6 cylinder engine rebuild questions
 

Hi everyone I'm Chuck and am totally restoring my 1970 914-6. I have the engine pulled and am tearing it down including opening up the case. I want to increase the displacement size since I have to replace a lot of the parts any way .I was wondering if its worth it to replace the crank and connecting rods to 70 mm and rebuild to 2.4 specs with 84mm pistons or keep the original crank and build to 2,2 l specs. Do you feel it would reduce the value of the care by making it not totally stock? I also heard that you can pot on 90mm pistons&cylinders keeping the same crank and increase the displacement to 2.5L What are your thoughts ?

I would contact Henry at Supertech; he and a few others on our forum are definitely experts on what to do to that case to get the most reliable performance while keeping it happy and healthy. If it is a numbers matching engine to the car, I would likely keep it appearing stock but would not hesitate to strengthen the internals and up it to a 2.4. I know if I had the original case for my original '71 914-6, that is how I would approach it. Since I do not, I have a '95 3.6 in her. Good luck. Michael

Thanks Cairo for the super quick reply I do have a matching number 914-6 and Ive had a gut feeling that going up to a 2.4 would be OK especially with the original mag case. I will defiantly contact Henry for some advice .Thanks again.

Yes, going to 2.4 is definitely possible .. but will this build the type of engine you want. Short stroke engines in a light car have a unique character. If it was me, I’d be tempted to build a higher compression short stroke 2.3 or 2.5 using 86.7, 87.5, 89 or 90mm Nickies & JE pistons. I think 87.5 & larger may require boring the case registers .. Standard 2.2 registers are 92mm from memory. Keeping the case standard would have some appeal for me …

I'm with Rosco , short stroke ! Boring the case can be reversed by Ollies E & R , I've done this numerous times .

If it's a numbers-matching car, I would leave the case alone and either build a short stroke engine, or buy a 3.0+ engine for more displacement and durability.

Going to 2.4L with 84mm pistons and a 70mm crank/rods is a popular upgrade. It's a great balance of power and reliability. However, modifying the engine may affect the car's originality and value. The 2.5L option with 90mm pistons and cylinders is also possible, but it's a more extensive and expensive modification.

Truthfully, there is very little in a 914/6 engine long block that is conducive to a performance build.
The block is fragile
The crank is a boat anchor
The valve size is minuscule as is the dome configuration
The oil pump needs to be replaced for better oil flow
The cams can't be upgraded without welding...yikes.
If you clean it up you can make a great man cave coffee table.

My recommendation is to strip to the valve covers and pickle the core. Save it for matching numbers value and find another long-block.
I would look for a core with a 7R case. That would mean a 70.4 crank.
I like using 2.7 cores in 914/6 projects because the flywheel is a direct fit.
When you have a 7R core, then you start asking the relevant questions.
One of the best engines I've had in my 914/6 was a RS spec 2.7 with Solex cams.
Enough power to have a great ride and yet not so much that you need to fit a front cooler.
Good luck with you project.


http://forums.pelicanparts.com/uploa...1741974027.jpg

I'll second what Henry has to say. I have the 2.7 motor Henry alludes to in my /6. It is a lot of fun and very tractable. The original number matching is sitting on the shelf. I added a cooler in back for a little extra oil capacity and dropped temps about 10* so that even on the hottest of minnesota days it still isn't over 220*.

Thanks Everyone for your reply Im fairly new to posting. And thanks Henery for your input and engine table pic.I showed it to my wife and the first thing she said ways "that guy is not married." I have a high school friend who's a bike enthusiast he owns 13 bikes including a 1913 Indian that actually runs and he keeps 4 of his bikes in his family room and yes he is not married. seriously though I think I'll go for the 2.4 build I'm really attached to the car Ive had it since the mid 70"s I'm 71 and not into performance like I was when I was younger( there's no places you can drive fast any more). I want to keep it close to original . The 2.4 engine should give me a big improvement over stock especially with hi compression pistons. Let me ask Im finding it hard to find a reasonable 70.4 crank any suggestions.And thank you all for your time and expertise .
Chuck.

Your question
 

So very hard to argue with Henry because he knows the drill…..but iI took a different tact.
To keep one engine, I went with the 2 liter case ( with updates) and stock crank. Add old school 2 liter Mahle S Pistons and cylinders. Then had original heads done with 46/40 valves plus flow. DC 30 cams and an upgraded oil pump. Henry’s rockers and modified sprockets. Ported intakes to match heads. Bosch distributor. Not yet running but already down the rabbit hole. The objective was to have a spirited street engine that seemed stock externally. Easy to second guess……
my only change would have been 2.2 heads for better chamber and valve angle….oh well. It is matching #.

Or he married the right woman…