AM 25 Diesel engine Liner

[Graham Williams 5Participant @grahamwilliams5]

[Graham Williams 5Participant @grahamwilliams5]

Anyone know where I can source a liner for an AM 25 model aircraft diesel engine? mine is wrecked and I can't dimension it to make another.

[john kennedy 1Participant @johnkennedy1]

Graham, You might be in luck,I seem to remember I have one of those lurking in my workshop somewhere. Wont be home til late tonight. Will have a look and let you know. John

[john kennedy 1Participant @johnkennedy1]

Graham, You're in luck. Will send you the whole engine if you PM me your address. John

[Graham Williams 5Participant @grahamwilliams5]

Thanks for that John, have sent you a PM.

Regards

Graham W

[Graham Williams 5Participant @grahamwilliams5]

Made a new liner and contra piston for the AM25, dimensionally following originals as to ports etc., came out well, honed bore came out at 0.565" (nominal is 9/16" and made piston to 0.563", compression is low when assembled and it doesn't want to run, can anyone suggest what would be the accepted liner/piston clearance on that diameter as I suspect I've given it to much clearance?

[john kennedy 1Participant @johnkennedy1]

Graham, The piston is far too slack for a bore that size. They need lapping together and a diesel really needs to pinch at the top of the stroke. Search on this site for Ramon Wilson who has made some ETAs and ED Racers. He explains lapping very well.http://www.model-engineer.co.uk/forums/postings.asp?th=37520

Or see http://modelenginenews.org/index.html

I've not tried it but heard a cast iron piston can be made to grow by heating and quenching.

John

Edited By john kennedy 1 on 26/03/2013 18:12:34

Edited By john kennedy 1 on 26/03/2013 18:13:33

[john kennedy 1Participant @johnkennedy1]

http://www.model-engineer.co.uk/forums/postings.asp?th=37520

Have a read through this. John

[JasonBModerator @jasonb]

This is a better version of how Ramon machines the contra piston to a press fit. as opposed to lapping in the piston

[Graham Williams 5Participant @grahamwilliams5]

Thanks again John.

Will read up from sites you suggest. Made the liner from cast iron with a steel piston as per a Seagull engine I made a while ago so went with that, wondering whether that was a good call !! The hone I used seemed aggressive which is why it went a couple of thou over nominal, 9/16", and it looked to me it would be easy to 'bell mouth' the liner without a lot of care, mine turned out ok though. Got some Laps on the way so will be easier ? to close up the tolerances and get a good finish and hopefully will try to get the pinch you're referring to , will start a new piston tomorrow.

Jason.

Contra Piston was made of steel and I made it to a tight press fit to the liner, I don't think any compression is leaking past that. Will take on board the article you pointed me towards.

Many thanks

Graham W

[JasonBModerator @jasonb]

Ah I read it that you were talking about the contra piston, in that case look at the previous couple of pages in the link I posted about lapping the liner and then lapping the piston to fit the liner.

J

[john kennedy 1Participant @johnkennedy1]

Graham, I think you will find a better combination for a high revving diesel is a steel liner, either EN8 or EN1A and a cast iron piston.

The seagull is a lovely engine but couldn't be more different to an AM..John

[Graham Williams 5Participant @grahamwilliams5]

Hi John.

Think I'll start again with both liner and piston and use the combination you suggest and I'll do a bit more research on what others may have done before I start in future! One good thing is that I modified a Woodruff Keyseat Cutter to mill the ports, and it did the job with no problems, was going to try to use a slitting saw but no sizes available (diameter wise) that would replicate the original liner.

Cheers

Graham W

[Graham Williams 5Participant @grahamwilliams5]

Finally got the AM25 running again after reading up on the various articles. Lapped the liner, made from a section of car half shaft slightly tapered, using an ACRO Lap sourced from the USA and a cast iron piston and c/piston. There seems a little blow by on the c/piston so will make another. Also made a new con-rod as there seemed a little looseness at TDC on the original. Will try to post a few pictures of the process if I can figure out how to get them off my fone. Thanks for all the advice, really chuffed.

Graham W

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