Force - assessing wear

[AJS]

I have now sucseeded in taking my Force engine apart and need some
words of wisdom on which bits to replace? The engine would run, then
eventually simply stop. Last thing was that I simpy could not get it
started, despite trying several glowplugs.

Well now it's in bits and before I spend my cash on a new engine, or
indeed a box of expensive bits, I thought I'd ask a question regarding
the wear of the engine? The piston appears a nice fit in the liner,
without evidence of scratches, etc, although I'm not sure what
constitutes a worn piston/liner combination, as clearly when hot, the
situation may be quite different.

What worrys me more is that the conrod shows quite a lot of play on
the crakshaft - in fact I wondered if this was the cause of the engine
stopping? So as the least expensive replacement part, I'm thinking of
replacing it, anyone any thoughts/advice on this?

Otherwise, it's onto a new piston set, including liner, but then I am
near to a replacement engine.

Advice?

[M78Ultra]

If your sure its the connecting rod thats worn and not the crankshaft I
would get that part and then send the motor off for a recrimp job.
There are several good people on eBay that do this and it works pretty good
and is cheap if your on a budget.
(Had several friends have this done with worn motors and they worked well)
You could try just the new connecting rod before you send it off as well and
see if it rids the problem.

"AJS" <skipp@ntlworld.com> wrote in message
news:62f1e58e.0409261400.714ed5c0@posting.google.c om...
> I have now sucseeded in taking my Force engine apart and need some
> words of wisdom on which bits to replace? The engine would run, then
> eventually simply stop. Last thing was that I simpy could not get it
> started, despite trying several glowplugs.
>
> Well now it's in bits and before I spend my cash on a new engine, or
> indeed a box of expensive bits, I thought I'd ask a question regarding
> the wear of the engine? The piston appears a nice fit in the liner,
> without evidence of scratches, etc, although I'm not sure what
> constitutes a worn piston/liner combination, as clearly when hot, the
> situation may be quite different.
>
> What worrys me more is that the conrod shows quite a lot of play on
> the crakshaft - in fact I wondered if this was the cause of the engine
> stopping? So as the least expensive replacement part, I'm thinking of
> replacing it, anyone any thoughts/advice on this?
>
> Otherwise, it's onto a new piston set, including liner, but then I am
> near to a replacement engine.
>
> Advice?

[Jim Banks]

M78Ultra wrote:
> If your sure its the connecting rod thats worn and not the crankshaft
> I would get that part and then send the motor off for a recrimp job.
> There are several good people on eBay that do this and it works
> pretty good and is cheap if your on a budget.
> (Had several friends have this done with worn motors and they worked
> well) You could try just the new connecting rod before you send it
> off as well and see if it rids the problem.
>

I had never heard of a "recrimp" job, so I went to Ebay, did a search,
and came up empty-handed. Is there another name this service goes by?

--
Jim
-----
www.onandaga.com

[mike]

Just an observation on piston/liner wear. I've read and heard loads of
opinions on how to judge a good fit, and diagnosing wear marks etc.

In the late seventies through to the early 80's I was into a sport called
FAI Combat which involved .15 sized aircraft engines. One of my favourites
was one called a "Cox Conquest", pretty much a clone of the Italian Rossi.

The Cox had a shocking (and partly deserved) reputation for mech failures,
in my experience mostly around the front bearing. Anyway, to get to the
point (at last:-) during FAI combat it was very common for the motors to run
lean toward the end of the "tank" because the tank was a pressurised bladder
which could minutely lose pressure toward the end. My Conquest pistons would
routinely have awful looking black scorch marks running from the crown to
skirt, typically worse around the exhaust port area. People would look at
them and shake their heads. They would turn them over and comment on the
(lack of) compression. People would snigger and sneer, Rossi and Nelson
owners would stand in small groups muttering to each other .... OK not
really, but you get the picture - my piston/liners would be simply discarded
by most people.

But with the (increasingly tricky) job of starting accomplished, the jaws
would drop. Those engines would simply *scream* - the performance was
completely off the scale (for the time), low (ok, almost non existent)
compression notwithstanding. Or indeed, maybe *because* of the low
compression. I didn't know (or care).

So, I say to you, the *only* metric for piston/liner wear is performance,
pure and simple:-)

Mike


"AJS" <skipp@ntlworld.com> wrote in message
news:62f1e58e.0409261400.714ed5c0@posting.google.c om...

> The piston appears a nice fit in the liner,
> although I'm not sure what
> constitutes a worn piston/liner combination

[Nigel Mellor]

"Jim Banks" <banks_jimNOSPAM@hotmail.com> wrote in message
news:2rph8jF1c9dbvU1@uni-berlin.de...
> I had never heard of a "recrimp" job, so I went to Ebay, did a search,
> and came up empty-handed. Is there another name this service goes by?

The process is known as "pinching". The liner is pressed into a tapered die,
stretching it vertically and reducing the bore at the same time. The
dimensional changes are less than a thousandth of an inch but are sufficient
to restore compression in a worn liner.

The main exponent of this art goes by the name of "os rocket" on eBay.

