Hymac 690

[Jeremy Rowland]

Latest update, after many years of wondering about this machines details, I have finally been able to identify it through the engine number, the machine was new to Bybrooke Plant on 03/01/1974
Back to the business of this engine strip down and rebuild; I couldn't really do anything until I had measured the cylinder bores, before I go on more it is my suspicion that this engine had a heat seizure and somebody did a quick cheap rebuild on it, according to the Perkins manual the liners should measure 98.48mm to 98.50mm quite a tight tolerance in my opinion, I used a set of telescopic gauges and then measured with an external micrometer, the readings went from 98.45mm to 98.54mm, readings were taken from top, middle and bottom of the liners along with one diagonally opposed measurement of each liner.
There was some minor scoring in the bores, one of which I had wondered if it was a crack as it ran above the travel level of the top ring, I did get a second opinion on this but after honing was happy that it was only a score mark, that was on no6 cylinder.
The block liners were honed, I also checked the big ends which are standard, I will probably fit new pistons and rings along with big ends and a full gasket set.

Jeremy

[Jeremy Rowland]

Today's visit was cut short by the weather, but I still made some progress although I am eager to get this machine back into some sort of order, I must first concentrate on getting the engine right.
I have ordered six new pistons and ring sets, plus a set of big end shells and a full gasket set; today's plan was simple fit the new pistons to the con-rods, the old pistons needed heating up a little to free the gudgeon pins, once done the new pistons and pins were fitted with ease, making sure the arrow points to the front of the engine with the big end bearing tabs towards the camshaft side of the engine.
Plenty of time was taken doing this, so no rush!

Jeremy

[Jeremy Rowland]

Went up today with a plan which turned into a fail checked new piston ring gaps all okay fitted the rings to no1 piston okay came to fit the big end shells and
Oh well I'll get them swapped; at least I got some other work on the machine done.

Jeremy

[Jeremy Rowland]

Armed with the correct set of big end bearings I finally managed to get the pistons back into the lump.

Jeremy

[essexpete]

Jeremy, a rude question, how much was the overhaul kit?

[Jeremy Rowland]

Jeremy, a rude question, how much was the overhaul kit?

Good question Pete; the cost did change as some of the parts supplied were incorrect (although the cost of those was refunded) the whole lot cost me £414.28 inc VAT
That was for 6 pistons, 6 ring sets, six sets of conrod big end bolts and nuts, a set of big end shells plus the top and bottom end gasket sets. The only issues I had was the top gasket set was the wrong one but they sent me the correct one FOC, and the big end bearing shells which I had an issue sourcing some new ones, even Perkins have not made these since 2014.
I used a good company called Emmark UK Ltd who are genuine and very helpful, as I said the only thing they could not supply was the correct big end bearing shells, I think I eventually got them from a website of a Sheffield based company 'parts for engines' they were more expensive but was the only place where I could find any big end shells.

Jeremy

[essexpete]

What is the under sump clearance like for working?

[Jeremy Rowland]

What is the under sump clearance like for working?

Very poor TBH it would have been a better plan to take the whole lump out in some ways, however that would also have led to other problems so I've managed to get it done the hard way.

Jeremy

[Jeremy Rowland]

I managed to get up there yesterday; there was one job on my 'tick list' that had got to be done.............. fit the sump back onto the engine. One thing with rebuilds is that it always takes much longer to fit things back together as parts need cleaning, and the sump was no exception to this. Although I had drained the oil prior to stripping the lump, in the bottom of the sump was about an inch of oil sludge, looks like this engine has been well cared for not!
I strung the sump up to drain out and started the clean down with some old mucky derv which I had drained off the machines fuel tank, this was finished with some brake cleaner, job done. Next was cleaning the oil pick up which was also mucky and jammed full of oily sludge. Once that had been stripped and cleaned I set about scraping off the old sump gasket from the sump and bottom of the engine block.
Finally the time to refit came, needless to say and cutting a long story short it's a right pig of a job, I stuck the gasket to the sump, maneuvered it into place, then crammed my hand between the sump and block, just enough room to get the pickup assembly back in and awkwardly fit its gasket and bolt it back to the lump before finally raising the sump and bolting it back into position.
I do have to get a few new bolts but that aside job done.

Jeremy

[Matchless?58]

I am so jealous of those shiny new pistons! That's going to run lovely when you have finished sorting it out.