24 replies to this topic

[Paulryanmini]

Hi all
I just brought a new project.
84 mini which has been partially restored by the previous owner. 998 A plus

The engine was apparently rebuilt but is smoking very badly at idle and under load with the odd backfire

It will only run with full choke and gets bogged down under load .
Smoke is grey and leaves specs of oil on the back of the mini after a drive.
So far I've done the following

Compression test ,all ok
Checked plugs, look new but very black and sutty.
I've removed the head to check the gasket and it appears fine. No scoring in the bores but it may be glazed. I'm no expert on this.

Things I noted during removal of the head

Both inlet and exchast nuts were not overly tight.
Build up of soot on the 2 outer exahust ports and in the manifold.

Block and head appear flat (using a steel rule)

I'm odds on what to do next. I was tempted to swap out for a 1275 but prices are high at the moment and if I can get this engine working it will tide me over for a few months.

I have yet to remove the stem seals but I think if these were at fault you would only get smoke when you left your foot off?
Any advise appreciated
Thanks
Paul

[Paulryanmini]

Here is a link to pictures of the head and block

http://imgur.com/gallery/EZDqsS3

[gazza82]

Sounds more like the carb is badly adjusted. How long has it benn sitting as the fuel gums up if left a while.

I would also have done a compression test before stripping it down.

Edited by gazza82, 28 December 2018 - 02:24 PM.

[Paulryanmini]

Sounds more like the carb is badly adjusted. I would have done a compression test before stripping it down.

thanks for your reply. I did do a compression test prior to strip down. Which was ok. Carb was apparently rebuilt during engine rebuild, but I didn't try any adjustments

[cal844]

Sounds more like the carb is badly adjusted. I would have done a compression test before stripping it down.

thanks for your reply. I did do a compression test prior to strip down. Which was ok. Carb was apparently rebuilt during engine rebuild, but I didn't try any adjustments

What was the compression results?
Did you do the test with a small amount of oil in the bore?

How old is the fuel?

Personally I'd do the valve stem seals and relap the valves as you have the head off. Also replace the bypass hose(silicone or Kevlar type) and water pump if they look old

[Paulryanmini]

Thanks.
Results were 180-190ish.
I didn't try it with oil.I think as you said I'll change the valve stem seals. Refit the head and go from there. It's only £50 for a new gasket and studs. Luckily the bypass hose is the new silicone type

[Geordie Bob]

It could of been sucking in air if manifold nuts were loose so hence using full choke and making one side sooty.
Leak was probably on the other side.

[Paulryanmini]

Thanks for your reply.
Yes I'm starting to think it was just as simple as that, plus maybe some adjustments on the carb.
Going to order
New gasket set
New studs and nuts
Oil + filter
New spark plus
Coil and leads

I'll give it a go before I go down the engine replacement route

[nicklouse]

Check the valve guides.

[Paulryanmini]

Cheers nick, I'll check them once the new gasket arrives :) thanks

[Chris.Williams]

Sounds like carb settings and possibly the manifold leaking, nothing wrong with those compression numbers.
Also nothing wrong with being cautious and doing the head gasket, after all, it is a mini haha.

[Rorf]

Those bores look very glazed so I am very surprised you are getting those high compression readings. You mention the engine was recently built, did they just put new bearings and rings in as the top of the pistons look very dirty and carboned up, plus there is a slight ridge at the top of the cylinder. Never trust another persons rebuild unless he has an exemplary reputation in the engine building business.

[Paulryanmini]

Those bores look very glazed so I am very surprised you are getting those high compression readings. You mention the engine was recently built, did they just put new bearings and rings in as the top of the pistons look very dirty and carboned up, plus there is a slight ridge at the top of the cylinder. Never trust another persons rebuild unless he has an exemplary reputation in the engine building business.

Thanks for your reply. I have no paperwork on who did the engine rebuild as it was done by the previous owner. My long term plan is to replace the 998 with a 1275 or bigger. I’m more trying to get this engine going for practice before I replace it.

[ACDodd]

That's a bore washed re ring. Tear it apart there more problems inside.

Ac

[Paulryanmini]

Cheers guys. Time to find a 1275 or bigger engine so... No point pouring money into a 998