Early DG Rebuild Issue.

[maxstu]

Might as well clear a few shelves pending return of a 2.1 shortblock from Mr (Silverbullet) Holman.

So l decided to put together an early DG sitting in parts and taking up room. l used this as a donkey engine for 5k in late 2021 when rebuilding another DJ2.1.

Before fitting in 2021 l gave the DG a top end refresh with new piston rings, new fire rings and top/bottom sleeve seals and water jackets.
This time l have gone deeper and hand polished the cam and crank and fitted new standard bearings to both. The conrods are still okay on the top bushes, and nothing out of shape so new big ends were fitted, too.

On assembly l tested mating of cam and crank in half case in reverse. No jumping from the cam. All good so far.

Then tested with both cases and a few case bolts hand tightened. Engine glide around nice and smooth.

Applied green curil to case half and closed engine. M8 nut by tappet bores tightened to intially 15nm. M10 tightened to 25nm. Still rotating smoothly.

Final torques to 20nm for M8's and 35nm for M10 nuts (4 inside case with yellow sealant)
Now very difficult to turn by hand. And, on rotating, l can hear a faint scuffing sound in case around the captured bearing by crankshaft drive.

Time to take it apart? Your views please.

Regards,
Stuart

[maxstu]

Answering my own issue (the above was a draft from yesterday) l left the cases undertightened overnight.

This morning l gave it a few revolutions back and forth. Very smooth. Went up to correct torques 20nm and 36nm for early case nuts and still (but firm) silky smooth in both directions.

I cleaned the four internal nuts and replaced sealant.



That will do for me.

[silverbullet]

It goes to show how important it is to torque everything correctly. The case would have been preloaded when the crank tunnel was bored, but then heat cycling during use can cause some stresses that manifest themselves as misalignment or distortion when unclamped.
Glad you got it sorted, I'll be chasing the engine shop for your DJ crankshaft next week.

[Stesaw]

Mr fancy pants with building engines

[maxstu]

It goes to show how important it is to torque everything correctly. The case would have been preloaded when the crank tunnel was bored, but then heat cycling during use can cause some stresses that manifest themselves as misalignment or distortion when unclamped.
Glad you got it sorted, I'll be chasing the engine shop for your DJ crankshaft next week.

That is interesting reading. Many thanks for the information. And update on crankshaft, too.

[maxstu]

Mr fancy pants with building engines

Silverbullet or ajsimmo have absolutely nothing to worry about!



However, after the DJ, another DG rebuild will be on the cards.

[maxstu]

Back on this early DG rebuild.

Fitted sleeves and pistons today. New black and green seals, and fire rings with a dab of Hylomar blue...





Have push rod & tubes ready. Head nuts cleaned and washed with meths. Same for head threads. And yellow goo ready.



Jackets ready. Opened up grey elring grey Dirko HT for heads and jackets. Grey? Is this same as black Dirko? Never used grey before. Is it appropriate for T3 heads?

Regards
Stuart

[Stesaw]

Yeah the grey can be used on the head seals stu.
Same stuff for sealing the case halves.

[maxstu]

Many thanks, Steve.

[maxstu]

And another question...
This is effectively a donkey engine lm rebuilding on a reduced economy. But it is with new bearings and shells, etc. However the head nuts are suffering springback due to wear l suspect; but I'm not going to change anything now.
Using my Clarke Pro digital torque wrench l can see up to 18nm (from final setting of 50nm) springback of head nuts, leaving some at just 32nm tension.
What can l do to reduce head nut springback?
I've taken the nuts to 50nm three times and held at torque for ten seconds. Yet they still springback to between 42 and 32nm.
Regards
Stuart

[silverbullet]

Re-tap the nuts with a second or plug tap. The studs are probably bottoming out on the last thread.

If (?) its been rebuilt before some of the studs may have moved/backed out a little. Occasionally I have found a case with the studs installed not so tight and so the installed length can be variable.

[cobblers]

Perhaps temporarily try some washers under the nuts to see if that solves the problem, then you'll know you're bottoming out.

[maxstu]

Thanks to both for your replies and information.
Tried a couple of washers under one nut with same problem.
Went back to basics and cleaned out same nut thread again. This time using brake cleaner instead of meths. Cleaned mating surfaces on nut and cylinder head with brake cleaner, too.
Added NEW yellow goo and tightened it through three (pointless really as seven nuts are still in place) stages. 25nm, 40nm, then to 50nm with good results.
Poor cleaning regime (and using old yellow goo?) seems to be the culprit.
Will report back on the next seven nuts.

[maxstu]

All eight nuts re-torqued to spec with minimum springback.
I put a tippex spot on the socket to watch for reverse movement.



Nice spread of sealant.



Now to the other side with more care!

[maxstu]

On to other side, 3 & 4 cylinders, with extra care this time.
Upping my game when prepping and cleaning.
These nuts were previously cleaned. But not vigorously enough, it seems. and l don't think using meths as a degreasing agent cuts the mustard. Either pure alcohol or clutch/brake cleaner from now on.

More tomorrow.