4.2 sump on a 3.8 engine.

[abowie]

Can I put a 4.2 sump on a 3.8 block?
What do I have to modify to do this?

[44DHR]

Andrew,
We have covered this subject a few times and the key is the diameter dimension on the rear oil seal housing.
Hopefully this helps :- viewtopic.php?f=7&t=8988&p=70083#p70083
Regards,
Dave

[abowie]

Thanks for that Dave; a lot of helpful info there.

I currently have a 3.8 engine with no sump.

I ordered and received a replacement sump from one of the usuals, by the part no C16750. Unfortunately what they sent me was the sump off one of the British army tank "crate" engines that had had the rear seal surface machined to mimic the 3.8 sump. The problem with this sump is that I don't know what baffle it needs to fit it, whether the 3.8 oil pickup will work or if I need to convert it to 4.2 pipes, whether the 3.8 dipstick will read correctly (the sump is a different capacity. Finally, the sump is recessed at both the front and the rear and so it looks wrong too.

I have several 4.2 sumps and a couple of seal housings from 4.2 engines, so I should be able to fit the sump to my 3.8 block.

My concerns are, in addition to the above potential problems, whether the 3.8 crank is the same as the 4.2 crank in terms of the section at the back where the seal fits. I don't currently have a 4.2 crank to compare to.

As I see it my options are:

1. Fit a 4.2 sump with 4.2 seal housing if it fits the 3.8 crank properly. This is the easiest option.
2. Machine the rear seal facing on a 4.2 sump to fit the 3.8 seal housing. This is what has been done on the tank sump that I received.
3. Source a 3.8 sump. best solution from the originality and function viewpoint, but not easy to find.

Any suggestions?

[44DHR]

Andrew,
Sorry, for the delay in response.
I believe both the 3.8 and 4.2 sumps use the same Sump Baffle Plate Assembly, (Part number C16741). The Photo 1 below show a nice clean 3.8 sump with one fitted and the next Photo 2 an oily 4.2 sump and the baffles are the same. Depending on the age of the 3.8, the only difference is that the bolted in filter basket was changed about June 1962 to have 4 semi circular cutouts as been in the final Photo 5.

The other major difference between the 3.8 and the 4.2 is that the later 4.2 has a larger uprated oil pump with a larger oil pick up pipe into the basket, from 11/16 inch to 3/4 inch, so that would need fitting if the later pump is fitted, but the basic layout and clamping of the pipes is the same in the sumps. The main difference is that the 3.8 Sump has a bigger diameter cast into the rear of the sump and although as you say you could fit the smaller 4.2 Seal Cover Housing to suit the smaller cast diameter 4.2 sump, the other difference is the 4.2 by having a more improved double lip rubber seal against the sump - rather than the single flat cork gasket on the 3.8, the side profile is extended as can been seen on Photos 3 and 4. Photo 3 shows 3.8 sump on a 4.2 crank - which it will not seal and Photo 4 shows the correct 4.2 sump on the same 4.2 crank which it now seals by being the correct smaller cast diameter and having a longer length longitudinally. By changing the Seal Cover Housing, this would require the Crank rope oil seal to be re-sized and all the potential issues that could give.











Incidentally both these 3.8 and 4.2 sumps were ribbed, whereas the very early 3.8 sumps had smooth sides.

I trust this assists,
Dave

[abowie]

Exactly what I needed to know Dave. You're a bloody champion!