Volfy

My Feedback: (23)

I am trying to change out the connecting rod in my MVVS 26cc glow engine. I got to removing the cylinder liner and it is stuck in there really good. I tried penetrant oil and the usual trick of sticking a popsicle into the exhaust port and push up with the piston. Before I go heat up the cylinder with a propane torch, I figure I'd better ask here to see if there is anything particular I need to do.

Help?

DarZeelon

Volfi,


Make sure your wife is not at home and heat her cooking oven to 275-300°F.

Put the whole assembly in the oven for 10-15 minutes.

Use hot-gloves, or a thick rag, so you will not get scalded.
It will push out quite easily when hot, since the aluminium crankcase will expand more than the steel sleeve and will no longer grip it.

Volfy

My Feedback: (23)

Dar,

Thanks for the quick reply. I figured I had to heat it up. Oven will do it much more evenly than a torch. The kitchen oven is a no-no. I got my wrists slapped the last time I used it for 'non-food' purposes. It stunk up the house and I was told never to do it again. May be I can 'borrow' the toaster oven and do it in the garage...

BTW, I noticed the steel cylinder liner has a small notched machined on the top lip. I assume it is for alignment purpose. Is there an alignment pin or something there to match up with the notch? Or should I mark the spot before I remove the liner?

Thanks.

DarZeelon

Volfy,


You can mark it in the notch, but perfectly aligning the ports would be sufficient as well.

The piston-ring is pinned against rotation (the pin is recessed) and the gap must go between two specific ports in the sleeve.

It should not be too much of a problem.

pe reivers

This is how I do it, provided the liner is not fried (coked)
fit a propeller
remove back cover and carb
remove cylinder head
insert popsicle into exhaust port with piston at bottom centre
clamp engine mounting flange in vice
heat the case with a heat gun whilst slightly torquing the prop <slightly!>
After some time, the liner will budge and move up enough to present an edge
remove posicle from exhaust ort
grab the liner edge with padded pliers, and still heating the case, pull the liner out.
Take care not to twist the liner, or the ring may catch in the ports.

The notch is 1mm. before liner removal, drill a hole about 5mm deep in the case, through the notch. When re-assembling the liner, place the shank of the drill in the hole, and use it to guide the liner down. It will now be in exact the same position as it was before.

Have a nice day after a job well done.

If your liner is coked and will not budge, you just found the reason for the rod failure. Insufficient engine cooling, wrong oil or both.
In this case you may need a special tool that can apply a lot more force when the case is heated. In fact so much force that it approaches the limits of what the crankcase will endure. to make this tool you need a lathe, drill press, round stock, thread spindles and 8mm metal sheet.
At the end, your day may not be so nice. Mouth edges drool, and gray hairs appear at the temples, if not already there.

Volfy

My Feedback: (23)

Pe,

Thanks for the very comprehensive instructions. Between yours and Dar's, I should do just fine. Great tip on the drill bit guide, BTW.

Mine is actually a brand new MVVS 1.60 glow. I am just swapping out the bushed conrod with a needle bearing version, so I can run less oil and possibly convert to gasoline. I bought 3 of these engines. Sold the first one with the CMP Extra 72" it was mounted on. Great runner and plenty of power.

pe reivers

I beg you, don't.
the oil/fuel mix in glow fuel is not suitable for the needle bearings, and you soon will have an engine failure. Though not advised by the MVVS factory, use of ST fuel with 10% oil in the bronze bushed engines will do fine, provided you keep the engine cool.

Volfy

My Feedback: (23)

Hmm... maybe I'll just skip right ahead and do the full gas ignition conversion then.

My Zenoah G23 glow and several weedie conversion engines run just fine on 90% methanol 5% castor 5% nitomethane. After every flight session, I do drench/slosh the crankcase with afterrun oil (50/50 air tool oil & ATF) and pour the milky mix out of the exhaust though - same as I do with all my glow engines.

I like the extra power boost with methanol on the small conversion "gassers", but I view them as almost disposable. The MVVS 26cc is a jewel by comparison. So if it might do damage, I'd rather not rick it.

pe reivers

the MVVS 26 is built in a small package, and delivers the power of a 40cc weedy, so they cannot be compared. The bearing load in MVVS is pretty high.