"it Blowed Up, Sir"

Discussion in 'WERA Vintage' started by evilhordewannabe, Aug 11, 2002.

  1. Yamaha179

    Yamaha179 Well-Known Member

    Sounds like you had a great VIR! It's interesting the Richard Lucas' F RD spec bike is so fast. Maybe I ought to get Guido to put a contract out on him before the GNF...

    Roper is a trip too. I love watching him - can usually keep him in view for at least two turns. What is he, closing in on 50 years old and rides like the very wind. He's a neat guy.

    I wanted to ask Stan some questions about pistons too. You know he runs 2VO pistons (RD400F). One of the things he said was that the relief in the exhaust skirt on the other RD 400 pistons exposed the crankcase to the exhaust track and polluted the fresh intake charge (at least I think that is what he said). Bob Macaulay and I were talking about that last night and we aren't sure that's what is happening and I wanted to ask Stan about that. I do know that before I started running the RZ350 pistons I never had an intake skirt crack, but they are routine now. I'd like to go to the RD 400 pistons, but the 2V0 style are getting scarce.

    Will you be doing TGPR? North Florida? Roebling? Or do you have to show up for work some day? <BG>
    Lyn Garland
  2. RZ Racer

    RZ Racer It passed tech LAST time!

    I think he was refering to a motor that had problems in regards to the exhaust gasses heating the bottom end.
    I always have a great time at vir!! I's one of the best....
    I've managed to sneak out of work for one extra se round and that will be next week at tgpr. I have work conflicts w/ NFMP and endurance conflicts w/ RRR. I'll be at the final vir too.(You should come!!!)
    I'm trying not to tear the motor apart before the gnf, so I'll probably sit f500 out(117pts) and just run f-2stroke. You still been bringing the stocker to the track too? I know a diesel guy that would LOVE to try it out at RRR.
    The fastest thing about Richs bike used to be Rich. However, he has steadily made small improvements each year and never seems to take a step backwards. This year, it's the fastest I've seen it AND he still rides the snot out of it. He made mention of a "special" thanks to Stan & Tina when he was picking up his wood. I think new headwork was mentioned.....
  3. Yamaha Fan

    Yamaha Fan Well-Known Member


    Over the short 1+ years I have been back racing my experience with pistons is as follows:

    I have used 1 set of Wiseco PRO lights (RZ), several PRO-X RZ and rd400 (1A1)

    As Lyn said, 4-ish races (2 classes per race) is it for RZ’s (I ran them 2 years ago for most of the first season. Cracks appeared on the skirts angled from the reed holes outward to the skirt edge. I ran the Wiseco’s the first two races this year. They were set up on a new bore by Bill at BoreTech. I asked him to set the proper clearance based on his experience setting up Race RD’s in the past and did not measure them so I cannot tell you what clearance he provided. No sign of cracking but after Talladega (2 race dates, 4 races) I pulled the top end it measured just over .008 clearance. This was excessive to me, the bore measured .0016-.0017 over 65mm (4th over) I discussed this with a couple of people experienced with Wiseco pistons, the comment was that they do collapse quite a bit.

    I could not run RZ pistons as they are bore based sizing (nominally .002 under 65mm) but 1A1 pistons are sized at 65mm so I bead honed the cyls and dropped a set in

    I have run 1A1 pistons since with no crack issues. Checked the pistons after 3 races, (Putnam, Kershaw and Road A) practice days included at Putnam and Kershaw they looked fine. I did put new pistons in and kept the others as spares.

    I think the issue with the RZ pistons in the RD is that they are designed to be supported by the intake bridge, without it they are stressed to much by the intake port. I have a set of reeded TZ350G cylinders from the former sidecar world champ. The intake bottom is extremely V shaped, they used modified TZ350 pistons where they added the reed holes to the un-reinforced skirt (they could get away with that as the TZ750 turns the crank backward relieving the stress on the intake side) . We may not need to drop the floor of the port for performance reasons but ultimately may find that creating a very sharp V angle to the base of the intake port will eliminate the stress to the RZ piston skirt and eliminate or minimize the cracking.
    Last edited: Aug 18, 2002
  4. Yamaha179

    Yamaha179 Well-Known Member

    We (lBob M or I) have been taking the "spare" RD to all the races since he finished his bike and plan to take it to the rest of them also. If you know someone who wants a test ride on a two-stroke that might be worked out. We don't commit it for race day because one of us might do something dumb and need a back-up bike, but we'll lend it out for practice.
  5. Yamaha Fan

    Yamaha Fan Well-Known Member

    Will you be at pracitice on Friday???
  6. boiade

    boiade Well-Known Member

    Rings and pistons on my TD-3 have two seasons on them and I can feel that the bike is not as "peppy" as two years ago. I have NOS TD-3 pistons for 3 upsizes, the difference is .1 mm (very small) beween piston sizes as the chrome bores don't wear very much. Does anyone have an idea of the optimum clearance between the piston and the bore for chromed cylinders? I'd hate to put new pistons in and seize because the bores hadn't worn enough!