[Nigel Mellor]

"AJS" <skipp@ntlworld.com> wrote in message
news:62f1e58e.0409261400.714ed5c0@posting.google.c om...
>I have now sucseeded in taking my Force engine apart and need some
> words of wisdom on which bits to replace? The engine would run, then
> eventually simply stop. Last thing was that I simpy could not get it
> started, despite trying several glowplugs.
>
> Well now it's in bits and before I spend my cash on a new engine, or
> indeed a box of expensive bits, I thought I'd ask a question regarding
> the wear of the engine? The piston appears a nice fit in the liner,
> without evidence of scratches, etc, although I'm not sure what
> constitutes a worn piston/liner combination, as clearly when hot, the
> situation may be quite different.
>
> What worrys me more is that the conrod shows quite a lot of play on
> the crakshaft - in fact I wondered if this was the cause of the engine
> stopping? So as the least expensive replacement part, I'm thinking of
> replacing it, anyone any thoughts/advice on this?
>
> Otherwise, it's onto a new piston set, including liner, but then I am
> near to a replacement engine.
>
> Advice?

Did the engine stop when hot and idling? Flame-out on idle and difficulty in
starting can be caused by very lean LSN settings. Richen the LSN and HSN and
make sure the carb is properly primed before starting.

With the glow plug in place and tightened down, do you feel any resistance
when turning the engine over by hand?
Drop a few drops of after-run oil down the glow plug hole and then refit and
tighten down the glow-plug. Is there any more resistance when turning the
engine over by hand and can you hear the "pop" in the exhaust as the engine
goes over TDC?

[AJS]

"Nigel Mellor" <nigel.mellor@reply-to.in.signature> wrote in message news:<cj8u5m$ae1$1@newsreaderg1.core.theplanet.net>...
> "AJS" <skipp@ntlworld.com> wrote in message
> news:62f1e58e.0409261400.714ed5c0@posting.google.c om...
> >I have now sucseeded in taking my Force engine apart and need some
> > words of wisdom on which bits to replace? The engine would run, then
> > eventually simply stop. Last thing was that I simpy could not get it
> > started, despite trying several glowplugs.
> >
> > Well now it's in bits and before I spend my cash on a new engine, or
> > indeed a box of expensive bits, I thought I'd ask a question regarding
> > the wear of the engine? The piston appears a nice fit in the liner,
> > without evidence of scratches, etc, although I'm not sure what
> > constitutes a worn piston/liner combination, as clearly when hot, the
> > situation may be quite different.
> >
> > What worrys me more is that the conrod shows quite a lot of play on
> > the crakshaft - in fact I wondered if this was the cause of the engine
> > stopping? So as the least expensive replacement part, I'm thinking of
> > replacing it, anyone any thoughts/advice on this?
> >
> > Otherwise, it's onto a new piston set, including liner, but then I am
> > near to a replacement engine.
> >
> > Advice?
>
> Did the engine stop when hot and idling? Flame-out on idle and difficulty in
> starting can be caused by very lean LSN settings. Richen the LSN and HSN and
> make sure the carb is properly primed before starting.
>
> With the glow plug in place and tightened down, do you feel any resistance
> when turning the engine over by hand?
> Drop a few drops of after-run oil down the glow plug hole and then refit and
> tighten down the glow-plug. Is there any more resistance when turning the
> engine over by hand and can you hear the "pop" in the exhaust as the engine
> goes over TDC?

The engine did run ok for a while, it appeared to get quite hot, then
after a few minutes it would simply stop at idle, normally with a bit
of a clunk. I tried to richen the mixture starting with the "manual"
setting, but still pretty much the same. The reason I dismantled the
engine was that the thing simply got to the stage that it would not
start at all, not even at the "manual" setting. As far as compression,
the thing appears hard to turn over when it stalled, which suggested
to me that a) it was perhaps too rich, but then why was it so hot and
b) that the compression was OK, and I'm pretty sure that the "pop" you
describe was there. However now the engine is in bits, I really did
not expect to see so much play on the conrod to crankshaft bearing and
figure this could be the cause of the problem, possibly together with
say a leaky engine. I plan to get a new conrod, but then am worried
that the crankshaft could be the worn bit, although with this steel
and the conrod bearing soft metal, I would expect it to be the conrod.
Once I have this, I was going to re-assemble, using sealent on the
relavent parts and fingers crossed the thing would run again. The rest
of the engine looks OK, there is no discolouration of the metal
indicating extreme heat. So I still think that the new conrod might do
the trick.

[Nigel Mellor]

"AJS" <skipp@ntlworld.com> wrote in message
news:62f1e58e.0409280507.21535234@posting.google.c om...
> The engine did run ok for a while, it appeared to get quite hot, then
> after a few minutes it would simply stop at idle, normally with a bit
> of a clunk. I tried to richen the mixture starting with the "manual"
> setting, but still pretty much the same. The reason I dismantled the
> engine was that the thing simply got to the stage that it would not
> start at all, not even at the "manual" setting. As far as compression,
> the thing appears hard to turn over when it stalled, which suggested
> to me that a) it was perhaps too rich, but then why was it so hot and
> b) that the compression was OK, and I'm pretty sure that the "pop" you
> describe was there. However now the engine is in bits, I really did
> not expect to see so much play on the conrod to crankshaft bearing and
> figure this could be the cause of the problem, possibly together with
> say a leaky engine. I plan to get a new conrod, but then am worried
> that the crankshaft could be the worn bit, although with this steel
> and the conrod bearing soft metal, I would expect it to be the conrod.
> Once I have this, I was going to re-assemble, using sealent on the
> relavent parts and fingers crossed the thing would run again. The rest
> of the engine looks OK, there is no discolouration of the metal
> indicating extreme heat. So I still think that the new conrod might do
> the trick.

It sounds to me like the engine has adequate compression and is indeed running
too lean and overheating.

If adjusting the needles will not help then you most likely have an air leak
somewhere. Use a small amount of high temperature RTV sealant to seal the
backplate to the rear of the block and also around the carburettor neck where it
fits into the front of the block. Some PTFE tape wrapped around the LSN threads
may also help.