Nemett Lynx 15 cc 4 Stroke I/C Petrol Engine

[Swifty]

Gus, I would do as you mentioned in an earlier post, use a 48mm PCD for the holes, allowing for the 7mm dia screw heads, the smallest size across the screw heads will be 41mm, this gives you 0.5mm clearance per side. The outside size across the screw heads will be 55mm, the same as the outside dia of the cylinder. The screws won't hang over the outside and it will look OK.

Paul.

 

[gus]

Gus I measured the heads on some M4 cap head screws last night and they were just under 7mm so you may just be able to use them without having to resort to other methods to hold the cylinder on. As you have not drilled the holes yet I would move them out to to a 47.5mm PCD which will place them in the middle of the flange and give the screw heads a bit of clearance to the 40mm waist.

Drawings show the head at 28.75, not whats on your height gauge.

Thanks for the alert.
I must change my specs. Where did I get 28.50? Looks like will have to make adjustment somewhere to makeup. I have surplus to cut one more Outer-head if necessary.

I thought I had 28.75 but somehow it became 28.5 after my wife in to admire the Outer-Head.

 

[Brian Rupnow]

Gus---If you HAVE TO do it---You wouldn't be the first person to turn the heads down a few thou. in diameter on socket head cap-screws.---Brian

 

[Swifty]

For the home hobbyist, modifiying screw heads would be OK as a last resort. When I had a toolroom, anybody who attempted to modify a standard screw was told in no uncertain terms that it was not on, it makes maintenance a real pain.

Paul.

 

[gus]

Hi Brian,Paul.

When I was building Production Machines,I sure hate to introduce or do non-standard stuff. The Indian Ingersoll-Rand Air Compressors came in with different A/F Hex bolts that require 2 AF Spanners to loosen. They were not to SAE and not Grade 5. Was a nightmare.

Just rechecked,Think I get away w/o turning socket heads.

 

[Jasonb]

If it is a bit tight the ones with the smooth heads are a usually fraction smaller than the ones with the straight knurl around the edge

 

[gus]

There is so much details on the Outerhead and machining never seems to end and have O/H totally done.:wall:
At least,I did not wreck O/H with the last cut.
For this week, that's all Gus will do. Its weekend fishhhhhhiiing.
Next week cut the inclined face to take spark plug, the inlet and exhaust ports.

 

[Brian Rupnow]

Guys--We are not building production machinery here. It will probably never have to be maintained in our lifetime. If turning a screw head saves a part which has a lot of work put into it, then go for it. I'm not a novice in the industrial arts. This has been my life for half a century. I KNOW that anyone who used a non standard or modified fastener would be staked out on an ant hill and left to die by the head of engineering!! But come on---It's a model for Gods sake. In model building you do whatever you have to do, and the only person you have to be responsible to is you.---Brian

 

[Swifty]

I also mentioned that it is OK for the home hobbyist, just threw the other bit in for general interest.

Paul.

 

[doubletop]

Thanks for the alert.
I have surplus to cut one more Outer-head if necessary.

So hang on to it for now. I ended up doing two heads. However, at the point I knew I'd have to start again I kept going on the first one to prove all my setups and approach without worrying too much if I stuffed it up. The second one was way faster to make as I wasn't freaking out worrying if I was doing it the right way.

Pete

 

[doubletop]

Guys--We are not building production machinery here. It will probably never have to be maintained in our lifetime. If turning a screw head saves a part which has a lot of work put into it, then go for it. I'm not a novice in the industrial arts. This has been my life for half a century. I KNOW that anyone who used a non standard or modified fastener would be staked out on an ant hill and left to die by the head of engineering!! But come on---It's a model for Gods sake. In model building you do whatever you have to do, and the only person you have to be responsible to is you.---Brian

I'm with Brian on this. We started this thread with a debate on fits. If it fits (properly) its the right size. It not like you are making a batch and all the parts need to be interchangeable. If something breaks you aren't going down to the stores for a new one, you are going to make it yourself, so it fits....

Pete

 

[Brian Rupnow]

Whoops!!! Didn't mean to start any kind of peeing contest here. I respect Swifty and think he is a super craftsman. (after all, he did build my engine). Us old farts who have worked around machinery all our lives know there are some things that you just DON'T DO. We also know that we have a lot more leeway on model engines that are in all respects "One offs" and probably will never require maintenance in the way real industrial parts do.----Brian

 

[capin]

Gus, it might have been a pain to do but You have got it licked now. I also have this on my list to do. Your doing great job! Brian

 

[gus]

I just made a brand new paper weight. Cut the wrong side. Three days of hard work gone down the drain.:wall::hDe:
On the brighter side the next O/H will be best piece after a practice run.

May 20th 5pm.
OK . No more paper weight. Took my hobby problem to bed.
Outer-head reworked. Put in a locktited plug spark plug hole. New hole for spark plug.
Prefer to use Champion 10mm plug so as to standardise on plug. Fuel/air intake port and exhaust port to done later.

It's fishiiiiiiing tomorrow.
Day after will start work on crankcase.

 

[Swifty]

That's a bummer Gus, it doesn't help either when they mirror image the picture on the front of the magazine, very confusing. Just noticed that I left out a tapped hole on my crankcase, the one for the belt idler, but that's an easy fix.

Paul.

 

[gus]

That's a bummer Gus, it doesn't help either when they mirror image the picture on the front of the magazine, very confusing. Just noticed that I left out a tapped hole on my crankcase, the one for the belt idler, but that's an easy fix.

Paul.

Hi Paul,
I just discovered the reversed mirror image foto.
Believe I can save the out-head by plugging up the spark plug hole. But also debating making a new piece.

Good luck with the other parts.

 

[gus]

Was able to cut the 25 degrees bevel corner of outer-head. The DIY arbor and bought out slitting saw from ArcEuro came in very handy and beats end milling. The Electronic Device to set angle certainly helped. Surprise.Surprise. Made in Singapore.Bought it year ago.Cost me a bomb. Checked accuracy on a 45 degree Set Square.

 

[gus]

Started work on the crankcase. The Vertical DIY BandSaw is an asset.If not,Gus would be panting away cutting the 2 1/2 '' square blank.
Facing the blank and milling the sides was man's job for a baby lathe and mill. At last the cylinder and outer-head have a crankcase to stand on. For smooth finishing,always use a new end mill.
Come tomorrow the crankcase cavity gets done. More like a tunnelling job from Singapore to reach Paul in Australia. Too much metal to remove.
Not fishing tomorrow as the ebb tide current brings little feeding fish and the rain today will kill all chances of landing good size fish.

 

[doubletop]

Gus

You are going well there. As per the write up drill the corners, bore the two large holes and then there's very little left to remove with the mill. I used a T slot cutter and was amazed how quickly it all came out. I subbed out the block for the Bobcat to a mate with CNC and it took him six hours to do the crank case. I think start to finish this one only took me about 4hrs

Pete

 

[gus]

Gus

You are going well there. As per the write up drill the corners, bore the two large holes and then there's very little left to remove with the mill. I used a T slot cutter and was amazed how quickly it all came out. I subbed out the block for the Bobcat to a mate with CNC and it took him six hours to do the crank case. I think start to finish this one only took me about 4hrs

Pete

Hi Pete,
Thanks for standing by me. Just the cavity took total of 8 hours. Using tee slot mill did not come into my head though I did use it for the Rotary Table Slots. The mini mill had to be coaxed to do the excavation.Am sure glad I did not destroy it with the last cut. Took lotsa tea breaks and pee breaks to recuperate.