Engine questions

[gagvanman]

I recently built a new 1776 engine from scratch:

New Aluminium Autolinea case
Stroke 69mm
Bore 90.5mm
Cylinder Head - CB performance 044 40 x 35.5mm valves
Solid Rocker Shafts
Standard 1:1 rockers
Camshaft Scat C35
Valve train geometry set with 60" rocker shims and shortened pushrods
Compression Ratio 7.5:1 set with 1mm barrel shims
SVDA Distributor

This is the first VW air cooled engine I have built, so I am no expert. All my knowledge gained from this forum and YouTube.

Engine goes well especially above 3000 revs, but is a bit lumpy at 30mph in 4th gear.
Tends to over heat (gets over 200 deg C) on long journeys. So have installed an external oil cooler. Yet to test the result of this.

However: further research has me questioning the 7.5:1 compression ratio. If I remove the barrel shims the ratio should come out at 8.2:1 with the clearance that I have. Would this bring the temp down?

Also would low down driveability be improved if I added 1:1.25 rockers?

Your thoughts appreciated.

 

[sparkywig]

Higher compression ratio means higher cylinder pressure which means higher cylinder temps. So no, it won't help bring the temp down.
That engine shouldn't get hot or run lumpy in any gear.
But running hot usually means the mixture is weak, check the timing and see what the condition of the spark plugs is? Have you had the carbs set up at all, rolling road usually gets them right.

 

[Bluesnailman]

John Muir says in a stock bus don't shift to 4th until 35mph minimum.



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[fallingoffalot]

Agree with JM, I don't shift to 4th until about 40-45mph. On the hottest day of the year, 19th July (I think) I went down to Newquay and when on the A30 hills my engine was running at about 125°C. It didn't seem to mind.

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[montypsx]

If it is juddery low down the rev range but takes off when you floor it try putting larger emulsion tubes in the carbs it will give it more fuel and make it drive better I just had a similar problem with mine. Also did you break it in at 2000rpm for 30mins?

My build was 1641cc full flowed 100cam new crank bearings with ported heads I also matched all cylinders so they were the same cc and put 34icts on it with iridium plugs and Petronix distributor. After I put the new emulsion tubes in I’m getting an extra 6-8 mpg on normal roads and is sooooo smooth

Hope this helps

 

[K@rlos]

That compression ratio is rather low for that cam, wants to be at about 8:1 to 8.5:1 for the cam to be the most happy. However that won’t reduce engine temps, strictly speaking a higher compression ratio will increase temps BUT if everything else is correct then 8.5:1 isn’t a concern in a bus motor. Ratio rockers increase cam lift & duration so will move the power band up the Rev range making low end driving worse. Plus you’ll need dual spring for them with that cam if you don’t have them now.

Missing a lot of info here…

What carbs do you have? What’s the jetting & vents sizes?
What’s the timing set too?
What exhaust do you have?

 

[K@rlos]

John Muir says in a stock bus don't shift to 4th until 35mph minimum.



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A 1776 isn’t a stock bus….

 

[gagvanman]

Thanks for all the comments, I never said it was a stock bus, but I will be mindful of the gear change \ speed.

Engine has twin ICT carbs with the following jetting:
idle jet 55
Main jet 160
Air corrector 180
Emulsion tube f6
Float jet 150
Huco 2.1psi electric fuel pump

SVDA dizzy with electronic ignition. Timing has been tested in the ranges 28-32 deg, engine runs like a dog at anything below 30, currently set at 32.
tried a couple of different type of spark plugs currently running NGK DE7A gapped at 26 thou.
Exhaust is 4 into 1 quiet pack.

Carbs have been balanced but I do think they may be running lean so have ordered a couple of size 57 idle jets. Montypsx, you mention changing the emulsion tubes, what size would you recommend?

 

[K@rlos]

Thanks for all the comments, I never said it was a stock bus, but I will be mindful of the gear change \ speed.

Engine has twin ICT carbs with the following jetting:
idle jet 55
Main jet 160
Air corrector 180
Emulsion tube f6
Float jet 150
Huco 2.1psi electric fuel pump

SVDA dizzy with electronic ignition. Timing has been tested in the ranges 28-32 deg, engine runs like a dog at anything below 30, currently set at 32.
tried a couple of different type of spark plugs currently running NGK DE7A gapped at 26 thou.
Exhaust is 4 into 1 quiet pack.

Carbs have been balanced but I do think they may be running lean so have ordered a couple of size 57 idle jets. Montypsx, you mention changing the emulsion tubes, what size would you recommend?

How are you setting the timing? At full advance or at idle ?

 

[Bluesnailman]

John Muir says in a stock bus don't shift to 4th until 35mph minimum.



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A 1776 isn’t a stock bus….

I know, but I didn't say it was stock either. but 30mph in 4th is a pretty low rpm, so was just suggesting that we might not expect it to pull particularly well at that speed. I'll leave it to the techies for more detailed analysis....

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[gagvanman]

Timing set at full advance

 

[K@rlos]

Timing set at full advance

You want it at 28-30 degrees at full advance with the pipe plugged.

 

[gagvanman]

I may not be an expert, but I do know that the vacuum advance pipe needs to be blocked when checking the timing. As stated previously engine ran like a dog below 30, and best results was at 32...

 

[K@rlos]

I may not be an expert, but I do know that the vacuum advance pipe needs to be blocked when checking the timing. As stated previously engine ran like a dog below 30, and best results was at 32...

Well you didn’t state thats how you’d done it so how was I suppose to know you did?.. Instead of throwing darts take it to a rolling road. They will dial all the fuelling in through out the Rev range and find which timing setting is optimal for the engine.

 

[gagvanman]

Long time since I threw any darts, so apologies if I have ruffled any feathers.
Thanks again for all your comments...

 

[ozziedog]

Forget about the darts for a minute guys, is it running any bettererer??? :shock: :shock:

Ozziedog,,,,,,,,, important stuff first :mrgreen:

 

[gagvanman]

Changed the idle jets for 57's, backed out the mixture screws 1/4 of a turn on both carbs. Seems to run a bit smoother on my drive, haven't had a chance to take the bus for an extended run yet. Also found out that the old girl has a single port cooling fan. Waiting for a twin port fan to arrive. Hopefully the combination of the 2 upgrades will result in a cooler running engine and can get a trip out before Crimble...

 

[67panel]

Personally I would take the shims out as that compression is a bit low for that cam and to my mind will improve low end pull. As to the get into 4th over 30 mph my 1600 single port bottom end with ported twin port heads ,ITCs and header pulls like a train from 25 mph in 4th!

 

[gagvanman]

If I can fix the overheating issue I do plan to reduce the deck height to increase the compression ratio and gain a few more horses. Probably in the new year sometime...