option to aftermarket adjustable pulleys is to install different Lotus pulleys.
Installing the 100° MOP (blue dot) pulley on the intake cam will advance it 4°. Similarly, installing the 110° MOP (red dot) pulley on the exhaust will advance it 6°.
Since later Turbo 910's came with various combinations of red/blue pulleys (varied with the years), you may already have the pulleys required. If you were thinking about swapping your emissions pulleys to 104 MOP (green dot) pulleys to improve performance but now find you have to skim the head, keep the original pulleys. You may be closer to your 104 target with them on a milled head than with the green-dot pulleys.
Regards,
Tim Engel
Lotus Owners Oftha North
Esprit2 said:
If the head deck face is warped, then the entire head is warped. If the deck is milled, then the cam carrier faces should also be checked for flatness and milled the minimum amount required to achieve flatness.
I didn't word that well.
The surfaces on top of the head where the cam carriers sit should be checked and/or milled. Not the cam carriers themselves.
Regards,
Tim Engel
Lotus Owners Oftha North
rlearp said:
Tim that matches what I have in the manuals on the 907. Just looking into that now in fact.
Ron,
The Technical Data section of the Esprit S1/S2 manual leaves out a lot of info. The TDA Section of the 1983-87 Turbo Esprit and S3 Service Notes (Workshop Manual) has a lot more detail. Find a G-Turbo owner in your area and make a copy of the TDA pages. Or send me your mailing address offline.
Then other fragments of info show up in different manuals. For instance, the allowable warp specs I quoted show up in the 1988-92 Esprit Turbo Service Notes, but not in newer or older manuals.
Regards,
Tim Engel
Lotus Owners Oftha North
Minnesota, USA
Judson or anyone else with good 907 experience - how much milling leads to what compression hike?
I have a number of heads around here but I'm port matching one of them and plan to have it decked. If you know of a safe rule of thumb, such as 0.045" off leads to a hike of 0.4 points, that would be helpful.
Otherwise I can get a buret from the lab and cc everything to figure it out.
Also, at what point in milling do you run into piston/valve interference problems? Again, I can check this with clay but I'm just looking for some guidelines here.
Thanks much,
Ron
I have a number of heads around here but I'm port matching one of them and plan to have it decked. If you know of a safe rule of thumb, such as 0.045" off leads to a hike of 0.4 points, that would be helpful.
Otherwise I can get a buret from the lab and cc everything to figure it out.
Also, at what point in milling do you run into piston/valve interference problems? Again, I can check this with clay but I'm just looking for some guidelines here.
Thanks much,
Ron
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