Amazon: HS6 slipping?

[Derek UK]

I was going to say mark the domes so you know where they are now, say F and B, and then swap just the domes over but you could also try swapping over the dampers as you say one is new. With the dampers in and oil up to level the drop speed of the dampers should be equal or very close. NEVER use anything abrasive on the inside of the domes. Gas or thinners only.

By old style do you mean the alloy inlet and 1 or 2 down-pipe cast exhaust? The best manifold is the cast iron one that was fitted to the '68 B20 which has no emission butterflies. You're lucky if you have one of these but worth keeping an open for if you don't.

[volvogv]

I pulled both dampers out and compared them. The old one and the new one are very different in their design. The new one is a simple 1 piece collar that goes against a cone tapered stop, but the old one has an extra ring that floats around. The new one is nice and close, no 1/4 inch free play before the fluid slows it down.

I swapped dampers and lifted the pistons. Aha! The free play problem followed the dampers.

Time to replace the other damper.........
Thank you all for your great suggestions!

BTW, I have the straight manifold with a cross tube and no butterflies.

Mike

[Ron Kwas]

Mike;

That 1/8" of free play is typical and normal...but the 1/4" of undamped free play on one Dashpot is not...it seems incorrectly high, and that difference in the Damping Valves obviously needs to be checked and resolved...they certainly want to be the nominally same.

"new one is a simple 1 piece collar that goes against a cone tapered stop, but the old one has an extra ring that floats around. The new one is nice and close, no 1/4 inch free play before the fluid slows it down. " I think the single piece one is missing that ring, but are you saying that is the one with the excessive free-play?...I wonder if there were variations in the valves or if you are missing the valve ring of one... I'm getting confused here...

In general...the brass components of the (one-way) Damping Valve are secured with a circlip, so the questionable one of yours may have been apart and not reassembled correctly or with the valving ring missing. Correct assembly of Damping Valve on rod is: Brass Valving Ring (cone towards mating cone of rod, flat toward Cylinder), Brass Cylinder, Circlip The valve components are free to float when assembled, but are (hopefully) always wet with damping oil, so should exhibit minimal wear.

"I wonder now if the piston bores are worn out from years up up and down motion against the dampers?" The is no contact between Dashpot and Dome inner wall!!! No wear is possible!! Only contact between Dome and Dashpot is at center precision tubes which are lubricated by the damper oil...so differences occur (see 5-7 Second Test at: http://www.sw-em.com/su_carbs.htm ), but major wear is unlikely.

My recommended procedure for servicing dome and dashpot (see also: http://www.sw-em.com/SU%20Carb%20Service.htm ):

Disassembly:
1. Remove Damper Valve, inspect, flush clean with carb cleaner, set aside.
2. Remove Dome screws, then lift and remove Dome gently in-line with dashpot axis. Clean inside surface of dome by flushing with carb cleaner, wipe with soft rag, flush/wipe inner tube ID, NEVER use abrasive of any kind on ANY of these components...EVER!!), set aside.
3. Remove Dashpot spring, flush, wipe clean, set aside.
4. Gently lift Dashpot from housing along its axis of travel (being careful not to apply any bending force to metering needle at ANY TIME during servicing), pour most of damping oil out of tube (waste), but pour a sample into clean rag/paper towel to inspect color, viscosity (especially if you don't know what might be in there), and for contamination/particulates.
5. Flush/wipe Dashpot, including inside tube, flush/wipe OD of Dashpot tube.

Reassembly is reverse of Disassembly as they say, but apply a film of ATF on OD of Dashpot tube, so it is nicely lubed when Dashpot is lowered over it.
When Dome is in-place and secured, check for smooth travel along entire range.
Lift Dashpot so that top of Dashpot tube is visible in Dome opening. Add Damping oil (ATF) to just below top of Dashpot tube, then lower Dashpot gently to bridge. Insert Damping Valve and snug black octo.
Recheck Dashpot travel, noting damping action now (after an initial small amount of free travel).

That's all I can think of for now...others can chime in if I forgot any major steps...

Good Hunting.

[Derek UK]

I would add that both springs should be the same length when hanging free.From Burlen - Red = Load at length 4.5 oz @ 2.635 in. No sure how you measure that! There is also more than one strength of spring but the Volvo ones should all be the same. Colour coded, Burlen says RED. AUC4387. Damper should be AUC8103. I didn't realise that there a whole bunch of these that look the same but have different dimensions to give different damping characteristics, at least that's what Burlen says. Looks to be well over a dozen different AUC numbers listed for dampers.

http://sucarb.co.uk/carbspec/carbure...pares/id/2595/

http://sucarb.co.uk/dampers-caps-oil...ssemblies.html

[Ron Kwas]

Mike;

Derek's info is confirmed by my reference source for SUs: Tuning SU Carburetters published by Speedsport

You might just check with Agent Strangelove (aka Chris Horn) on this side of the Atlantic, to see if he can supply one from an organ donor car.

Cheers from a snowy Connecticut!

[volvogv]

I just did some checking and the old damper with the extra ring with the 1/4 inch dead band is AUC8103, and the new damper I bought from Burlen last year with the 1/8 inch dead band is also AUC8103.

It looks to me like the damper was redesigned to make it simpler and more reliable. A new damper stateside is $33 USD but directly from Burlen it is only $13 USD. I'm going to buy another new damper from Burlen just to be sure they are equal.

I'm glad you mentioned springs........my springs have no color and they have tighter coil spacing on the ends in one carb, and equal spacing in the other carb. I may as well change those out too?

The 1/8 inch dead band makes sense now that I understand how they work. I didn't realize until we talked that those were acting as check valves.

[arcturus]

You may be well advised to purchase two dampers and have a matched pair for all the difference to the cost.

[Derek UK]

Springs are cheap and will add virtually nothing to postage from Burlen. If you are able too, it might be an idea to send Burlen a picture of the 2 dampers, indicating which one is the new one. Maybe get that clarified before you order. If Burlen have changed the design without altering the number you would expect them to have the same damping characteristics but I'd want them to look the same. From what you say, this pair don't match.
If you think you need any other small parts for the carbs it would be a good idea to include them in the order. As said, it shouldn't affect the postage unless it takes it to the next weight cost bracket.

[Ron Kwas]

volvogv;

It is crucial for springs to be the same!...their force is the most important component of the total counterforce that dashpot is lifted against!

Derek; "Load at length 4.5 oz @ 2.635 in. No sure how you measure that!" Since our carb springs are compression springs (opposed to tension springs), I think what they are talking about here is length spring would be compressed to, if 4.5oz were applied. Since Mike has noted that springs do look different, there's a good possibility that their Spring Constants may be different too.

I suggest he compare the two (by holding them straight...perhaps in a transparent tube) noting length, then applying the test mass, and again noting length. They obviously need to be quite similar!

I'm glad we are making good progress getting this resolved...it shows the elegance of the SU design...simple yes, but there is a lot going on there which has to work right...TIMES 2!!

Cheers from Connecticut!

[Ron Kwas]

Forum;

I have documented we have learned in the course of this investigation, particularly Function of the Damping Valve, and added this to my SU page: http://www.sw-em.com/su_carbs.htm#Da...lve%20Assembly

Cheers