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Author Topic: CAA Gipsy's warning CAP1700  (Read 293 times)

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Offline john henderson

  • Posts: 273
  • Country: gb
CAA Gipsy's warning CAP1700
« on: Sunday September 09, 2018, 20:59:07 UTC »
I take it you have all seen the latest CAA pronouncement about 100ll v UL91 fuel, bronze heads and reduced longevity (the engine-not you!), Carol de Solla Atkins has started a survey on her Chipmunk website as to who uses which fuel and what have been the experiences and it has produced some interesting comments.

Personally, we use 100LL as that is what is available at base airfield; we did try UL91 some years ago, but experienced continued plug fouling. We went back to 100LL and have had no trouble since.  our engine is now up to 1100+ hours and seems fine -touch wood.

Does anybody know what the CAA based their analysis on?
john h

Offline Nigel Stevens

  • Moderator
  • Posts: 245
  • Country: fr
Re: CAA Gipsy's warning CAP1700
« Reply #1 on: Sunday September 09, 2018, 22:16:56 UTC »
I'm outside the UK and this document was pointed out to me on Friday. I use 100LL in my Chipmunk. As background, I started my career as a research and development engineer on piston engine fuels and lubricants in the oil industry. I have a few comments on the document, which is actually  very poor  IMHO.  *** RANT BEGINS****I am personally suprised it was let out the door. It looks like a draft writtened by a Summer student trainee.  Rough running is used as a term and technically that is a very vague description of a problem, which can have many different causes. Low compression, felt  in turning the engine by hand, should have been picked up, before it gets that bad, by a leak down test during regular maintenance.  The advice against using MOGAS is valid however, both for the reason stated, since alcohols and esters put into mogas, attack some of the elastomers (synthetic rubbers) used in seals and pipework.  What is not mentioned is that the storage life of mogas is measured in weeks . Left in tanks over  a winter for example deposits will form and potentionally block pipework and passages. This was brought to my attention by the company that repairs all my motorised garden equipment here in France, where it is recommended, in the garden equipment field, to drain the tanks for winter storage of mowers and other gasoline powered tools. The storage stability requirements for AVGAS are much more stringent so it can be left in tanks for longer periods. Leaded gasolines, like 100LL, contain scavengers, chemicals of the halide family, which are designed to removed lead and other deposits and prevent plug fouling. UL91 does not contain scavengers, since it does not contain lead, so I'm not surprised that plug fouling may be more prevelant with UL91 than with 100LL. The final icing on the cake is the recomendation to have the engine maintained by someone who has the skill and knows the engine, seems like a statement of the obvious.  As to bronze cylinder heads, without valve seat inserts, being particularly sensitive, it would be nice to know if the wiriter is refering to seat burning and guttering or valve recession or some other vague illness. In passing we are refered to the engine technical manual, which says nothing about any of this!  If the person in the CAA, who wrote this document, wants to send me a PM, I'll be happy to give him some free education over the telephone.***RANT ENDS***
A good evening to everyone

Offline speedbird1

  • Posts: 545
  • Country: us
Re: CAA Gipsy's warning CAP1700
« Reply #2 on: Monday September 10, 2018, 02:18:58 UTC »
Well said Nigel, Go get "em!!

Some tin pot expert given free reign by a boss who doesn't have a clue.

I thought bronze heads had long gone although the seat inserts kept some of them around for a while.  That memory was from about 30yrs ago when I come to the states???

We can get Mogas without Ethanol etc. so are a bit better off although mine always ran on 100LL.

The requirement for knowledge and skill???  That is becoming harder to find.
Speedbird 1.

Offline buchan

  • Posts: 39
  • Country: ca
Re: CAA Gipsy's warning CAP1700
« Reply #3 on: Monday September 10, 2018, 03:00:24 UTC »
That is one of the least informative technical documents from an aviation authority I have ever read.  The confusing reference to bronze heads, without acknowledging that most are aluminum, and not subject to this most of this advisory is really misleading and alarmist.  The lead issue with bronze heads has been known for more than half a century.

Nigel's "Rant" is spot on.


Offline john henderson

  • Posts: 273
  • Country: gb
Re: CAA Gipsy's warning CAP1700
« Reply #4 on: Monday September 10, 2018, 15:15:46 UTC »
Spoke with Deltair, (the Gipsy licence holders), who tell me there are still a number of bronze headed Gipsies (conjures up a lovely bucolic picture), and they are still doing rebuilds of same.  They all get steel insert valve seats.
john h

Offline Dick Gower

  • Posts: 301
  • Country: au
Re: CAA Gipsy's warning CAP1700
« Reply #5 on: Tuesday September 25, 2018, 07:11:46 UTC »
I'm still laughing about the bucolic picture thanks John!
Dick Gower


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