    The DS-7 was a hoot first races out at VIR. I ran it in 350 GP and Mark ran it in 500 GP. We had a powow about jetting after practice (what a practice for Mark, he only hooked up one fuel line and had to push it back from turn one to get 1 or 2 laps in on it), and we decided to lean it one jet size and it was the right decision. If it wasn't for Roper on the MANX, Mark would have won 500 GP on a little 250cc air-cooled 2-stroke. It was the first race for the bike and I was happy to take 4th in the 350 GP class as there were a few 350GP regulars behind me. We had to contend with a clutch that wasn't a clutch it dragged when sitting still and slipped when power came on at the same time, the starts were nerve wracking, you had to keep it at above 7K RPM to keep the bike for dying at the start. I replaced the clutch this evening with all new friction plates and springs and when I dismantled it I noticed I had mixed 2 dry-clutch and 4 wet-clutch friction plates, I had also put one (thicker) dry clutch metal plate in the basket! I put in new Barnett wet-clutch plates and miked the metal plates and now the clutch works, duh. Mark finally had a chance to race a piston port 2-stroke and I think he enjoyed the narrow power band, it is a challenge. I put the clutch together this winter and may have had a few glasses of Brunello di Montalcino, so I can be forgiven.

    It really is interesting to compare notes with someone racing the same bike. A new experience for me.
  7. Yamaha179

    Yamaha179 Well-Known Member

    Proper piston-to-cylinder clearance for an air cooled Yamaha twin is .040 to .045mmor .0016 to .0018 inch. You should measure this clearance with a dial bore gauge and a micrometer - do not, I say again, do not try to use a feeler gauge. It isn't accurate enough. If your local shop can't measure your bits for you send them to me and I'll measure them free of charge.
    Lyn Garland
  8. RZ Racer

    RZ Racer It passed tech LAST time!

    Fred- That little puppy was a blast! I knew it couldn't be the oil that you were using that caused so much slippage. I never did get past 9.5krpms in 6th gear. Do you think we should go down a tooth or is that as fast as the gerbils can run?:D Assuming my ride isn't dragging me out of there next month, I'll make sure to have a good bottle of grapes for afterwards. Thanks again!!
  9. boaide

    boaide Well-Known Member


    I know the clearances for standard steel liner cylinders, but wonder if they are the same for alloy cylinders with chrome bores, i.e. given that you are stuck with set piston oversizes in .01mm (from.96 std, to .99) increments and no ability to adjust the bore, you'd think that from standard, you would replace the piston when you wore .01mm of the chrome from standard.


    I think that we may want 2 more teeth on the rear. I wasn't getting into 6th until after the kink on the front straight, maybe with 2 more teeth we can be at top speed at the kink. First will be quite low with the stock wide-ratio box but there is no 1st gear corner at VIR anyway. Just have to keep the front wheel down at the start.

  10. YAM#849

    YAM#849 y'all watch this...

    Re: pistons

    Do you have Harry's phone #? from the US it's,
    011 44 116 287 1285. (also, they're five hours ahead of our eastern time). He's got the Wiseco RZ pistons working well in his 400 engines. And high rpm doesn't seem to hurt them. All I know is that he's not making the intakes as big as he used to years ago, and it's not hurting horsepower. I bet he can help figure out what you'd need to change to get them to last.
  11. Yamaha179

    Yamaha179 Well-Known Member

    Those piston clearance numbers are good for chrome, nikasil, or iron AIR COOLED only. Water pumpers want more clearance and are subject to cold seizures.
  12. boaide

    boaide Well-Known Member


    Thanks, I guess that you have to hope that you've worn at least .01mm of chrome when you want to install the next piston size.

