W116 280SEL engine reco / replacement

1973-1980 : 280S, 280SE, 280SEL, 300SD, 350SE, 350SEL, 450SE, 450SEL, 450SEL 6.9
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tyrrellnick
B Class
Posts: 22
Joined: Tue 17 Jan, 2017 2:22 pm
Model you own: w116

W116 280SEL engine reco / replacement

Post by tyrrellnick » Tue 17 Jan, 2017 3:45 pm

Hi all, putting this out there for your expert wisdom, advice, general good-natured feedback!

I picked up a really nice example of a '76 280SEL for a grand. Relatively new shocks, great body, no rust, really well looked after interior etc etc. Now, the problem is this: I think the rings are shot. I get to that conclusion by the following:

* running rough particularly at low revs, worse when engine is warm
* checked plugs, cables, distributor cap etc - strong spark
* pressure test each cylinder, results: c1 110psi, c2 85psi, c3 115psi, c4 60psi, c5 110psi, c6 105psi
* wet-tested cylinder 4, compression jumped to 140psi

I'm not a mechanic, but I like solving problems! An expert suggested to me valve clearance adjustment could solve the problem, but I'm not certain about this if I think about the result from wet-testing cylinder 4. Does this sound right to you?

Finally, if it is the valve clearances, then PHEW! But I'm prepared for the worst. If it's not valve clearances, then it's rebuild time. I've been told on these M110 engines that's a b!tch of a job, a good couple of days' work for a professional. So do you think I should try sourcing an M116 or M117 V8 to drop in there? How much work would be involved in that? As much as an engine reco?

Looking forward to your thoughts. I really just bought the car for cruising up and down the highway (I'm 50km out of Canberra in Australia), so I'm not too worried about having a perfect stock car, but I don't want to modify or spend too much. What's my least worst option here, do you think?

Cheers!

CraigB
OZBENZ Admin
Posts: 4760
Joined: Thu 23 Jun, 2005 2:18 pm
Model you own: I own multiple different models
Location: Hawthorndene (Adelaide)

Re: W116 280SEL engine reco / replacement

Post by CraigB » Tue 17 Jan, 2017 3:55 pm

I think you are spot on with your analysis. Myself i would be looking for a rusty running car with the 280 engine and swap it in, or buy an engine if you can trust the seller. The tricky part is removing the head so even if the valves were leaking chances are you need to do the head. For the V8 conversion you will need to do wiring etc and would probably best to have a donor car if going that way, sounds like heaps of work and cost to me compared to getting another M110 and bolting it in. Just my opinion - see what others say.
Craig Baulderstone
Lurch
280s's
280SE3.5
280SL
350SL
500SEC's
560SEL's

tyrrellnick
B Class
Posts: 22
Joined: Tue 17 Jan, 2017 2:22 pm
Model you own: w116

Re: W116 280SEL engine reco / replacement

Post by tyrrellnick » Tue 17 Jan, 2017 4:16 pm

CraigB wrote:I think you are spot on with your analysis. Myself i would be looking for a rusty running car with the 280 engine and swap it in, or buy an engine if you can trust the seller. The tricky part is removing the head so even if the valves were leaking chances are you need to do the head. For the V8 conversion you will need to do wiring etc and would probably best to have a donor car if going that way, sounds like heaps of work and cost to me compared to getting another M110 and bolting it in. Just my opinion - see what others say.
Thanks Craig. I'm thinking I can pop some oil thickening agent in temporarily to get the compression back up to where it'll fire the low cylinders. I've got a local antique car club where I live which is pretty active, I MAY be able to convince one of the blokes to do a project, but even if I can I can't decide whether to replace the engine with a V8 or rebuild the current one. Probably a similar amount of work, I imagine? I suppose at least if I rebuild the 2.8 I'll at least know it's done and will be reliable...

CraigB
OZBENZ Admin
Posts: 4760
Joined: Thu 23 Jun, 2005 2:18 pm
Model you own: I own multiple different models
Location: Hawthorndene (Adelaide)

Re: W116 280SEL engine reco / replacement

Post by CraigB » Tue 17 Jan, 2017 4:48 pm

you could give it a go but to be that low my guess would be broken ring/s and could be damaging the bore - but then could have been like that for ages. Can always resleeve a cylinder if you can't hone out. If bores worn throughout it is not the rebore cost but the new o/s piston cost that would be scarey. Sometimes you can find good secondhand o/s pistons, but these are really robust motors and although I haven't pulled a lot down, i have pulled down quite a few 3.5 v8s and all were still on original bores and pistons. If you go through and add up all the parts you might get a bit of a shock even if you can find someone to do a freebie on the rebuild.

