Thread: Learn from my misjudgement
01-28-2010, 09:25 AM #1
Learn from my misjudgement
Wow...where to start here...
A few months back I had taken my stuff to a very very well known machine shop here in my hometown to do the bore/hone of both of my cylinders. This machine shop guy worked at GM for 30 years and has had his own personal shop for over 15 years and has built some of the most well known "late model" engines that runs in our local tracks. This guys reputation sheet has to be 30 pages long. So I though who better then this guy right? So I drop off my stuff to the guy and I leave him a piston for each set of cylinders to measure for proper clearance. Well I get a call from him a few days after I dropped them off and he said ok they are ready. I paid him double what he was going to charge me because he quoted me some stupid low price that was not even close to being a "good" deal for him, so I though if I pay him what I'm used to paying for this job...maybe I will get in good with the guy and if ever needed, get faster turn around time.
So I pick them up and noticed the hone job at best was poor ....but sent to Tim Judge for porting etc. Well Tim calls me up and says WOW who honed these things...they are rough...which I knew...but was planning on a final hone once ported either from TJ or the guy. I get them back about a month later and the machine shop guy said 1 week for honing so I took them to another very well known guy and a friend of mine to hone. Well when I asked the first guy about my "clearances" he stated they were 5.5 thou....even though I had asked for 4.5-5 but figured ehh..it will just be a little lose from what TJ told me to run. Well I drop them off and my new guy hones them and they look sweet. So I went ahead and put everything back together as you've all seen. I asked the new guy how much he thought he took off on the final hone process and he said .5 thou....so I was like ok...that puts me around 6 thou ....which was more then desired..but the engine would have still worked..
Well as I'm finishing up building these, I thought to myself a comment that he had made about measuring points when I dropped them off and if I recall ...he was talking about something near the pin...and it hit me like a brick about him not measuring from the bottom of the skirt up 10mm or about 3/8 of an inch and I was like this could be bad...real bad. So I get him on the phone and sure enough he measured at the pin and not where they are the largest...10mm up from skirt, which prompted a tear down.
So I take the twin back apart and measure the piston 3.206 and then took over the shop the cylinder and we measure the bored.... Top was 4.5 thou clear ...middle was 4 thou and the lower sleeve was only 2.5 thou....can you say BOMB???
So now due to my trusting this guy ...I could have blown up both engines and I really don't know what to think....geesh 2.5 thou clearance would have lasted 15-20 seconds before boom. So I am taking both apart and having my friend hone to desired clerances.
Long story like that short...
Never trust anyone...always check everyone's work....everyone!!! I went off this guys reputation that he was the "guy to go to" and the best around.
I was planning on taking them to FL for break in in March...that would have been a very very bad vacation with both skis's blown up. I can only assume this guy is not a "2" stroke PWC guy and he didn't know...although, measuring a bore and piston should be basic....it could have destoryed all that I have done!
01-28-2010, 09:45 AM #2
That sucks Mike, although it sounds like it could've been worse. Good judgement on your part to double check. Hope all the builds are coming along good.
01-28-2010, 10:50 AM #3
- Join Date
- Jun 2009
That is a hard lesson to learn right there glad you caught it. I was given some advise a long time ago about having machine work done at the wrong place. I was working at a automotive machine shop and my boss refused to bore a dirt bike cylinder, I asked him why. He said would you go to the dentist for a trasplant? I said no he goes why not he is a doctor I said yea but not in that field. He said exactly. He said I have been building sprint car motors for 20 years but I know nothing about machining a 2 stroke. I know people have had success with using automotive guys which is good for them.But why take the chance if you don`t really have to it could cost a lot more in the end.
01-28-2010, 11:15 AM #4
Sorry to hear this Mike
What was the temp when you measured it? Were the jugs the same temp..IE room temp? Pistons?
Did you happen to be in his actual shop?
01-28-2010, 11:24 AM #5
Make sure you tell the machinist that you measured his work and had to get it done over.If hes wants to do the right thing he should refund your money or at least some of it.
For less than $100 you can get a bore gauge and a Micrometer and check yourself.
My machinist knows I have the tools to check my own pistons and bores so he isnt going to try and give me out of spec work.
I didnt check mine after geting them done .As much as I dont want to because the rings are a real M.F,r I will be taking my cylinders back off to check clearance.I will let you know what they are like but because my machinist knows I check them I trully expect them to be good.
Im ordering a dome and some rings today im doing the head for the 99.When the parts come I will pull the cylinders do the head work and I will check clearance at that time.
01-28-2010, 11:28 AM #6
Oh when someone does good work they should have no problem with you checking it for quality because you can then turn around and tell everyone just how good they did.
01-28-2010, 11:39 AM #7
Before I would do anything, I would take them back to the guy who initially did the work, and ask him to take the measurements right in front of you.
Looks like he did wrong somehow.
Now I am not sticking up for him, but give those parts to 10 people who "can use" mics, dial indicators, bore gauges, etc, and I bet you get only a few who get the same measurement.
Hell, holding the part in your hand and warming it up will change what you get as far as size.
01-28-2010, 05:01 PM #8
That sucks! Glad to hear you found your problem I have a TJ ported stock bore 760. Lee
01-28-2010, 07:26 PM #9
wow MP.. good thing you checked.. I have learned thru the years to double check work (mine and theirs..)
this is how i caught the ring gap issue on the 500..
...quick old school test trick (Car Craft from the 70's)..slip an new unmounted ring into your newly bored and honed cylinder... as you move the ring into various spots down the cylinder, check the air gap... if it varies,investigate why!!
01-28-2010, 09:05 PM #10
Same temperatures...same parts....same bore dial indicator...
I borrowed some of my Wife's Father's big dollar Mic's and too my "reading" on the pistons well before I went over the the machine shop. I measured 3.206 which is the same exact measurement he did so we were completey dead even on our measurements.
As far as the bore measurements...the guy used to build engines for Yates racing "nascar" for like 11 years...and pretty sure he can use his 3k dial indicator. When measured...it was about 73F in his shop and he measured them 2 times...from top to bottom and found the same deal
Lastly..in terms of the guy who did the original bore/hone...it's a long story but I don't want to cause any issues with them because they both have done work for each other and I simply don't want to put him into the spot light... I'm just ready to have it fixed...
There is one good thing about this...ok maybe two..
1. I can deck my cylinders even more...
2. I get to "slide" it in a few more times into the holes =0)
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