View Full Version : HOw many times can you rebuild an engine?

26th Nov 2002, 11:29
Is there a limit on the number times you rebuild these old recips?

Will there come a time when the snarl of Merlin will live on only recordings?

You want it when?
28th Nov 2002, 15:13
I don't think there isan actual limit to how often you can rebuild a piston engine. Each time you replace parts with either old new stock or get it re-manufactured.

Biggest stumble I guess might be the block but these are rarely machined just cleaned.

Lu Zuckerman
28th Nov 2002, 15:40
I can’t provide the number of times but I can provide those elements that do have limitations.

Cranks can be reground to the next oversize bearing up to the point where the largest bearing available has been used. It may be possible to replate the crank after grinding to get back to the original size bearing but only after the crank has passed several NDT procedures and, If allowed by the manufacturer.

In most crankcases the cylinder hold down studs are held in place with Rosanne (Sp) Inserts and in some cases Helicoil inserts. In either case when an insert must be changed some of the metal holding the insert must be removed and the next size insert is installed. Most manufacturers will provide the necessary “meat” in the casting to allow as many as three or four insert replacements.

Cylinders can be bored out several times. With each rebore the base of the cylinder is painted to indicate to the mechanic what level of rebore or, the new oversize of the cylinder. During the initial build of the Sikorsky S-58, H-34, HSS-1 helicopters many of the cylinders on the “new” R-1820-84 engines had orange paint on the cylinder bases indicating that they were at the maximum for rebore. If the cylinder had to be replaced a new cylinder and piston had to be installed.

The crankcases must also be able to pass several NDT procedures before being reinstalled on the engine however the manufacturer may place a life limit on the crankcases as well as the rotating parts of the engine assembly to include camshafts. Normally at overhaul all bearings are replaced.


28th Nov 2002, 20:28
............A bit like George Washington's axe in the Smithsonian Museum. When asked if it really WAS the authentic article, the assurance was given that it was - accepting that the shaft had been replaced several times and the head had certainly been renewed at least once, but it was definitely the original axe !

I think it's much the same with an engine - and indeed an aeroplane - as long as you hang onto the original maker's name and data plate.

29th Nov 2002, 03:38

Dont know about R1820 but on most engines orange base means chrome plated bore and DO not use chromed rings.

:) :)

Lu Zuckerman
29th Nov 2002, 12:58
To: Got the T Shirt

It seems that I chose the wrong person to ask. While working on a training program at Sikorsky in the engine installation section I asked one of the lead techs what the orange ring indicated and he told me what I had stated in my post.



29th Nov 2002, 23:05
I don't think there is a life limit on the engine data plate! :D :D :D

That's usually the only original part after a couple of overhauls!

An orange ring on the cylinder base indicates Chrome bore.

1st Dec 2002, 11:57
Thanks for the interesting replies.

It's a real privilege being able to talk to the pros.....

big pistons forever
1st Dec 2002, 23:53
You would be surprised how many old engine parts are still out there, particularly for round engines. I know of a recent T-28 rebuild for a (very) rich American doctor. He specified that every part in the CW R1820 engine had to be brand new. It took a bit of digging but the engine shop sourced everything, and he got his wish.

Lu Zuckerman
2nd Dec 2002, 00:09
About six years ago I was given a tour of a company in Everett, Washington that specialized in overhauling big round engines mainly R-2800s. They told me that P&W Canada bought up all surplus new cylinders and sold them to operators and overhaul facilities. When the supply ran down they started to produce new cylinders for most P&W engines. They also told me that the pistons for these engines were being manufactured under license by a firm in South America.


2nd Dec 2002, 23:05
Next time you hear the delightful hiss of a rotary at Old Warden just remember that they need an overhaul after 5 hours or so.

A trip behind the scenes is an Alladins cave of boxes marked '110 leRhone' etc.

These cores are more than 80 years old. Anybody priveledged to see the innards of one of the old rotaries can only marvel at the craftsmanship. They are jewels.


6th Dec 2002, 00:13
Props are about the same. I remember some years ago we had a prop due O/H from Britain's Revenge on the Empire, a Bongo Van (P-BN Islander). The blades were inside min specs and there was a mandatory hub change.

When the prop came back from O/H it had the original Ser No and Log Book - the rest was new.

How do you get more grunt from a turbine? Well, if it's a PW120, for around US$65,000 you get a new data plate, use your own screwdriver and - presto - a 100 SHP increase in grunt!

I think the cheapest flat six engine overhaul I ever saw was in an (unnamed) Asian country. $10 for two cans of Dulux spray enamel!

Most worrying engine overhaul? A reman engine in a C150 (operated over very hostile tropical jungle) had zero oil pressure on three separate flights. Eventually the problem was traced back to a small amount of residual glass beads in an oil gallery in the crank case. A bead would float free and hold the pressure relief valve open.

Seems some versions of the venerable Lycoming 540 are having more than their share of problems. There's some interesting AD's being published and interesting theories floating around regarding a double catastrophic failure in a Chieftan in Australia, resulting in an overwater fatal accident.

6th Dec 2002, 22:44
The word "overhaul" is the catch !!

Most manufacturer have a specification for parts that have to be replaced to qualify the engine for "overhaul" and all engines are not excatly the same.

Fo many parts there are oversize limits and in some cases replateing to bring pack to standard

In my dim and distant past overhauls on big radial R1830 and R2800 were already becoming a problem for parts.
We would initially specify a mimimum number or reworks for various parts ( cylinders and pistons) but as time went on that went by the board.

The Prezetel is a Pratt copy built in eastern bloc so they are making some new parts !

7th Dec 2002, 07:26
G'Day Reg.

What's a Prezetel? (Not up on Eastern blok engines.)

I thought the Walter was the closest to a PT6A (but not the same and parts aren't interchangeable). Also heard Pratt's took a slice of Walter and some Pratt parts are now made there.

Walter seems very cost effective and popular. I saw a Glassair a couple of weeks ago with an 800 HP Walter up front!

7th Dec 2002, 18:06
Hi Torres,

The engine is made by PZL in Poland.
There are some of their engines flying in the USA on the Vargas and some crop sprayers.

If you do a Web search on PZL Poland you will see they make a lot of stuff under licence.
(from both the USA and Russia:) :) )

I have worked on their copy of the P&W R985 - seemed to work Ok :D