Anyway that was the basis of my suggestion that if you scan through adds there used to be lots of cheap W116 280 cars. You have the skills to put a battery in and do a wet/dry compression check and really thats all that matters. Except maybe stem seals, but then if you can drive it and it doesn't blow smoke on start up and can coast down a hill and then hit the accelerator and no smoke then you know thats ok. If your car is running then you have parts from your injection/ignition etc.

And that was my point, that i reckon is the easy cheap road - rebuilding a motor if you need to pay someone last time i heard was 6 or 8k. You can check out some parts prices at precision international if you google that. V8 you are starting from scratch and need the motor ignition everything to be good and then you need to wire it etc, may need different tailshaft, rego checks issues potentially.... but if your keen go for it. Unless prices have jumped probably cheaper to just buy another V8 if thats what you really want.

and make sure if you do any replacing if your car is d jet or k jet, although you can possibly just change the motor and bolt all your stuff back on it.
Craig Baulderstone
Lurch
280s's
280SE3.5
280SL
350SL
500SEC's
560SEL's

tyrrellnick
B Class
Posts: 22
Joined: Tue 17 Jan, 2017 2:22 pm
Model you own: w116

Re: W116 280SEL engine reco / replacement

Post by tyrrellnick » Tue 17 Jan, 2017 4:57 pm

CraigB wrote:you could give it a go but to be that low my guess would be broken ring/s and could be damaging the bore - but then could have been like that for ages. Can always resleeve a cylinder if you can't hone out. If bores worn throughout it is not the rebore cost but the new o/s piston cost that would be scarey. Sometimes you can find good secondhand o/s pistons, but these are really robust motors and although I haven't pulled a lot down, i have pulled down quite a few 3.5 v8s and all were still on original bores and pistons. If you go through and add up all the parts you might get a bit of a shock even if you can find someone to do a freebie on the rebuild.

Anyway that was the basis of my suggestion that if you scan through adds there used to be lots of cheap W116 280 cars. You have the skills to put a battery in and do a wet/dry compression check and really thats all that matters. Except maybe stem seals, but then if you can drive it and it doesn't blow smoke on start up and can coast down a hill and then hit the accelerator and no smoke then you know thats ok. If your car is running then you have parts from your injection/ignition etc.

And that was my point, that i reckon is the easy cheap road - rebuilding a motor if you need to pay someone last time i heard was 6 or 8k. You can check out some parts prices at precision international if you google that. V8 you are starting from scratch and need the motor ignition everything to be good and then you need to wire it etc, may need different tailshaft, rego checks issues potentially.... but if your keen go for it. Unless prices have jumped probably cheaper to just buy another V8 if thats what you really want.

and make sure if you do any replacing if your car is d jet or k jet, although you can possibly just change the motor and bolt all your stuff back on it.
Wow, $6-8k for a $1k car would not be a smart way to spend my money! But yes, you're probably right, finding another M110 engine lying around would be the cheapest/easiest option. Still a bit of mucking around, but all the other bits and pieces seem to be in good condition. Don't seem to be any M110's around at the moment though, unfortunately.

PS. If I was to replace it with a V8 from the same family, what re-wiring would I have to do? Assuming I could find an engine with injection system etc to accompany...

CraigB
OZBENZ Admin
Posts: 4760
Joined: Thu 23 Jun, 2005 2:18 pm
Model you own: I own multiple different models
Location: Hawthorndene (Adelaide)

Re: W116 280SEL engine reco / replacement

Post by CraigB » Tue 17 Jan, 2017 5:46 pm

You could try the forum sponsor - number at top of board index page since you are around Canberra. Cars do come up though if you keep your eyes open. And maybe put an advert in the wanted parts bit.

Short answer re wiring is i really don't know. You need to find a V8 car and have a good look under the bonnet, take lots of photos and compare to yours.

And over the next few days see what responses you get.
Craig Baulderstone
Lurch
280s's
280SE3.5
280SL
350SL
500SEC's
560SEL's

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