  13. Yamaha Fan

    Yamaha Fan Well-Known Member

    Re: Re: pistons

    Thanks for Harry's # Carl, I did not have cracking problems with the wiseco's and believe that because they are forged that I would not have any either. My issue with them was the large clearance that showed up after 2 runs (2 full practice days and 4 races total). I am a fan of cast pistons, maybe I should not worry about the clearance. When I pulled the Wiseco top end to inspect it the pistons looked fine but there was some forging/wiping of the aluminum around both lower rings and they were stuck. The rings did not appear damaged but they were defiantly stuck for about 50% of the bore.

    I ran some high compression heads (a one piece Daytona head) for the first practice session on the motor but pulled it after continuous Head gasket leek problems. A little later Lyn was kind enough to CC the head and motor with me and I found that the static compression ratio was way to high. I wonder if that caused the damage (heat build up). Since this issue I have run a set of standard RD400 heads with no problem. I intend to add a few CC’s to the Daytona heads and I have cut it in two.

  14. YAM#849

    YAM#849 y'all watch this...

    When I was running my 400 with Wiseco's, I would check the rings after the first race weekend. Usually, there was some light sticking around the exhaust side. I'd remove the rings and lightly debur the edges of the lands with a little file, and they were fine after that. ( I'm ready for the howls from the 4 strokers about working on pistons after only one race- but that's the price of BMEP)

    PS I usually only get 4 weekends on a piston ring with my 175, but the Wiseco lasts thru several rings. Of course, it doesn't have windows, either...
  15. Diesel

    Diesel Well-Known Member

    You won't hear anything but only mild ribbing from me. Last year I tore down my Honda 175 after every race. It was the only way to see whether or not new performance "enhancements" were a reliability risk.

    STAN LIPERT Well-Known Member

    Rich Lucas is officially sponsored by Tina Lipert and Stan Lipert,I supply free work for Rich,if he can use it.Crank building, head work,and technical advice for now.He is completely responsible for how his bike runs,his own tuning and part selection,and yes,he has a measured conservative methodology.I raced against Roper,the Manx has,in my opinion,about 50HP,maybe 52 tops.
    I think the exhaust-in-crankcase is messing with the jetting and heating the intake,I have to share my symptoms with you when I have time.Call me at work?
    Weiscos shrink,the looser clearance,the faster,for that matter,all forged pistons shrink,two stroke and four.They simply don't have enough silicon,limited by the nature of their construction.There is enough of a difference between the TZ motor with the V-port and RD motor,I'd suggest you try something else.
    I don't think you will ever see a forged piston crack,they are simply too soft,which is why they are more likely to melt and seize,I know they have to be changed out so often,so I consentrated my trials with finding a cast piston to work.Lynn believes that Hurst and Spargo have to change out their Weiscos after 3 races,maybe you can confirm this?Shink or crack,you choose your piston.
    Tidbit:embedded in this BBS are posted every spec to my bike except for how much compression!
  17. boiade

    boiade Well-Known Member

    Factory specs for a late model 500cc Manx were 50HP at 7,200 RPM. In the late 60s early 70s when the privateers ran them with 4-speed AMC boxes they would be tuned/modified to put out 55-60 HP 8,000 rpm and come off the line with difficulty with the 4-speed box. Roper has an Austrian made 6-speed close-ratio box with a super low first gear, so I figure he can run more peaky so maybe he has more than 60 HP. Roper is good, but he passed Rich and Gene on the first lap at the kink on front straight at VIR and he was doing 10-20 MPH more than the RDs.
  18. 50Joe

    50Joe Registered User

    This thread is way cool.
  19. WERA33

    WERA33 Well-Known Member

    rd's must be hard on pistons. ill check my race book in the morning, but i have
    five race weekends so far this year on my rz. i enter form 2stroke and v5 and an occasional practice day. these are the same pistons i ran last year. rz's may be easy on wear. oh, and these are wiseco's.
  20. YAM#849

    YAM#849 y'all watch this...

    Those guys often run 4 races per weekend on the 400's. ( in AHRMA, F500 twice, Formula Vintage twice, plus practices ) After three of those weekends, it's entirely possible the bike would be due for pistons. It should be measured, for sure. Perhaps Chris will get on here and give a more exact answer as to what he does.
    This is one of those deals where you must compare apples to apples. A 400 making 70 hp is going to go thru more pistons than one making 50hp. Then again, it doesn't eat pistons anywhere near as fast as a TZ350-G making 80 hp.

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