The Unofficial Mamod and Other Steam Forum

TheOperative

Hi folks,

My 2008 Jensen 75 is a lot louder and runs much less smoothly than my 196? Jensen 75. I know I have posted about this before but I have done some investigation which may help others with the same problems.

The major sources of the noise in this engine are in fact two loose joint, one at either end of the conrod. The hole in the conrod at the crank pin is worn over-size and out of round, or at least I believe so. There is lots of slop and lateral play in this joint. Similarly, the conrod end in the piston rod fork also exhibits lots of both lateral and longitudinal play.

My very quiet and smooth running 196? exhibits ZERO play at the fork end and very little at the crank pin.

Disassembly and analysis of the 2008:

I removed the piston assembly and carefully ground off the head on the brass rivet at the piston rod fork. Then I gently popped out the rivet with a drift punch and removed the conrod. Very easy operation by the way.

The brass pin shows some signs of wear. The corresponding hole in the conrod seems alright, but the hole at the crank end is definitely worn oblong.

When I compared the 2008 conrod to the 196? They appeared to be exactly the same thickness; unfortunately, I do not have a dial caliper or micrometer. HOWEVER, the piston rod fork slot on the 2008 was cut wider than the slot on the 196? Hence, the lateral slop.

In any case, I have ordered two new conrods from Jensen so let’s see how they stack up with the original. I will address the slop in the fork with a shim or something upon reassembly.

Upon further analysis on the 2008, I noticed that the vertical location of the piston rod elbow joint center line seemed low. I measured the distance from the engine motor base to the center of the hole in the fork: 24 mm (running position). It appears to be 1 mm below centerline of the pistion rod.

I rotated the fork 180 degrees and measured again 25 mm but centered on the piston rod. If I reassemble it this way I will need to run in the engine again as the piston binds in this position.

So, this offset, plus the slop in the joints may be the reason the engine runs better in on direction than the other no matter how much I tinker with the position of the eccentric……

Sorry, no pictures. My €140 chinese-made Kodak camera took a dive after just 6 months….I am still looking for the receipt. I will try to post some later.

Hope this helps those who are interested.

T.O.

ozsteamdemon · Posted: Thu Jun 25, 2009 12:40 pm Post subject:

A good analytical approach to trouble shooting there T.O.

Good luck with your repair work .
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TheOperative · Posted: Thu Jun 25, 2009 12:51 pm Post subject:

metalhead100 · Posted: Thu Jun 25, 2009 9:29 pm Post subject:

Spinning the piston 180 in a wore in bore is not a good idea....

The bore and piston are run in to eachother.....flipping this relationship can cause severe leaks IF the bore and piston wore a bit funny.

Just a heads up.....say your piston was egged just a bit...but wore in now to fit the bore ect......when flipped it will re-wear the now NEW tight spot...then you will end up with major slop.

Worst case here but possible.

I battle slop with Teflon on my Wilescos .005 sheet works great to roll bearing inserts out of...Some Wilescos .005 fits without drilling the parts!

Jim
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rangerssteamtoys · Posted: Thu Jun 25, 2009 9:38 pm Post subject:

Jensens can sometimes on the loud side, but its not as loud and annoying as wilescos

I took some teflon tape and just wrapped a super thin layer around my shaft on my 25. Did the same with the con. rod, mine was so loose it just slipped right in no drilling or anything. OK I'm going to stop typing now because this post sounds pretty bad

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BK · Posted: Thu Jun 25, 2009 9:49 pm Post subject:

Gotta agree about not turning the piston 180 degrees.
Normally I reassemble with the piston in the smoothest running position.
Top report, I'll have to check my pins too, one of mine is noisey, and I've been blaming the stevenson link, it's got a loose pin.
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BK

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igy569 · Posted: Fri Jun 26, 2009 1:14 am Post subject:

Both of my Jensen 25's have a bit of play. The Wilescos are indeed the worst. Even after Jim fixed my D21, it still hase major slop at the crank. I am going to take it one step further, and sleeve it with a bit of brass tube. I think Jim can attest to the extreme wear for a 1 year old engine!

My Jensen 65, however, is very quiet. No slop at all! Go figure.
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rangerssteamtoys · Posted: Fri Jun 26, 2009 1:35 am Post subject:

TheOperative · Posted: Fri Jun 26, 2009 7:50 am Post subject:

Thanks for all the responses gents.

Forgive my temporary insanity: a run-in piston should NOT be flipped 180 degrees…..I thought about it shortly after I posted it and realized my error but just let it ride. Once run-in, piston and cylinder become a matched set, basic metallurgy. It is only natural to look for the fastest, easiest fix first but this is seldom the best fix.

