Engine rebuild update

[Paul Kelley]

Interesting Neil. My chains and sprockets weren't too bad but were over the 25,000 mile mark so decided to change them along with the other work. However, knowing about the butter sprocket issue, we decided on balance to retain the old sprockets as they were in good nick. I like the sound of the magnetic sump plug, will look one out. Paul

[Dean]

Where can you get a magnetic sump plug I would like to fit one

[flying farmer]

A few years ago I did a forum poll about timing chain failures ( put timing chain poll in the search box, it is a few down the list showing as Which broke first?)

Basically the chain snapping without warning is unusual, somewhere between 2/3 and 3/4 of breakages (depending whether you include the Dolomite or not) were caused by the jackshaft seizing first. A good quality chain may even shear the jackshaft dowel without breaking the chain and cause much less damage. The only certainty is that cheaper chains will stretch and cause even faster wear on the butter soft crank sprockets that are available these days.
All that metal that is lost from the sprockets has to go somewhere. It isn't all caught by the filter as some goes through the bypass valve which is why I now favour magnetic sump plugs.

Neil

[KOY 23]

I’ve heard that one before, but dismissed it as never heard of chains breaking, unless caused by seizure of another part.

[Bakdraft007]

When I changed my timing chain, I was told by the supplier that their experience of people coming back was that the German chains tended not to stretch but when they go old would snap with no warning, whereas the UK chains would stretch then make a distinctive noise and so you new you had to change it before any major damage occurred..

Have other people hear this and is it true?

Dave

[Dean]

Nice to hear you cracked it in the end Paul I had a similar experience as you mine was running hot when I bought it so I removed the heads ( they came off easy) and refitted, it ran loverly for the rest of the summer until the mot ran out and I fitted an oil pressure gauge and it had 0 on tick over, so bit the bullet and like you had everything done inc the work on the heads,

[Paul Kelley]

By way of an update from some of my previous postings, I thought I would share the key details from my engine rebuild. It started back in the first lockdown last March, when the timing seemed good to deal with the top end of my engine. Working with my trusted mechanics John and Chris at Old Forge Motors in Harrogate, I sourced all the necessary parts and they did the skilled stuff! Heads skimmed and polished, new valve gear, new timing chain kit using the German type. All good when put back together and it ran well throughout the summer and autumn, but with the oil pressure dropping slowly but surely. After various tests the inevitable conclusion had to be reached: the bottom end of the engine also needed addressing.

Hindsight is a wonderful thing and it would have been better to do the whole job in one go. But this way it provided us with another project during the winter and the associated lock-down. As before, I sourced the parts and Old Forge did most of the heavy lifting – literally this time as the engine had to come out. Drake Engine Re-manufacturers in Bradford (W. Yorks) did the rebore and sourced the bearings, pistons and rings at +40 thou, plus they balanced the crankshaft together with all the associated parts through to the clutch plate. Ah, the crankshaft. It turned out that mine was already at +60 thou so I had to find another. Paul McLaughlin at Stag Classics (Alton, Hants) came up trumps with a reground and toughened one he had out the back, complete with bearings. The jackshaft and water pump were fully checked and retained as they are both in good working order. A new (County) oil pump was fitted with the replacement spring.

Finally, I decided to ditch the Strombergs and fit Chris Spain’s Stagweber 38 conversion with the optional active breather system to better replicate the Stromberg crankcase vacuum set-up. I’ve been back on the road for about 6 weeks now and all is running really well. An initial oil leak was tracked down to hardened ‘half moon’ black end plugs under one of the rocker covers, so all four replaced and something we missed first time round. It runs smoother, with more power, and better economy although yet to be fully measured. The Stagweber conversion is a definite improvement, with better pick-up, idling and choke operation as well as better performance. Have just changed the oil and filter after 750 miles as a precaution – lots of new metal in there! Cost? Don’t ask, but less than I have been quoted before by a couple of the Stag specialists and it should be good for another 150,000 miles and see me out! Old Forge work on classic cars of all sorts and have rebuilt several Stag engines over the years. Parts came from various sources including James Paddock, Robsport, LD Parts, and Rimmers. Wherever possible I went for better quality options, e.g. timing chains and head gaskets.

Paul