Info required on Tern 6hp aka Terhi 6hp Valmet Finnish air cooled outboard

[EugeneB]

Hi all,
I'm restoring a 6hp air cooled short shaft outboard. It's marked 'TERN 6', however a plate within indicates that it's a Terhi 6 made in Finland by Valmet. On another thread it's also been correctly identified as having a Mahle piston and head. I've rebuilt her slowly from a bucket of bits and she is now going however I'm working in the dark regarding any background info.
Does anyone have any info on this engine? Or a dealer (or ex dealer) in the U.K. as I need the correct woodruff key for her and a suitable prop.
Thanks in advance!

 

[mrcrabs]

Re: Info required on Tern 6hp aka Terhi 6hp Valmet Finnish air cooled outboard

Hey Eugene,
I couldn't sleep so I'm up reading tonite and see that your having trouble shearing keys's. It would be nice just to see a pic of the flywheel and the crankshaft on your outboard, I would like to see what the damge is so far to give a better responce but I will start with what I know and how I have over come this problem in the past with the single cylinder tecumseh.
Generally when you shear a woodruff key you begin to damage the flwheel and the crankshaft taper to the point that they no longer match each other and wobble, what I do is to lap the two back together using some common valve lapping compound just setting the flywheel on the crank with out the key and rotate it in the same direction while puting some mild down force on it with the other hand and checking it often looking for a uniform dull finish on the crank, you may have to use some fine emory to knock down any score marks in the flywhee taper and on the crank first, but don't over do it.
Then clean it all really good, I always replace the tecumseh singles thin flywheel nut and lock washer with a new nut that is deeper and toque to the the correct spec+, on the tecumseh I do beleive its 35 ft Lb. this has always cured my inherited problems with woodruff keys.
Be extra careful not to over lap it in past the crank tapers shoulder.
Also I never use any thing but a common Tecumseh key, I don't know how hard they are but the do shear, I would also wonder about your timing setup at the start position.

 

[EugeneB]

Re: Info required on Tern 6hp aka Terhi 6hp Valmet Finnish air cooled outboard

Mrcrabs, thanks for that and I'll get photos on as soon as, however......it turns out I've been rather foolish!! Not knowing this engine and working in the dark regarding the design, I wrongly assumed that she was designed without a nut securing the flywheel to the crank and the crank ended flush with the flywheel! I assumed that the flywheel was firmly locked/hammered with aa drift onto the tapered crank over the woodruff key to hold everything in place. Close examination shows that the threaded part has been cut off flush to the top of the crank-so closely that it wasn't initially apparent. That explains the shearing of the woodruff key-no matter how tight I placed the flywheel on the crank and over the tightly hand filed key, it was still spinning when the engine started causing the shearing!
Good news though-I took it all to an engineer for advice and he stated that the Terhi/Tern is still good to go with a small modification: an 8mm tap into the top of the crank and a threaded stud put in place and a suitable nut on top to hold the flywheel down. It's either that or weld the flywheel onto the crank which is rather permanent!! I'm going to have to do as you suggest about the valve lapping paste to make sure all's ok too. I'm not going to give up on the old girl yet!
Thanks,
E.

 

[mralex1994]

Re: Info required on Tern 6hp aka Terhi 6hp Valmet Finnish air cooled outboard

I have just picked up one of these engines, Few things i need to know,
Whats the spark plug gap?
And what fuel mixture? 50:1? 20:1? I tried 20:1 but it was very oily and not firing i dunno if its because i havent replaced the plug (its been sat for 30 years in a garage its pristine inside!)
Also did anyone have a manual for it?

thanks
Alex

 

[JB]

Re: Info required on Tern 6hp aka Terhi 6hp Valmet Finnish air cooled outboard

Howdy.

Welcome to iboats.

It is not polite to hijack threads, Alex. That is what you have done here. A hijack is when you turn attention away from the original discussion to your new question.

You will get a lot more and quicker help if you start your own thread with your new questions.

Good luck.

 

[mralex1994]

Re: Info required on Tern 6hp aka Terhi 6hp Valmet Finnish air cooled outboard

i didnt hi-jack the thread,
i simply asked if they knew anything that could help, and if they had any help finding the manual. i opened up a new topic few days ago and got no answer, so i thought i'd ask on a thread that was already open about it.

alex.

 

[JB]

Re: Info required on Tern 6hp aka Terhi 6hp Valmet Finnish air cooled outboard

You did hijack the thread, alex. Please don't do that. Please also be attentive to Admin announcements, like the one at the top of this forum.


Announcement:
Help Tip: If you have a question that has not been answered to your satisfaction in the archives, it is always best to start a new thread of your own. By starting your own thread, you will receive the maximum number of views by forum members.

BradC-iboats (Administrator)

 

[EugeneB]

Re: Info required on Tern 6hp aka Terhi 6hp Valmet Finnish air cooled outboard

I have just picked up one of these engines, Few things i need to know,
Whats the spark plug gap?
And what fuel mixture? 50:1? 20:1? I tried 20:1 but it was very oily and not firing i dunno if its because i havent replaced the plug (its been sat for 30 years in a garage its pristine inside!)
Also did anyone have a manual for it?

thanks
Alex

Hi!!! I'm delighted that somone else has found one of these great air cooled outboards!!!! I think it's a credit to iboats that it puts admirers of these engines in touch!!!! Great website!! To answer your questions:
1. Spark plug gap - I scoured the net for hours for info on this and found nothing! I was working from no info at all with a defective plug. I cleaned around the contacts and coil beneath the flywheel without resetting anything and I set it for approx 30 thousandsth of an inch and held it against the engine casing and it sparked well. I left it at that.
2. Fuel mixture - this was a problem for me as I knew the engine was prob from the late 60's and I suspected that at that time that german two stroke engines (mahle head, mahle piston, bing carburettor=german) probably didn't run on 100:1, so I've ran her on 45:1 - On a 45:1 mix she starts just fine however she isn't running as smoothly as I'd like-she ticks over/idles ok and at full revs is great but in between those she is temperamental!! I'm a bit nervous about weakening the mix still further to smooth her out over the entire rev range as I don't want her to seize-altho I've stripped the head and piston and if she did seize it wouldn't be a problem putting her back together again (when I was restoring her I bought a 51mm piston ring for a husqvarna chainsaw and that fitted perfectly!!)


Please note that I've stripped this engine/carb/leg/modified a yamaha prop for her and cleaned or replaced every nut and bolt in her. Of all the air cooled engines I've worked on, I think this is the most simple and reliable I've ever seen-and I've seen alot!!
Owners manual - I can't find an owners manual at all. Apparently there's an old guy in Finland that was a worker in the factory-however apparently he doesnt speak any english so thats no help I'm afraid about a manual. I found a link to a website in danish that may have info on them but I don't speak any of the scandanavian languages so I'm at a loss. On a happy note tho - I obtained a husqvarna piston ring and the bing carb seems common enough so interchangeable parts should be ok with some care.

Please note that it's a credit to the quality of the engine and the manufacturers that a box of rusted parts can be taken, (particularly a really badly rusted small end), cleaned, re tapped a stud into a tapered crank and fitted all together and a 50 year old engine starts and ticks over happily!!

I hope you get yours up and running soon!!
Thanks,
EugeneB

 

[EugeneB]

Re: Info required on Tern 6hp aka Terhi 6hp Valmet Finnish air cooled outboard

Hi all for anyone that's interested I thought I'd update you all on the recent developments about the tern/terhi air cooled 6hp. After fitting the stud and securing the flywheel I thought I'd try to sort out the rough running problem.
The outboard has been sitting in the garage for several months now and not been touched. I previously ran her at about 45:1 petroil mixture and she ran somewhat roughly- so I mixed a 50:1 mix and gave a few pulls and she started. I was nervous in case the weaker mix caused her to seize but she ran even better!!! I let her run for approx 5 minutes and she revved more freely than ever. So I think I'll stick to 50:1 due to potential seizure issues.
There's a slight cough before she increases revs but it's so slight that it's barely noticeable so hopefully a boat test will disperse my doubts!!! I tightened a few nuts and bolts after that MAY have loosened slightly (can't remember if they were dead tight to start with) so I wonder if 'locktite' or some other thread lock would be appropriate, altho I don't want to be struggling with an unmoveable nut a mile or two out at sea if she stops suddenly!! lol.
More to follow...................

ps - 1. new spark plug and shear pin en route
2. no owners manual yet

 

[Red Herring]

Re: Info required on Tern 6hp aka Terhi 6hp Valmet Finnish air cooled outboard

I'm located in Helsinki and my other mother tongue is finnish, so if you need something translated just let me know! Terhi is a well known brand up here and I think they used to be the market leaders in local sold powerboats.

 

[EugeneB]

Re: Info required on Tern 6hp aka Terhi 6hp Valmet Finnish air cooled outboard

I'm located in Helsinki and my other mother tongue is finnish, so if you need something translated just let me know! Terhi is a well known brand up here and I think they used to be the market leaders in local sold powerboats.

Hi Red Herring!! Thank you very much fr your help. I still have the Terhi outboard. I can't find an owners manual so I have a lot of questions to ask about the engine. What proportion do I mix the petrol and oil? How old is it? Is there a company/business in Finland that sells parts?

Thanks,

Eugene

 

[Red Herring]

Re: Info required on Tern 6hp aka Terhi 6hp Valmet Finnish air cooled outboard

I'll be glad to help, if you've got a photo of it that might be good. I'll see what I can find off the bat.

 

[Red Herring]

Re: Info required on Tern 6hp aka Terhi 6hp Valmet Finnish air cooled outboard

Found an email to someone at a swedish company that apparently knows a lot about the engines. gutafnordenswan (at) yahoo.se

These guys at least used to sell Terhi spark plugs: http://www.ngk.se/templates/ngkPage.aspx?id=251

http://www.elisanet.fi/voimakone/ Here you'll get a bunch of different parts. They're apparently closed until the 28.10, can't find a valid email atm. I'll let you know when I find it.

It's the same engine as a Terhi 5hp, I've got a bunch of links to some articles about the engine back from the 70's. Reading them will cost something, and I'm not sure if it really helps you. But let me know if you want them (all in finnish unfortunately).

 

[EugeneB]

Re: Info required on Tern 6hp aka Terhi 6hp Valmet Finnish air cooled outboard

Hi Red Herring - sorry I didnt get back to you but I've had to set the Tern to one side. I started it up today tho and she still goes fine!! I'll post photos by end of the week. (Currently working on a volvo 2hp). Thanks again for your help, EugeneB.