Had I the tooling I could drill the hole over-size, on center, then install a new wrist pin but I don’t. I may very carefully try to bend the fork up 1 mm with the rod pushed all the way in the cylinder. However, I will run the engine first after the joint repairs to see if it’s necessary.

In any case, any engine run under load will experience wear.

On full size or model engines that copy them, the rod joints have replaceable bearing surfaces of lead, bronze or brass. Plus, each joint often had some kind of oil reservoir to keep the bearing constantly wet, thus the metal out of contact by floating on the oil. Finally, the area of the bearing need to carry the expected load was calculated or realized by trial-and-error, or simply over-built.

In a toy engine the bearing surface is usually the rod itself, there are no replaceable “bearings”, there is no provision for constant oiling, and some of us run them loaded for extended periods. Both my 2008 Jensen 75 and my Wilesco D18 have been run many times fully load with multiple workshops AND generators with multiple LEDs/lights…

Yes my 196? was constructed with no slop, but I doubt it was ever run loaded for extended periods, same for my nearly zero slop Wilesco D16. Both of these engine run exceptionally quiet to where one can hear the drive bands whizzing!

In all fairness, when you consider it, these little toy engines were only meant to run for 15-20 minutes at a time on a single charge of Esbit, pulling a few tools. Even the Jensen 100 5-tool workshop is very light and easy to turn, my D6E will run it easily.

So, where do we end up?

Conclusions:

I would strongly recommend any new Jensen/Wilesco/Mamod, etc. owner carefully examine his new engine for slop BEFORE firing it up. There should be nearly zero slop in conrod joints both lateral AND in the plane of the joint. Test it on air if possible, it should run VERY quietly at reasonable speeds both unloaded and with one workshop (not full blast).

If slop is found, return the engine for another one, or at least the sloppy parts for exchange. Jensen at least will have no problem rectifying the situ, they are very helpful.

A new engine should not clatter period, no excuses.

(NOTE: for Jensens, loose joints in the Stevenson reverse gear are not a factor since they run under very little load. My 2008 actually has tighter joints here than the 196?.)

For those that wish to load the piss out of their engines like me and run them for hours, you will probably need to mod the bearings as suggested, with Teflon or sleeves, etc.

Finally, consider using the smallest pulley on then engine and a faster spin when pulling heavy loads as this will also reduce the pressure on the joints.

T.O.

TheOperative · Posted: Wed Jul 01, 2009 3:32 pm Post subject:

Hi Gents,

A little update here:

I received the spares from Jensen. In short, I installed a new connecting rod with a new brass wrist-pin at the piston rod fork and a new crank bolt as well.

Before assembly however I closed the fork gap slightly and very gently using pliers. Then I straightened out the new con rod to insure the two ends holes were square, as it was slightly bowed from the factory. Finally, I very gently bent up the fork ½ mm to bring the hole in line with the piston rod. I did this operation with the piston pushed full in to avoid bowing the piston rod.

I installed the new conrod into the fork and after gently taping down the wrist-pin on either side, there is now ZERO play in the conrod/piston rod joint! The joint was slightly stiff naturally, but I greased the faces before assembly so no worries. Additionally, the crankpin joint has nearly no play as well.

These two joints are now as tight as the on the 196? Jensen 75.

I re-lubed all the joints and fired here up, letting her spin both ways for a good ½ hour before tinkering much.

RESULTS:

The 2008 Jensen 75 runs much quieter with out the annoying clatter, but still not as smooth or quiet as the 196? and seems to take a couple more PSI and more effort to spin.

The newer 75 also seems to vibrate a more for some reason I have not figured out yet.

I’ve tried balancing the 2008 engine to get it to run approximately the same speed in either direction and it is definitely more controllable than before, but still seems to favor one direction over the other. It also runs smoother in one direction than the other. The smooth running direction depends on which side of dead center the eccentric is positioned, odd.

In any case, one can definitely hear the unloaded engine puffing now and all the other mechanical noises that were hidden before by the clatter/rod knock, so it has been worth the effort, no question. Who knows, it may smooth out more as the new part run in a bit.

Any comments or experiences greatly appreciated. I would love to get to the bottom of the vibration and other issues.

T.O.

rangerssteamtoys · Posted: Wed Jul 01, 2009 4:24 pm Post subject:

Glad you got it all figured out, those older engines just run better than the newer ones... better quality, I'm not saying that Jensen has poor quality now, but it could be improved.

Is the 196? a cast iron base engine?

I'm also assuming that the 2008 is the metal base 25, that would explain the vibrating.

My bearings on my pressed metal base 25 are quite loose, thats just due a long hard running by previous owners, I oil the H*** out of my engines.
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TheOperative · Posted: Wed Jul 01, 2009 8:45 pm Post subject: