Lotus Elan

cometic vs ajusa / compression, 10,8mm cams needed!

PostPost by: el-saturn » Sun Jun 16, 2019 10:02 am

mornin' fellas! so the cometic lasted for 1/2hr. the ajusa can blow I F you don't skim yr head and especially if you're running rel. high compression. my swiss pal "gives" both head and block 2 bores each (4) and adds four guide sleeves (they slip over the head bolts at the bottom) whitch match head and block within a few thou!!

BTW: anybody have a pair of cams: 10,8 - 10,9mm lift in vg condition - could trade for a beautiful pair of 11,3mm
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PostPost by: JonB » Sun Jun 16, 2019 10:30 am

Do you think you could keep this on a single thread rather than creating a new post every time you want to ask about your head gasket? Would make it easier to follow.

Also, suggest you post a wanted thread for the cam.

Cheers
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PostPost by: el-saturn » Sun Jun 16, 2019 11:09 am

at age certain folks forget the last 50 to 100 contributions, so YOU DON'T; congratulations jon! - yes i have the age sandy
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PostPost by: nigelrbfurness » Tue Jun 18, 2019 9:37 am

Sandy, to be quite frank I'm surprised you got even half an hour out of a used Cometic head gasket. Let this be a lesson to all new and millenial readers, NEVER reuse a head gasket even if the engine has never run. If you want my advice, it's this: get the block skimmed and deburr the head bolt holes. Then pay close attention to the water ways in the head. If its an old head they will be corroded at the edges and maybe the distance between the edge of the water way and the fire ring has narrowed or become porous there. Weld them up, skim the head, redrill the waterways then light skim again. If your block is on 85mm bores then use the Ajusa 87mm gasket rather than an undersize one. The extra surface you've added around the waterways will compensate adequately for this and you should not have problems with the fire ring distorting as shown in your pictures. We've all been through these problems, some of us 40 years or more ago. Hopefully that will solve your problems.
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PostPost by: el-saturn » Tue Jun 18, 2019 10:13 am

nigel (sorry, but i have to say: i loved mansel!!)
the head just got skimmed 0,08mm (was enough: thank g.) then i lapped or cleaned all the valves (got 600mbar? vacuum on all of them) - however struggling with proper shims (the 4mm range!) on the outlet side // the intake are up to 0.25!! but she'll run. waitung for the new ajusa - block is flat (you can see 0,01 or zero) have a nice day sandy
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PostPost by: rgh0 » Tue Jun 18, 2019 10:49 am

Hi Sandy
With your high lift cams trying for 4mm shims is not usual. I suspect something else in you're head build is not the normal way to build a reliable high lift engine if that is what you're aiming for.

cheers
Rohan
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PostPost by: 2cams70 » Tue Jun 18, 2019 11:04 am

We still haven't properly identified the cause of the original Adjusa failure. And the compression ratio is still high - even higher now with the head skim. Is there enough confidence it's going to last this time around?
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PostPost by: rgh0 » Tue Jun 18, 2019 11:11 am

There is no reason why an ajusa gasket would not hold the compression ratio he has apart from a non flat head or insufficient bolt tension. Without knowing more detail on the head and more detail on how the head was assembled and retorqued its hard to tell which or both were probably causes.

The gasket appeared to not be centred on the bores either which could have also contributed but the failure mechanism does not suggest that damage to the exposed fire ring was the cause.

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PostPost by: denicholls2 » Tue Jun 18, 2019 1:58 pm

Note that the new skimming, though tiny, makes bottoming of the bolts more possible by the skim amount. I'm hoping Sandy has confirmed that the bolts do not bottom out. The thick shim sizes suggest to me that there is a risk of this.
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